# Programming with gtkmm 4

Murray Cumming
Bernhard Rieder Chapter on "Timeouts".
Jonathon Jongsma Chapter on "Drawing with Cairo". Chapter on "Working with gtkmm's Source Code". Chapter on "Recent Files".
Ole Laursen Parts of chapter on "Internationalization".
Marko Anastasov Chapter on "Printing". Parts of chapter on "Internationalization".
Daniel Elstner Section "Build Structure" of chapter on "Wrapping C Libraries with gmmproc".
Chris Vine Chapter on "Multi-threaded programs".
David King Section on Gtk::Grid.
Pedro Ferreira Chapter on "Keyboard Events".
Kjell Ahlstedt Update from gtkmm 3 to gtkmm 4. Chapter on "Building applications". Chapter on "The DropDown Widget". Chapter on "ListView, GridView, ColumnView".
Daniel Boles Notes on need to remove widgets in non-managed wrappers from parents to dispose, other tweaks.

This book explains key concepts of the gtkmm C++ API for creating user interfaces. It also introduces the main user interface elements ("widgets").

2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Murray Cumming

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

## Introdução

### Este livro

This book explains key concepts of the gtkmm C++ API for creating user interfaces. It also introduces the main user interface elements ("widgets"). Although it mentions classes, constructors, and methods, it does not go into great detail. Therefore, for full API information you should follow the links into the reference documentation.

This book assumes a good understanding of C++, and how to create C++ programs.

Gostaríamos muito de ouvir sobre quaisquer problemas que tenha em aprender sobre gtkmm com este documento, e agradeceríamos informações sobre melhorias. Por favor, veja a seção Contribuindo para maiores informações.

### gtkmm

gtkmm is a C++ wrapper for GTK, a library used to create graphical user interfaces. It is licensed using the LGPL license, so you can develop open software, free software, or even commercial non-free software using gtkmm without purchasing licenses.

gtkmm was originally named gtk-- because GTK was originally named GTK+ and had a + in the name. However, as -- is not easily indexed by search engines, the package generally went by the name gtkmm, and that's what we stuck with.

#### Why use gtkmm instead of GTK?

gtkmm allows you to write code using normal C++ techniques such as encapsulation, derivation, and polymorphism. As a C++ programmer you probably already realize that this leads to clearer and better organized code.

O gtkmm tem melhor segurança quanto à tipagem, assim o compilador pode detectar erros que só seriam percebidos em tempo de execução ao usar C. Esse uso de tipos específicos também torna a API mais clara, porque você pode ver que tipos deveriam ser usados apenas olhando a declaração de um método.

Inheritance can be used to derive new widgets. The derivation of new widgets in GTK C code is so complicated and error prone that almost no C coders do it. As a C++ developer you know that derivation is an essential Object Orientated technique.

Member instances can be used, simplifying memory management. All GTK C widgets are dealt with by use of pointers. As a C++ coder you know that pointers should be avoided where possible.

gtkmm involves less code compared to GTK, which uses prefixed function names and lots of cast macros.

#### gtkmm comparado ao Qt

O Qt da Trolltech é o competidor mais próximo do gtkmm, então merece uma discussão.

gtkmm developers tend to prefer gtkmm to Qt because gtkmm does things in a more C++ way. Qt originates from a time when C++ and the standard library were not standardized or well supported by compilers. It therefore duplicates a lot of stuff that is now in the standard library, such as containers and type information. Most significantly, Trolltech modified the C++ language to provide signals, so that Qt classes cannot be used easily with non-Qt classes. gtkmm was able to use standard C++ to provide signals without changing the C++ language. See the FAQ for more detailed differences.

#### gtkmm é um wrapper

gtkmm is not a native C++ toolkit, but a C++ wrapper of a C toolkit. This separation of interface and implementation has advantages. The gtkmm developers spend most of their time talking about how gtkmm can present the clearest API, without awkward compromises due to obscure technical details. We contribute a little to the underlying GTK code base, but so do the C coders, and the Perl coders and the Python coders, etc. Therefore GTK benefits from a broader user base than language-specific toolkits - there are more implementers, more developers, more testers, and more users.

### C++ Resources

Useful links:

- Wikipedia C++: An introduction to C++, and many links.

- C++ reference: A convenient version of the C and C++ standards.

- The C++ Resources Network

- Bjarne Stroustrup's homepage

## Instalação

### Dependências

Before attempting to install gtkmm-4.0, you might first need to install these other packages.

- sigc++-3.0

- gtk4

- glibmm-2.68

- cairomm-1.16

- pangomm-2.48

Essas dependências têm suas próprias dependências, incluindo os seguintes aplicativos e bibliotecas:

- pkg-config

- glib-2.0

- pango

- cairo

- gdk-pixbuf-2.0

- graphene-1.0

### Unix e Linux

#### Pacotes pré-compilados

Versões recentes do gtkmm hoje são empacotadas por quase todas as grandes distribuições Linux. Assim, se você usa Linux, é bem possível que possa começar com o gtkmm instalando o pacote do repositório oficial da sua distribuição. Algumas que incluem gtkmm em seus repositórios são Debian, Ubuntu, Red Hat, Fedora, Mandriva, Suse e muitas outras.

The names of the gtkmm packages vary from distribution to distribution (e.g. libgtkmm-4.0-dev on Debian and Ubuntu or gtkmm4.0-devel on Red Hat and Fedora), so check with your distribution's package management program for the correct package name and install it like you would any other package.

The package names will not change when new API/ABI-compatible versions of gtkmm are released. Otherwise they would not be API/ABI-compatible. So don't be surprised, for instance, to find gtkmm 4.8 supplied by Debian's libgtkmm-4.0-dev package.

#### Instalando pelo código fonte

If your distribution does not provide a pre-built gtkmm package, or if you want to install a different version than the one provided by your distribution, you can also install gtkmm from source. The source code for gtkmm can be downloaded from .

After you've installed all of the dependencies, download the gtkmm source code, unpack it, and change to the newly created directory. gtkmm can be built with Meson. See the `README` file in the gtkmm version you've downloaded.

Remember that on a Unix or Linux operating system, you will probably need to be `root` to install software. The `su` or `sudo` command will allow you to enter the `root` password and have `root` status temporarily.

The `configure` script or `meson` will check to make sure all of the required dependencies are already installed. If you are missing any dependencies, it will exit and display an error.

By default, gtkmm if built with Meson or Autotools, will be installed under the `/usr/local` directory. On some systems you may need to install to a different location. For instance, on Red Hat Linux systems you might use the `--prefix` option with configure, like one of:

    # meson setup --prefix=/usr <builddir> <srcdir>
    # meson configure --prefix=/usr
    # ./configure --prefix=/usr

Tenha muito cuidado ao instalar em prefixo padrões do sistema como `/usr`. As distribuições Linux instalam pacotes de programas em `/usr`, então instalar um pacote fonte neste prefixo poderia corromper ou conflitar com os programas instalados usando o sistema de gerenciamento de pacotes da sua distribuição. Idealmente, você deveria usar um prefixo separado para todos os softwares que você instalar a partir do código-fonte.

Se você quiser ajudar a desenvolver o gtkmm ou experimentar novos recursos, você pode instalar o gtkmm a partir do git. A maioria dos usuários nunca precisarão fazer isso, mas se estiver interessado em ajudar no desenvolvimento do gtkmm , veja o apêndice Trabalhando com o código-fonte do gtkmm.

### Microsoft Windows

GTK and gtkmm were designed to work well with Microsoft Windows, and the developers encourage its use on the win32 platform. However, Windows has no standard installation system for development libraries. Please see the Windows Installation page (somewhat outdated) or the gtkmm and Win32 appendix for Windows-specific installation instructions and notes.

## Básico

Este capítulo irá introduzir alguns dos aspectos mais importantes de um código com gtkmm. Isso será demonstrado com um código de exemplo simples e funcional. Mas isso é só um aperitivo, então você precisará olhar os outros capítulos para informações mais substanciais.

Your existing knowledge of C++ will help you with gtkmm as it would with any library. Unless we state otherwise, you can expect gtkmm classes to behave like any other C++ class, and you can expect to use your existing C++ techniques with gtkmm classes.

### Exemplo simples

Para iniciar a introdução ao gtkmm, comecemos com o programa mais simples possível. Este programa cria uma janela vazia com 200 x 200 pixels.

Source Code

File: `base.cc` (For use with gtkmm 4)

    #include <gtkmm.h>

    class MyWindow : public Gtk::Window
    {
    public:
      MyWindow();
    };

    MyWindow::MyWindow()
    {
      set_title("Basic application");
      set_default_size(200, 200);
    }

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.examples.base");

      return app->make_window_and_run<MyWindow>(argc, argv);
    }

We will now explain each part of the example

    #include <gtkmm.h>

All gtkmm programs must include certain gtkmm headers; `gtkmm.h` includes the entire gtkmm kit. This is usually not a good idea, because it includes a megabyte or so of headers, but for simple programs, it suffices.

The next part of the program:

    class MyWindow : public Gtk::Window
    {
    public:
      MyWindow();
    };

    MyWindow::MyWindow()
    {
      set_title("Basic application");
      set_default_size(200, 200);
    }

defines the MyWindow class. Its default constructor sets the window's title and default (initial) size.

The `main()` function's first statement:

    auto app = Gtk::Application::create("org.gtkmm.examples.base");

creates a Gtk::Application object, stored in a Glib::RefPtr smartpointer. This is needed in all gtkmm applications. The create() method for this object initializes gtkmm.

The last line creates and shows a window and enters the gtkmm main processing loop, which will finish when the window is closed. Your `main()` function will then return with an appropriate success or error code. The argc and argv arguments, passed to your application on the command line, can be checked when make_window_and_run() is called, but this simple application does not use those arguments.

    return app->make_window_and_run<MyWindow>(argc, argv);

After putting the source code in `base.cc` you can compile the above program with gcc using:

    g++ base.cc -o base `pkg-config --cflags --libs gtkmm-4.0` -std=c++17

Note that you must surround the pkg-config invocation with backquotes. Backquotes cause the shell to execute the command inside them, and to use the command's output as part of the command line. Note also that `base.cc` must come before the pkg-config invocation on the command line. `-std=c++17` is necessary only if your compiler is not C++17 compliant by default.

### Cabeçalhos e vinculação

Although we have shown the compilation command for the simple example, you really should use the Meson build system. The examples used in this book are included in the gtkmm-documentation package, with appropriate build files, so we won't show the build commands in future. The `README` file in gtkmm-documentation describes how to build the examples.

Para simplificar a compilação, usaremos o `pkg-config`, que está presente em todas as instalações do gtkmm (se instaladas apropriadamente). Esse programa "sabe" quais opções de compilador são necessárias para compilar os programa que usam gtkmm. A opção `--cflags` faz com que o `pkg-config` emita uma lista de diretórios de inclusão para o compilador buscar; a opção `--libs` solicita a lista de bibliotecas às quais o compilador deve vincular e os diretórios onde achá-los. Experimente executá-lo no seu prompt do shell para ver os resultados no seu sistema.

However, this is even simpler when using the `dependency()` function in a `meson.build` file with Meson. For instance:

    gtkmm_dep = dependency('gtkmm-4.0', version: '>= 4.6.0')

This checks for the presence of gtkmm and defines `gtkmm_dep` for use in your `meson.build` files. For instance:

    exe_file = executable('my_program', 'my_source1.cc', 'my_source2.cc',
      dependencies: gtkmm_dep,
      win_subsystem: 'windows',
    )

gtkmm-4.0 is the name of the current stable API. There are older APIs called gtkmm-2.4 and gtkmm-3.0 which install in parallel when they are available. There are several versions of gtkmm-2.4, such as gtkmm 2.10 and there are several versions of the gtkmm-3.0 API. Note that the API name does not change for every version because that would be an incompatible API and ABI break. There might be a future gtkmm-5.0 API which would install in parallel with gtkmm-4.0 without affecting existing applications.

If you start by experimenting with a small application that you plan to use just for yourself, it's easier to start with a `meson.build` similar to the `meson.build` files in the Building applications chapter.

If you use the older Autotools build system, see also the GNU site. It has more information about autoconf and automake. There are also some books describing Autotools: "GNU Autoconf, Automake, and Libtool" by Gary Vaughan et al. and "Autotools, A Practitioner's Guide to GNU Autoconf, Automake, and Libtool" by John Calcote.

### Widgets

gtkmm applications consist of windows containing widgets, such as buttons and text boxes. In some other systems, widgets are called "controls". For each widget in your application's windows, there is a C++ object in your application's code. So you just need to call a method of the widget's class to affect the visible widget.

Widgets are arranged inside container widgets such as frames and notebooks, in a hierarchy of widgets within widgets. Some of these container widgets, such as Gtk::Grid, are not visible - they exist only to arrange other widgets. Here is some example code that adds 2 Gtk::Button widgets to a Gtk::Box container widget:

    m_box.append(m_Button1);
    m_box.append(m_Button2);

and here is how to add the Gtk::Box, containing those buttons, to a Gtk::Frame, which has a visible frame and title:

    m_frame.set_child(m_box);

A maioria dos capítulos deste livro trata de widgets específicos. Veja a seção Widgets contêineres para mais detalhes sobre a adição de widgets a widgets contêineres.

Although you can specify the layout and appearance of windows and widgets with C++ code, you will probably find it more convenient to design your user interfaces with `.ui` XML files and load them at runtime with Gtk::Builder. See the Gtk::Builder chapter.

Although gtkmm widget instances have lifetimes and scopes just like those of other C++ classes, gtkmm has an optional time-saving feature that you will see in some of the examples. The `Gtk::make_managed()` allows you to create a new widget and state that it will become owned by the container into which you place it. This allows you to create the widget, add it to the container and not be concerned about deleting it, since that will occur when the parent container (which may itself be managed) is deleted. You can learn more about gtkmm memory management techniques in the Memory Management chapter.

### Sinais

O gtkmm, como a maioria dos kits de ferramentas para GUI, é orientado a eventos. Quando um evento ocorre, como o pressionar de botão do mouse, o sinal apropriado será emitido pelo widget que foi pressionado. Cada widget tem um conjunto de sinais diferente que pode emitir. Para fazer um clique de botão resultar em uma ação, nós configuramos um manipulador de sinais para capturar o sinal "clicked" do botão.

gtkmm uses the libsigc++ library to implement signals. Here is an example line of code that connects a Gtk::Button's "clicked" signal with a signal handler called "on_button_clicked":

    m_button1.signal_clicked().connect( sigc::mem_fun(*this,
      &HelloWorld::on_button_clicked) );

Para informações mais detalhadas sobre sinais, veja o apêndice.

Para informações sobre como implementar seus próprios sinais em vez de apenas conectar os sinais gtkmm existentes, veja o apêndice.

### Glib::ustring

You might be surprised to learn that gtkmm doesn't use std::string in its interfaces. Instead it uses Glib::ustring, which is so similar and unobtrusive that you could actually pretend that each Glib::ustring is a std::string and ignore the rest of this section. But read on if you want to use languages other than English in your application.

std::string uses 8 bits per character, but 8 bits aren't enough to encode languages such as Arabic, Chinese, and Japanese. Although the encodings for these languages have been specified by the Unicode Consortium, the C and C++ languages do not yet provide any standardized Unicode support for UTF-8 encoding. GTK and GNOME chose to implement Unicode using UTF-8, and that's what is wrapped by Glib::ustring. It provides almost exactly the same interface as std::string, along with automatic conversions to and from std::string.

Um dos benefícios do UTF-8 é que você não precisa usá-lo a menos que queira, então não precisa mexer no seu código todo de uma vez. std::string funcionará também com textos ASCII 7 bits. Porém, quando você tentar fazer a localização do seu aplicativo para idiomas como chinês, por exemplo, você comerçará a ver uns erros estranhos, e possivelmente uns travamentos. Então, tudo que você precisa fazer é começar a usar Glib::ustring no lugar.

Note que UTF-8 não é compatível com codificações de 8 bits como ISO-8859-1. Por exemplo, os tremas alemães (umlaut) não estão na faixa ASCII e precisam de mais que 1 byte na codificação UTF-8. Se seu código contém textos constantes em 8 bits, você tem que convertê-los para UTF-8 (exemplo: o cumprimento da Bavária "Grüß Gott" seria "Gr\xC3\xBC\xC3\x9F Gott").

Você deveria evitar aritmética de ponteiros no estilo C e funções como strlen(). Em UTF-8, cada caractere pode precisar em algum lugar de 1 a 6 bytes, então não é possível assumir que o próximo byte é outro caractere. Glib::ustring se preocupa com esses detalhes para você para que possa usar métodos tais como Glib::ustring::substr() enquanto ainda raciocina em termos de caracteres em vez de bytes.

Ao contrário da solução Unicode UCS-2 do Windows, ele não exige quaisquer opções especiais do compilador para processar textos contantes, além de não gerar executáveis e biblioteca Unicode que sejam incompatíveis com os em ASCII.

Reference

Veja a seção Internacionalização para informações sobre como fornecer textos constantes em UTF-8.

### Misturando APIs C e C++

You can use C APIs which do not yet have convenient C++ interfaces. It is generally not a problem to use C APIs from C++, and gtkmm helps by providing access to the underlying C object, and providing an easy way to create a C++ wrapper object from a C object, provided that the C API is also based on the GObject system.

To use a gtkmm instance with a C function that requires a C GObject instance, use the C++ instance’s `gobj()` function to obtain a pointer to the underlying C instance. For example:

    Gtk::Button button("example");
    gtk_button_do_something_that_gtkmm_cannot(button.gobj());

To obtain a gtkmm instance from a C GObject instance, use one of the many overloaded `Glib::wrap()` functions. The C instance’s reference count is not incremented, unless you set the optional take_copy argument to `true`. For example:

    GtkButton* cbutton = get_a_button();
    Gtk::Button* button = Glib::wrap(cbutton);
    button->set_label("Now I speak C++ too!");

The C++ wrapper shall be explicitly deleted if

- it's a widget or other class that inherits from Gtk::Object, and

- the C instance has a floating reference when the wrapper is created, and

- `Gtk::manage()` has not been called on it (which includes if it was created with `Gtk::make_managed()`), or

- `Gtk::manage()` was called on it, but it was never added to a parent.

`Glib::wrap()` binds the C and C++ instances to each other. Don't delete the C++ instance before you want the C instance to die.

In all other cases the C++ instance is automatically deleted when the last reference to the C instance is dropped. This includes all `Glib::wrap()` overloads that return a Glib::RefPtr.

### Olá mundo em gtkmm

Agora já aprendemos o suficiente para dar uma olhada em um exemplo real. Conforme uma antiga tradição da ciência da computação, apresentaremos um Olá, mundo, à la gtkmm:

Source Code

File: `helloworld.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_HELLOWORLD_H
    #define GTKMM_EXAMPLE_HELLOWORLD_H

    #include <gtkmm/button.h>
    #include <gtkmm/window.h>

    class HelloWorld : public Gtk::Window
    {

    public:
      HelloWorld();
      ~HelloWorld() override;

    protected:
      //Signal handlers:
      void on_button_clicked();

      //Member widgets:
      Gtk::Button m_button;
    };

    #endif // GTKMM_EXAMPLE_HELLOWORLD_H

File: `helloworld.cc` (For use with gtkmm 4)

    #include "helloworld.h"
    #include <iostream>

    HelloWorld::HelloWorld()
    : m_button("Hello World")   // creates a new button with label "Hello World".
    {
      // Sets the margin around the button.
      m_button.set_margin(10);

      // When the button receives the "clicked" signal, it will call the
      // on_button_clicked() method defined below.
      m_button.signal_clicked().connect(sigc::mem_fun(*this,
                  &HelloWorld::on_button_clicked));

      // This packs the button into the Window (a container).
      set_child(m_button);
    }

    HelloWorld::~HelloWorld()
    {
    }

    void HelloWorld::on_button_clicked()
    {
      std::cout << "Hello World" << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "helloworld.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<HelloWorld>(argc, argv);
    }

Tente compilá-lo e executá-lo antes de continuar. Você deveria ver algo assim:

Olá, Mundo

Bem empolgante, hein? Vamos examinar o código. Primeiro, a classe HelloWorld:

    class HelloWorld : public Gtk::Window
    {
    public:
      HelloWorld();
      ~HelloWorld() override;

    protected:
      //Signal handlers:
      void on_button_clicked();

      //Member widgets:
      Gtk::Button m_button;
    };

This class implements the "Hello World" window. It's derived from Gtk::Window, and has a single Gtk::Button as a member. We've chosen to use the constructor to do all of the initialization work for the window, including setting up the signals. Here it is, with the comments omitted:

    HelloWorld::HelloWorld()
    : m_button("Hello World")
    {
      m_button.set_margin(10);
      m_button.signal_clicked().connect(sigc::mem_fun(*this,
        &HelloWorld::on_button_clicked));
      set_child(m_button);
    }

Notice that we've used an initializer statement to give the `m_button` object the label "Hello World".

Next we call the Button's set_margin() method. This sets the amount of space around the button.

Depois, associamos um manipulador para o sinal `clicked` de `m_button`. Ele emitirá nosso cumprimento amistoso para `stdout`.

Next, we use the Window's set_child() method to put `m_button` in the Window. The set_child() method places the Widget in the Window.

Agora vamos olhar para a função `main()` do nosso programa. Aqui está, sem os comentários:

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");
      return app->make_window_and_run<HelloWorld>(argc, argv);
    }

First we instantiate an object stored in a Glib::RefPtr smartpointer called `app`. This is of type Gtk::Application. Every gtkmm program must have one of these.

Next we call make_window_and_run() which creates an object of our HelloWorld class, shows that Window and starts the gtkmm event loop. During the event loop gtkmm idles, waiting for actions from the user, and responding appropriately. When the user closes the Window, make_window_and_run() will return, causing our `main()` function to return. The application will then finish.

Like the simple example we showed earlier, this Hello World program does not use the command-line parameters.

## Mudanças na gtkmm 3

gtkmm-3.0 is an old version of the gtkmm API that installs in parallel with the still older gtkmm-2.4 API and the new gtkmm-4.0 API. The last version of the gtkmm-2.4 API was gtkmm 2.24. gtkmm 3 has no major fundamental differences to gtkmm 2 but does make several small changes that were not possible while maintaining binary compatibility. If you never used the gtkmm-2.4 API then you can safely ignore this chapter.

A biblioteca gtkmm 3 é chamada `libgtkmm-3.0` em vez de `libgtkmm-2.4` e instala seus cabeçalhos em um diretório com a mesma versão, assim sua verificação pkg-config, deve pedir por `gtkmm-3.0` em vez de `gtkmm-2.4`.

gtkmm 3 adicionou algumas novas classes:

1. Gtk::AppChooser, Gtk::AppChooserButton, Gtk::AppChooserDialog permite ao usuário selecionar uma aplicação instalada para abrir um determinado tipo de conteúdo.

2. Gtk::Grid is a new container widget that will eventually replace Gtk::Box and Gtk::Table. It arranges its children according to properties of those children rather than its own layout details.

3. Gtk::Switch displays On/Off states more explicitly than Gtk::CheckButton. It may be useful, for instance, when allowing users to activate hardware.

gtkmm 3 também fez várias pequenas mudanças na API, que provavelmente você encontrará quando portar o código usado na gtkmm-2.4. Aqui está uma pequena lista:

1. Gtk::CellLayout, utilizado pela Gtk::IconView, Gtk::TreeView::Column e Gtk::ComboBox, agora tem uma Gtk::CellArea que pode ser usado para especificar mais detalhes sobre como a CellRenderer são dispostos e alinhados.

2. Gtk::ComboBox agora deriva de CellLayout, permitindo uma fácil distribuição e alinhamento das suas Gtk::CellRenderer.

3. Gtk::Adjustment, IconSet e Gdk::Cursor agora são usados através de Glib::RefPtr.

4. Gtk::Box, Gtk::ButtonBox, Gtk::IconView, Gtk::Paned, Gtk::ProgressBar, Gtk::ScaleButton, Gtk::Scrollbar e Gtk::Separator agora derivam de Gtk::Orientable, permitindo que sua orientação (vertical ou horizontal) seja especificado sem exigir o uso de uma classe derivada, tal como Gtk::HBox.

5. Gtk::IconView, Gtk::TextView, Gtk::TreeView e outros widgets derivam de Scrollable em vez de ter seus próprios métodos, como get_vadjustment() e ao invés de ter seu próprio sinal set_scroll_adjustments.

6. Gtk::Style e Gtk::Rc foram removidos, substituídos por Gtk::StyleContext, e Gtk::StyleProvider, tal como Gtk::CssProvider.

7. Widget::on_expose_event() foi substituido por Widget::on_draw(), que assume que cairomm é utilizado para desenho, por meio do Cairo::Context e não requer que você chame Cairo::Context::clip().

8. Gdk::RGBA substitui Color, adicionando um componente alfa para a opacidade. Colormap foi removido, juntamente com o seu uso difícil de alocar cores.

9. Gdk::Pixmap and Gdk::Bitmap were removed in favor of Gdk::Pixbuf.

10. Gdk::Drawable foi removido, com seus método movidos para Gdk::Window.

11. Agora usamos std::vector em vários métodos, em vez do tipo intermediário *Handle para fazer a API mais clara.

All deprecated API was removed in gtkmm 3.0, though there have been new deprecations in later gtkmm 3.x versions.

As a first step to porting your source code to gtkmm-3.0 you should probably ensure that your application builds with the deprecated gtkmm-2.4 API disabled, by defining macro such as GTKMM_DISABLE_DEPRECATED. There are some autotools macros that can help with this by defining them optionally at build time. See the gtkmm 3 porting wiki page for more details.

## Changes in gtkmm-4.0 and glibmm-2.68

gtkmm-4.0 is a new version of the gtkmm API that installs in parallel with the older gtkmm-2.4 and gtkmm-3.0 APIs. The last version of the gtkmm-3.0 API is gtkmm 3.24. gtkmm 4 has no major fundamental differences to gtkmm 3 but does make several changes (both small and large ones) that were not possible while maintaining binary compatibility. If you never used the gtkmm-3.0 API then you can safely ignore this chapter.

gtkmm 4's library is called `libgtkmm-4.0` rather than `libgtkmm-3.0` and installs its headers in a similarly-versioned directory, so your pkg-config check should ask for `gtkmm-4.0` rather than `gtkmm-3.0`.

gtkmm-4.0 is used in combination with glibmm-2.68, which sets the global locale for your program. The older glibmm-2.4 does not do that, and gtkmm-3.0 does it only to some extent. What this means is briefly that if your gtkmm-3.0 program contains a call to `std::locale::global(std::locale(""))`, you can probably remove it. If you don't want glibmm or gtkmm to set the global locale for you, you should add a call to `Glib::set_init_to_users_preferred_locale(false)` before any call to `Glib::init()` or Gtk::Application::create(). See the glibmm reference.

There are lots and lots of differences between gtkmm-3.0 and gtkmm-4.0. The following lists are not complete.

There are some important behavioural changes, to which you must adapt when migrating:

- Whereas in gtkmm-3.0, destruction of a non-managed C++ widget wrapper caused the wrapped GtkWidget to be destroyed, changes in GTK4 mean that in gtkmm-4.0 this canʼt always be the case. GTK4 has no uniform way to remove a widget from a parent, as GTK3 did with Gtk::Container::remove(), so gtkmm-4.0 canʼt do the removal for you as gtkmm-3.0 did. Hence, if a non-managed C++ widget instance is destructed while the widget is a child of another, gtkmm-4.0 wonʼt remove it from the parent, the parent retains a ref that stops the child being disposed, and the GtkWidget stays alive. The end result is that to destroy a non-managed widget with its C++ wrapper you must first remove it from its parent (however that parent allows) so the C++ wrapperʼs dtor can drop the final reference.

Some new classes were added in gtkmm 4 and glibmm 2.68:

1. Glib::ExtraClassInit and Gtk::Snapshot: These classes are needed only for writing custom widgets. See the Custom Widgets section.

2. Gtk::EventControllerKey, Gtk::EventControllerMotion, Gtk::EventControllerScroll and Gtk::GestureStylus

3. Gdk::Paintable, Gdk::Texture, Gtk::Picture and Gtk::WidgetPaintable

4. Gdk::Window has been renamed to Gdk::Surface. (Gtk::Window keeps its name.)

5. Gdk::DrawContext and Gdk::CairoContext are new. Gdk::DrawingContext has been removed.

6. Gtk::Clipboard has been replaced by the new Gdk::Clipboard.

7. Gdk::DragContext has been split into Gdk::Drag and Gdk::Drop.

There have also been several changes to the API, which you will probably encounter when porting code that used gtkmm-3.0 and glibmm-2.4. Here is a short list:

1. A C++17 compiler is required.

2. Gtk::Button, Gtk::ToolButton, Gtk::MenuItem and Gtk::Switch implement the Gtk::Actionable interface instead of the removed Gtk::Activatable interface.

3. Gtk::FontButton implements the Gtk::FontChooser interface.

4. Gtk::Widget: The get_preferred_*_vfunc()s have been replaced by measure_vfunc(). This change only affects custom widgets.

5. sigc::slots use the sigc::slot<R(Args...)> syntax. Example: sigc::slot<void(int, int)> instead of sigc::slot<void, int, int>.

6. Gtk::DrawingArea uses a draw function instead of the draw signal.

7. Glib::ArrayHandle, Glib::StringArrayHandle, Glib::ListHandle and Glib::SListHandle have been removed. They were used in glibmm-2.4, but not used in gtkmm-3.0. If you've ever used these classes, replace them with a standard C++ container, such as std::vector.

8. Gtk::Container has been removed.

9. Gtk::Widget::show_all() has been removed. The default value of Gtk::Widget::property_visible() has been changed from `false` to `true`.

10. All event signals have been removed from Gtk::Widget. In most cases you can use one of the subclasses of Gtk::EventController as a replacement. For instance, use Gtk::GestureMultiPress instead of signal_button_press_event() and signal_button_release_event(), and Gtk::EventControllerKey instead of signal_key_press_event() and signal_key_release_event().

11. Glib::RefPtr is an alias for std::shared_ptr. If you make your own Glib::ObjectBase-derived classes with create() methods that return a Glib::RefPtr, you must use Glib::make_refptr_for_instance() in your create() methods.

12. Gtk::Box::pack_start() and Gtk::Box::pack_end() have been removed. Use the new Gtk::Box methods append(), prepend(), insert_child_after() and insert_child_at_start().

13. Gtk::ButtonBox has been removed.

14. Gtk::RadioButton and Gtk::RadioButtonGroup have been removed. Use Gtk::CheckButton or Gtk::ToggleButton with set_group().

All deprecated API was removed in gtkmm 4.0 and glibmm 2.68, though there will be new deprecations in future versions.

As a first step to porting your source code to gtkmm-4.0 you should probably ensure that your application builds with the deprecated gtkmm-3.0 and glibmm-2.4 API disabled, by defining the macros GTKMM_DISABLE_DEPRECATED, GDKMM_DISABLE_DEPRECATED, GLIBMM_DISABLE_DEPRECATED and GIOMM_DISABLE_DEPRECATED. There are some autotools macros that can help with this by defining them optionally at build time. See the Porting from gtkmm-2.4 to gtkmm-3.0 wiki page for more details.

See also Migrating from GTK 3.x to GTK 4.

### Deprecations in gtkmm 4.10

Many classes are deprecated since gtkmm 4.10. They can still be used in gtkmm4 applications, provided GTKMM_DISABLE_DEPRECATED and GDKMM_DISABLE_DEPRECATED are not defined. There are also many new classes in gtkmm 4.10, which replace some of the deprecated classes. Some example programs in this tutorial use classes deprecated since gtkmm 4.10. Some other programs use classes available since gtkmm 4.10.

Deprecated classes: AppChooser, AppChooserButton, AppChooserDialog, AppChooserWidget, CellArea, CellAreaBox, CellAreaContext, CellLayout, CellRenderer, CellRendererAccel, CellRendererCombo, CellRendererPixbuf, CellRendererProgress, CellRendererSpin, CellRendererSpinner, CellRendererText, CellRendererToggle, CellView, ComboBox, ComboBoxText, EntryCompletion, IconView, ListStore, ListViewText, StyleContext, TreeDragDest, TreeDragSource, TreeIter and other classes in treeiter.h, TreeModel, TreeModelFilter, TreeModelSort, TreePath, TreeRowReference, TreeSelection, TreeSortable, TreeStore, TreeView, TreeViewColumn, namespace CellRenderer_Generation, namespace TreeView_Private, ColorButton, ColorChooser, ColorChooserDialog, FileChooser, FileChooserDialog, FileChooserNative, FileChooserWidget, FontButton, FontChooser, FontChooserDialog, FontChooserWidget, MessageDialog, TreeModelColumn, TreeModelColumnRecord, InfoBar, Assistant, AssistantPage, LockButton, Statusbar, VolumeButton.

New classes and enums: AlertDialog, ColorDialog, ColorDialogButton, ColumnViewSorter, FileDialog, FontDialog, FontDialogButton, FileLauncher, UriLauncher, ATContext, enums DialogError, FontLevel, Collation.

In most cases there are replacements for the deprecated classes. See the reference documentation.

## Botões

gtkmm provẽ quatro tipos básicos de botões:

Push buttons

  Gtk::Button. Standard buttons, usually marked with a label or picture. Pushing one triggers an action. See the Button section.

Botões de alternância

  Gtk::ToggleButton. Unlike a normal Button, which springs back up, a ToggleButton stays down until you press it again. It might be useful as an on/off switch. See the ToggleButton section.

Check buttons

  Gtk::CheckButton. These act like ToggleButtons, but show their state in small squares, with their label at the side. They should be used in most situations which require an on/off setting. See the CheckButton section.

Botões de opção

  Named after the station selectors on old car radios, these buttons are used in groups for options which are mutually exclusive. Pressing one causes all the others in its group to turn off. They are similar to ToggleButtons or CheckButtons (a small widget with a label at the side), but usually look different. There is no separate radio button class. Check buttons and toggle buttons can act as radio buttons. See the Radio Button section.

Note that, due to GTK's theming system, the appearance of these widgets will vary. In the case of check buttons and radio buttons, they may vary considerably.

### Botão

Existem duas formas de criar um Botão. Você pode especificar um texto de rótulo no construtor Gtk::Button ou defini-lo mais tarde com set_label().

Para definir uma tecla aceleradora para navegação por teclado, coloque uma sublinha antes de um dos caracteres do rótulo e especifique `true` para o parâmetro opcional `mnemonic`. Por exemplo:

    Gtk::Button* pButton = new Gtk::Button("_Something", true);

Gtk::Button é também um contêiner, então você pode colocar qualquer outro widget nele, como um Gtk::Image.

The Gtk::Button widget has the `clicked` signal which is emitted when the button is pressed and released.

Reference

#### Exemplo

Este exemplo cria um botão com uma figura e um rótulo.

exemplo de botões

Source Code

File: `buttons.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_BUTTONS_H
    #define GTKMM_EXAMPLE_BUTTONS_H

    #include <gtkmm/window.h>
    #include <gtkmm/button.h>

    class Buttons : public Gtk::Window
    {
    public:
      Buttons();
      virtual ~Buttons();

    protected:
      //Signal handlers:
      void on_button_clicked();

      //Child widgets:
      Gtk::Button m_button;
    };

    #endif //GTKMM_EXAMPLE_BUTTONS_H

File: `buttons.cc` (For use with gtkmm 4)

    #include "buttons.h"
    #include <gtkmm/box.h>
    #include <gtkmm/image.h>
    #include <gtkmm/label.h>
    #include <iostream>

    Buttons::Buttons()
    {
      // This corresponds to Gtk::Bin::add_pixlabel("info.xpm", "cool button") in gtkmm3.
      //Create Image and Label widgets:
      auto pmap = Gtk::make_managed<Gtk::Image>("info.xpm");
      auto label = Gtk::make_managed<Gtk::Label>("cool button");
      label->set_expand(true);

      //Put them in a Box:
      auto hbox = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::HORIZONTAL, 5);
      hbox->append(*pmap);
      hbox->append(*label);

      //And put that Box in the button:
      m_button.set_child(*hbox);

      set_title("Pixmap'd buttons!");

      m_button.signal_clicked().connect( sigc::mem_fun(*this,
                  &Buttons::on_button_clicked) );

      m_button.set_margin(10);
      set_child(m_button);
    }

    Buttons::~Buttons()
    {
    }

    void Buttons::on_button_clicked()
    {
      std::cout << "The Button was clicked." << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "buttons.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<Buttons>(argc, argv);
    }

### Botão de alternância

Um ToggleButton é como um Button normal, só que uma vez clicados, eles permanecem ativados, ou pressionados, até que sejam clicados de novo.

para obter o estado do ToggleButton, você pode usar o método get_active(). Ele retorna `true` se o botão está "para baixo". Você também pode definir o estado do botão de alternância, para isso use set_active(). Note que, se você fizer isso e o estado mudar de fato, isso faz com que o sinal `clicked` seja emitido. Isso é o que você quer normalmente.

Você pode usar o método toggled() para alternar o botão, em vez de forçá-lo para cima ou para baixo: isso troca o estado do botão e faz com que o sinal `toggled` seja emitido.

Reference

### Botão de seleção

Gtk::CheckButton inherits directly from Gtk::Widget. It is similar to Gtk::ToggleButton. The only real difference between the two is Gtk::CheckButton's appearance. You can check and set a check button using the same member methods as for Gtk::ToggleButton.

Reference

#### Exemplo

Botão de seleção

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_BUTTONS_H
    #define GTKMM_EXAMPLE_BUTTONS_H

    #include <gtkmm/window.h>
    #include <gtkmm/checkbutton.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_toggled();

      //Child widgets:
      Gtk::CheckButton m_button;
    };

    #endif //GTKMM_EXAMPLE_BUTTONS_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_button("something")
    {
      set_title("checkbutton example");

      m_button.signal_toggled().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_toggled) );

      m_button.set_margin(10);
      set_child(m_button);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_toggled()
    {
      std::cout << "The Button was toggled: state="
          << (m_button.get_active() ? "true" : "false")
          << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Radio Button

There is no separate class for radio buttons. Check buttons and toggle buttons act as radio buttons when they form a group. Only one button in a group can be selected at any one time.

#### Grupos

You create the buttons, and set up their group afterwards. In the following example, we put 3 radio buttons in a group:

    auto rb1 = Gtk::make_managed<Gtk::CheckButton>("button1");
    auto rb2 = Gtk::make_managed<Gtk::CheckButton>("button2");
    auto rb3 = Gtk::make_managed<Gtk::CheckButton>("button3");
    rb2->set_group(*rb1);
    rb3->set_group(*rb1);

We told gtkmm to put all three CheckButtons in the same group by using set_group() to tell the other CheckButtons to share group with the first CheckButton.

#### Métodos

CheckButtons and ToggleButtons are "off" when created; this means that when you first make a group of them, they will all be off. Don't forget to turn one of them on using set_active().

Reference

#### Exemplo

The following example demonstrates the use of grouped CheckButtons:

Botão de opção

Source Code

File: `radiobuttons.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_RADIOBUTTONS_H
    #define GTKMM_EXAMPLE_RADIOBUTTONS_H

    #include <gtkmm/box.h>
    #include <gtkmm/window.h>
    #include <gtkmm/button.h>
    #include <gtkmm/checkbutton.h>
    #include <gtkmm/separator.h>

    class RadioButtons : public Gtk::Window
    {
    public:
      RadioButtons();
      virtual ~RadioButtons();

    protected:
      //Signal handlers:
      void on_button_clicked();

      //Child widgets:
      Gtk::Box m_Box_Top, m_Box1, m_Box2;
      Gtk::CheckButton m_RadioButton1, m_RadioButton2, m_RadioButton3;
      Gtk::Separator m_Separator;
      Gtk::Button m_Button_Close;
    };

    #endif //GTKMM_EXAMPLE_RADIOBUTTONS_H

File: `main.cc` (For use with gtkmm 4)

    #include "radiobuttons.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<RadioButtons>(argc, argv);
    }

File: `radiobuttons.cc` (For use with gtkmm 4)

    #include "radiobuttons.h"

    RadioButtons::RadioButtons() :
      m_Box_Top(Gtk::Orientation::VERTICAL),
      m_Box1(Gtk::Orientation::VERTICAL, 10),
      m_Box2(Gtk::Orientation::VERTICAL, 10),
      m_RadioButton1("button1"),
      m_RadioButton2("button2"),
      m_RadioButton3("button3"),
      m_Button_Close("close")
    {
      // Set title and border of the window
      set_title("radio buttons");

      // Gtk::CheckButton and Gtk::ToggleButton have set_group() methods.
      // They act as radio buttons, if they are included in a group.

      // Put radio buttons 2 and 3 in the same group as 1:
      m_RadioButton2.set_group(m_RadioButton1);
      m_RadioButton3.set_group(m_RadioButton1);

      // Add outer box to the window (because the window
      // can only contain a single widget)
      set_child(m_Box_Top);

      //Put the inner boxes and the separator in the outer box:
      m_Box_Top.append(m_Box1);
      m_Box_Top.append(m_Separator);
      m_Box_Top.append(m_Box2);
      m_Separator.set_expand();

      // Set the inner boxes' margins
      m_Box1.set_margin(10);
      m_Box2.set_margin(10);

      // Put the radio buttons in Box1:
      m_Box1.append(m_RadioButton1);
      m_Box1.append(m_RadioButton2);
      m_Box1.append(m_RadioButton3);
      m_RadioButton1.set_expand();
      m_RadioButton2.set_expand();
      m_RadioButton3.set_expand();

      // Set the second button active
      m_RadioButton2.set_active(true);

      // Put Close button in Box2:
      m_Box2.append(m_Button_Close);
      m_Button_Close.set_expand();

      // Make the button the default widget
      set_default_widget(m_Button_Close);

      // Connect the toggled signal of the button to
      // RadioButtons::on_button_toggled()
      m_Button_Close.signal_clicked().connect(sigc::mem_fun(*this,
                  &RadioButtons::on_button_clicked) );
    }

    RadioButtons::~RadioButtons()
    {
    }

    void RadioButtons::on_button_clicked()
    {
      close();
    }

## Widgets de intervalos

Gtk::Scale inherits from Gtk::Range. Gtk::Scrollbar does not inherit from Gtk::Range, but it shares much functionality with Gtk::Scale. They both contain a "trough" and a "slider" (sometimes called a "thumbwheel" in other GUI environments). Dragging the slider with the pointer moves it within the trough, while clicking in the trough advances the slider towards the location of the click, either completely, or by a designated amount, depending on which mouse button is used. This should be familiar scrollbar behavior.

As will be explained in the Adjustments section, all range widgets are associated with an Adjustment object. To change the lower, upper, and current values used by the widget you need to use the methods of its Adjustment, which you can get with the get_adjustment() method. The range widgets' default constructors create an Adjustment automatically, or you can specify an existing Adjustment, maybe to share it with another widget. See the Adjustments section for further details.

Reference

### Widgets de barra de rolagem

These are standard scrollbars. They should be used only to scroll another widget, such as a Gtk::Entry or a Gtk::Viewport, though it's usually easier to use the Gtk::ScrolledWindow widget in most cases.

A orientação de um Gtk::Scrollbar pode ser horizontal ou vertical.

Reference

### Widgets de escala

Gtk::Scale widgets (or "sliders") allow the user to visually select and manipulate a value within a specific range. You might use one, for instance, to adjust the magnification level on a zoomed preview of a picture, or to control the brightness of a colour, or to specify the number of minutes of inactivity before a screensaver takes over the screen.

As with Scrollbars, the orientation can be either horizontal or vertical. The default constructor creates an Adjustment with all of its values set to `0.0`. This isn't useful so you will need to set some Adjustment details to get meaningful behavior.

#### Métodos úteis

Widgets de Scala pode exibir seu valor atual com um número próximo à calha. Por padrão, eles mostram o valor, você pode mudar isso com o método set_draw_value().

The value displayed by a scale widget is rounded to one decimal point by default, as is the `value` field in its Gtk::Adjustment. You can change this with the set_digits() method.

Além disso, o valor pode ser desenhado em diferentes posições em relação à calha, especificado pelo método set_value_pos().

Reference

### Exemplo

This example displays a window with three range widgets all connected to the same adjustment, along with a couple of controls for adjusting some of the parameters mentioned above and in the section on adjustments, so you can see how they affect the way these widgets work for the user.

Widgets de intervalos

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_RANGEWIDGETS_H
    #define GTKMM_EXAMPLE_RANGEWIDGETS_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_checkbutton_toggled();
      void on_dropdown_position();
      void on_adjustment1_value_changed();
      void on_adjustment2_value_changed();
      void on_button_quit();

      //Child widgets:
      Gtk::Box m_VBox_Top, m_VBox2, m_VBox_HScale;
      Gtk::Box m_HBox_Scales, m_HBox_DropDown, m_HBox_Digits, m_HBox_PageSize;

      Glib::RefPtr<Gtk::Adjustment> m_adjustment, m_adjustment_digits, m_adjustment_pagesize;

      Gtk::Scale m_VScale;
      Gtk::Scale m_HScale, m_Scale_Digits, m_Scale_PageSize;

      Gtk::Separator m_Separator;

      Gtk::CheckButton m_CheckButton;

      Gtk::Scrollbar m_Scrollbar;

      Gtk::DropDown m_DropDown_Position;
      Gtk::Button m_Button_Quit;
    };

    #endif //GTKMM_EXAMPLE_RANGEWIDGETS_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <array>
    #include <iostream>

    namespace
    {
    struct PositionTypeStruct
    {
      Gtk::PositionType position;
      Glib::ustring text;
    };

    const std::array<PositionTypeStruct, 4> positionTypes =
    {
      PositionTypeStruct{Gtk::PositionType::TOP,    "Top"},
      PositionTypeStruct{Gtk::PositionType::BOTTOM, "Bottom"},
      PositionTypeStruct{Gtk::PositionType::LEFT,   "Left"},
      PositionTypeStruct{Gtk::PositionType::RIGHT,  "Right"}
    };

    } // anonymous namespace

    ExampleWindow::ExampleWindow()
    :
      m_VBox_Top(Gtk::Orientation::VERTICAL, 0),
      m_VBox2(Gtk::Orientation::VERTICAL, 20),
      m_VBox_HScale(Gtk::Orientation::VERTICAL, 10),
      m_HBox_Scales(Gtk::Orientation::HORIZONTAL, 10),
      m_HBox_DropDown(Gtk::Orientation::HORIZONTAL, 10),
      m_HBox_Digits(Gtk::Orientation::HORIZONTAL, 10),
      m_HBox_PageSize(Gtk::Orientation::HORIZONTAL, 10),

      // Value, lower, upper, step_increment, page_increment, page_size:
      // Note that the page_size value only makes a difference for
      // scrollbar widgets, and the highest value you'll get is actually
      // (upper - page_size).
      m_adjustment( Gtk::Adjustment::create(0.0, 0.0, 101.0, 0.1, 1.0, 1.0) ),
      m_adjustment_digits( Gtk::Adjustment::create(1.0, 0.0, 5.0, 1.0, 2.0) ),
      m_adjustment_pagesize( Gtk::Adjustment::create(1.0, 1.0, 101.0) ),

      m_VScale(m_adjustment, Gtk::Orientation::VERTICAL),
      m_HScale(m_adjustment, Gtk::Orientation::HORIZONTAL),
      m_Scale_Digits(m_adjustment_digits),
      m_Scale_PageSize(m_adjustment_pagesize),

      // A checkbutton to control whether the value is displayed or not:
      m_CheckButton("Display value on scale widgets", 0),

      // Reuse the same adjustment again.
      // Notice how this causes the scales to always be updated
      // continuously when the scrollbar is moved.
      m_Scrollbar(m_adjustment),

      m_Button_Quit("Quit")
    {
      set_title("range controls");
      set_default_size(300, 350);

      //VScale:
      m_VScale.set_digits(1);
      m_VScale.set_value_pos(Gtk::PositionType::TOP);
      m_VScale.set_draw_value();
      m_VScale.set_inverted(); // highest value at top

      //HScale:
      m_HScale.set_digits(1);
      m_HScale.set_value_pos(Gtk::PositionType::TOP);
      m_HScale.set_draw_value();

      set_child(m_VBox_Top);
      m_VBox_Top.append(m_VBox2);
      m_VBox2.set_expand(true);
      m_VBox2.set_margin(10);
      m_VBox2.append(m_HBox_Scales);
      m_HBox_Scales.set_expand(true);

      //Put VScale and HScale (above scrollbar) side-by-side.
      m_HBox_Scales.append(m_VScale);
      m_VScale.set_expand(true);
      m_HBox_Scales.append(m_VBox_HScale);
      m_VBox_HScale.set_expand(true);

      m_VBox_HScale.append(m_HScale);
      m_HScale.set_expand(true);

      //Scrollbar:
      m_VBox_HScale.append(m_Scrollbar);
      m_Scrollbar.set_expand(true);

      //CheckButton:
      m_CheckButton.set_active();
      m_CheckButton.signal_toggled().connect( sigc::mem_fun(*this,
        &ExampleWindow::on_checkbutton_toggled) );
      m_VBox2.append(m_CheckButton);

      //Position DropDown:
      //Create the StringList:
      auto string_list = Gtk::StringList::create({});
      m_DropDown_Position.set_model(string_list);

      // Fill the DropDown's list model:
      for (const auto& positionType : positionTypes)
        string_list->append(positionType.text);

      m_VBox2.append(m_HBox_DropDown);
      m_HBox_DropDown.append(*Gtk::make_managed<Gtk::Label>("Scale Value Position:", 0));
      m_HBox_DropDown.append(m_DropDown_Position);
      m_DropDown_Position.property_selected().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_dropdown_position));
      m_DropDown_Position.set_selected(0); // Top
      m_DropDown_Position.set_expand(true);

      //Digits:
      m_HBox_Digits.append(*Gtk::make_managed<Gtk::Label>("Scale Digits:", 0));
      m_Scale_Digits.set_digits(0);
      m_Scale_Digits.set_expand(true);
      m_adjustment_digits->signal_value_changed().connect(sigc::mem_fun(*this,
        &ExampleWindow::on_adjustment1_value_changed));
      m_HBox_Digits.append(m_Scale_Digits);

      //Page Size:
      m_HBox_PageSize.append(*Gtk::make_managed<Gtk::Label>("Scrollbar Page Size:", 0));
      m_Scale_PageSize.set_digits(0);
      m_Scale_PageSize.set_expand(true);
      m_adjustment_pagesize->signal_value_changed().connect(sigc::mem_fun(*this,
        &ExampleWindow::on_adjustment2_value_changed));
      m_HBox_PageSize.append(m_Scale_PageSize);

      m_VBox2.append(m_HBox_Digits);
      m_VBox2.append(m_HBox_PageSize);
      m_VBox_Top.append(m_Separator);
      m_VBox_Top.append(m_Button_Quit);

      set_default_widget(m_Button_Quit);
      m_Button_Quit.signal_clicked().connect(sigc::mem_fun(*this,
        &ExampleWindow::on_button_quit));
      m_Button_Quit.set_margin(10);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_checkbutton_toggled()
    {
      m_VScale.set_draw_value(m_CheckButton.get_active());
      m_HScale.set_draw_value(m_CheckButton.get_active());
    }

    void ExampleWindow::on_dropdown_position()
    {
      const auto selected = m_DropDown_Position.get_selected();
      if (selected == GTK_INVALID_LIST_POSITION)
        return;

      const auto postype = positionTypes[selected].position;
      m_VScale.set_value_pos(postype);
      m_HScale.set_value_pos(postype);
    }

    void ExampleWindow::on_adjustment1_value_changed()
    {
      const double val = m_adjustment_digits->get_value();
      m_VScale.set_digits((int)val);
      m_HScale.set_digits((int)val);
    }

    void ExampleWindow::on_adjustment2_value_changed()
    {
      const double val = m_adjustment_pagesize->get_value();
      m_adjustment->set_page_size(val);
      m_adjustment->set_page_increment(val);

      // Note that we don't have to emit the "changed" signal
      // because gtkmm does this for us.
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

## Diversos widgets

### Rótulo

Labels are the main method of placing non-editable text in windows, for instance to place a title next to an Entry widget. You can specify the text in the constructor, or later with the set_text() or set_markup() methods.

The width of the label will be adjusted automatically. You can produce multi-line labels by putting line breaks ("\n") in the label string.

The label text can be justified using the set_justify() method. The widget is also capable of word-wrapping, which can be activated with set_wrap().

Gtk::Label supports some simple formatting, for instance allowing you to make some text bold, colored, or larger. You can do this by providing a string to set_markup(), using the Pango Markup syntax. For instance, `<b>bold text</b> and <s>strikethrough text</s>` .

Reference

#### Exemplo

Below is a short example to illustrate these functions. This example makes use of the Frame widget to better demonstrate the label styles. (The Frame widget is explained in the Frame section.) It is possible that the first character in `m_Label_Normal` is shown underlined only when you press the Alt key.

Rótulo

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:

      //Child widgets:
      Gtk::Box m_HBox;
      Gtk::Box m_VBox, m_VBox2;
      Gtk::Frame m_Frame_Normal, m_Frame_Multi, m_Frame_Left, m_Frame_Right,
        m_Frame_LineWrapped, m_Frame_FilledWrapped, m_Frame_Underlined;
      Gtk::Label m_Label_Normal, m_Label_Multi, m_Label_Left, m_Label_Right,
        m_Label_LineWrapped, m_Label_FilledWrapped, m_Label_Underlined;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    :
      m_HBox(Gtk::Orientation::HORIZONTAL, 5),
      m_VBox(Gtk::Orientation::VERTICAL, 5),
      m_VBox2(Gtk::Orientation::VERTICAL, 5),
      m_Frame_Normal("Normal Label"),
      m_Frame_Multi("Multi-line Label"),
      m_Frame_Left("Left Justified Label"),
      m_Frame_Right("Right Justified Label"),
      m_Frame_LineWrapped("Line wrapped label"),
      m_Frame_FilledWrapped("Filled, wrapped label"),
      m_Frame_Underlined("Underlined label"),
      m_Label_Normal("_This is a Normal label", true),
      m_Label_Multi("This is a Multi-line label.\nSecond line\nThird line"),
      m_Label_Left("This is a Left-Justified\nMulti-line label.\nThird line"),
      m_Label_Right("This is a Right-Justified\nMulti-line label.\nThird line"),
      m_Label_Underlined("<u>This label is underlined!</u>\n"
              "<u>T</u>h<u>is one is</u> <u>u</u>n<u>derlin</u>ed "
              "in<u> q</u>u<u>ite a f</u>u<u>nky</u> fashion")
    {
      set_title("Label");

      m_HBox.set_margin(5);
      set_child(m_HBox);

      m_HBox.append(m_VBox);

      m_Frame_Normal.set_child(m_Label_Normal);
      m_VBox.append(m_Frame_Normal);

      m_Frame_Multi.set_child(m_Label_Multi);
      m_VBox.append(m_Frame_Multi);

      m_Label_Left.set_justify(Gtk::Justification::LEFT);
      m_Frame_Left.set_child(m_Label_Left);
      m_VBox.append(m_Frame_Left);

      m_Label_Right.set_justify(Gtk::Justification::RIGHT);
      m_Frame_Right.set_child(m_Label_Right);
      m_VBox.append(m_Frame_Right);

      m_HBox.append(m_VBox2);

      m_Label_LineWrapped.set_text(
              "This is an example of a line-wrapped label.  It "
              /* add a big space to the next line to test spacing */
              "should not be taking up the entire             "
              "width allocated to it, but automatically "
              "wraps the words to fit.  "
              "The time has come, for all good men, to come to "
              "the aid of their party.  "
              "The sixth sheik's six sheep's sick.\n"
              "     It supports multiple paragraphs correctly, "
              "and  correctly   adds "
              "many          extra  spaces. ");
      m_Label_LineWrapped.set_wrap();
      m_Frame_LineWrapped.set_child(m_Label_LineWrapped);
      m_VBox2.append(m_Frame_LineWrapped);

      m_Label_FilledWrapped.set_text(
              "This is an example of a line-wrapped, filled label.  "
              "It should be taking "
              "up the entire              width allocated to it.  "
              "Here is a sentence to prove "
              "my point.  Here is another sentence. "
              "Here comes the sun, do de do de do.\n"
              "    This is a new paragraph.\n"
              "    This is another newer, longer, better "
              "paragraph.  It is coming to an end, "
              "unfortunately.");
      m_Label_FilledWrapped.set_justify(Gtk::Justification::FILL);
      m_Label_FilledWrapped.set_wrap();
      m_Frame_FilledWrapped.set_child(m_Label_FilledWrapped);
      m_VBox2.append(m_Frame_FilledWrapped);

      m_Label_Underlined.set_justify(Gtk::Justification::LEFT);
      m_Label_Underlined.set_use_markup(true);
      m_Frame_Underlined.set_child(m_Label_Underlined);
      m_VBox2.append(m_Frame_Underlined);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Entrada

#### Uso simples

Campos de entrada permite o usuário digitar texto. Você pode alterar o conteúdo com o método set_text(), e ler o conteúdo atual com o método get_text().

Occasionally you might want to make an Entry widget read-only. This can be done by passing `false` to the set_editable() method.

Para entrada de senhas, frases e outras informações que você não deseja mostrar na tela, chamando set_visibility() com `false` irá fazer com que o texto seja escondido.

You might want to be notified whenever the user types in a text entry widget. Gtk::Entry provides two signals, `activate` (since gtkmm 4.8) and `changed`, for this purpose. `activate` is emitted when the user presses the Enter key in a text-entry widget; `changed` is emitted when the text in the widget changes. You can use these, for instance, to validate or filter the text the user types. Moving the keyboard focus to another widget may also signal that the user has finished entering text. The `leave` signal in a Gtk::EventControllerFocus can notify you when that happens. The ComboBox with an Entry section contains example programs that use these signals.

If you pass `true` to the set_activates_default() method, pressing Enter in the Gtk::Entry will activate the default widget for the window containing the Gtk::Entry. This is especially useful in dialog boxes. The default widget is usually one of the dialog buttons, which e.g. will close the dialog box. To set a widget as the default widget, use Gtk::Window::set_default_widget().

Reference

##### Exemplo de entrada simples

This example uses Gtk::Entry. It also has two CheckButtons, with which you can toggle the editable and visible flags.

Entrada

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_checkbox_editable_toggled();
      void on_checkbox_visibility_toggled();
      void on_button_close();

      //Child widgets:
      Gtk::Box m_HBox;
      Gtk::Box m_VBox;
      Gtk::Entry m_Entry;
      Gtk::Button m_Button_Close;
      Gtk::CheckButton m_CheckButton_Editable, m_CheckButton_Visible;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Close("Close"),
      m_CheckButton_Editable("Editable"),
      m_CheckButton_Visible("Visible")
    {
      set_size_request(200, 100);
      set_title("Gtk::Entry");

      set_child(m_VBox);

      m_Entry.set_max_length(50);
      m_Entry.set_text("hello");
      m_Entry.set_text(m_Entry.get_text() + " world");
      m_Entry.select_region(0, m_Entry.get_text_length());
      m_Entry.set_expand(true);
      m_VBox.append(m_Entry);

      m_VBox.append(m_HBox);

      m_HBox.append(m_CheckButton_Editable);
      m_CheckButton_Editable.set_expand(true);
      m_CheckButton_Editable.signal_toggled().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_checkbox_editable_toggled) );
      m_CheckButton_Editable.set_active(true);

      m_HBox.append(m_CheckButton_Visible);
      m_CheckButton_Visible.set_expand(true);
      m_CheckButton_Visible.signal_toggled().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_checkbox_visibility_toggled) );
      m_CheckButton_Visible.set_active(true);

      m_Button_Close.signal_clicked().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_button_close) );
      m_VBox.append(m_Button_Close);
      m_Button_Close.set_expand();
      set_default_widget(m_Button_Close);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_checkbox_editable_toggled()
    {
      m_Entry.set_editable(m_CheckButton_Editable.get_active());
    }

    void ExampleWindow::on_checkbox_visibility_toggled()
    {
      m_Entry.set_visibility(m_CheckButton_Visible.get_active());
    }

    void ExampleWindow::on_button_close()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Entrada com auto completar

Gtk::EntryCompletion is deprecated since gtkmm 4.10. There is no replacement in gtkmm.

An Entry widget can offer a drop-down list of pre-existing choices based on the first few characters typed by the user. For instance, a search dialog could suggest text from previous searches.

To enable this functionality, you must create an EntryCompletion object, and provide it to the Entry widget via the set_completion() method.

The EntryCompletion may use a TreeModel containing possible entries, specified with set_model(). You should then call set_text_column() to specify which of your model columns should be used to match possible text entries.

Alternatively, if a complete list of possible entries would be too large or too inconvenient to generate, a callback slot may instead be specified with set_match_func(). This is also useful if you wish to match on a part of the string other than the start.

Reference

##### Exemplo de entrada com auto completar

This example creates a Gtk::EntryCompletion and associates it with a Gtk::Entry widget. The completion uses a Gtk::TreeModel of possible entries, and some additional actions.

Entrada com auto completar

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_close();

      //See the comment in the implementation:
      //bool on_completion_match(const Glib::ustring& key, const Gtk::TreeModel::const_iterator& iter);

      //Tree model columns, for the EntryCompletion's filter model:
      class ModelColumns : public Gtk::TreeModel::ColumnRecord
      {
      public:
        ModelColumns()
        { add(m_col_id); add(m_col_name); }

        Gtk::TreeModelColumn<unsigned int> m_col_id;
        Gtk::TreeModelColumn<Glib::ustring> m_col_name;
      };

      ModelColumns m_Columns;

      //Child widgets:
      Gtk::Box m_HBox;
      Gtk::Box m_VBox;
      Gtk::Entry m_Entry;
      Gtk::Label m_Label;
      Gtk::Button m_Button_Close;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Label("Press a or b to see a list of possible completions."),
      m_Button_Close("Close")
    {
      //set_size_request(200, 100);
      set_title("Gtk::EntryCompletion");

      set_child(m_VBox);
      m_VBox.append(m_Entry);

      m_VBox.append(m_Label);
      m_Label.set_expand(true);

      m_Button_Close.signal_clicked().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_button_close) );
      m_VBox.append(m_Button_Close);
      set_default_widget(m_Button_Close);

      //Add an EntryCompletion:
      auto completion =
          Gtk::EntryCompletion::create();
      m_Entry.set_completion(completion);

      //Create and fill the completion's filter model
      auto refCompletionModel =
          Gtk::ListStore::create(m_Columns);
      completion->set_model(refCompletionModel);

      // For more complex comparisons, use a filter match callback, like this.
      // See the comment below for more details:
      //completion->set_match_func( sigc::mem_fun(*this,
                  //&ExampleWindow::on_completion_match) );

      //Fill the TreeView's model
      auto row = *(refCompletionModel->append());
      row[m_Columns.m_col_id] = 1;
      row[m_Columns.m_col_name] = "Alan Zebedee";

      row = *(refCompletionModel->append());
      row[m_Columns.m_col_id] = 2;
      row[m_Columns.m_col_name] = "Adrian Boo";

      row = *(refCompletionModel->append());
      row[m_Columns.m_col_id] = 3;
      row[m_Columns.m_col_name] = "Bob McRoberts";

      row = *(refCompletionModel->append());
      row[m_Columns.m_col_id] = 4;
      row[m_Columns.m_col_name] = "Bob McBob";

      //Tell the completion what model column to use to
      //- look for a match (when we use the default matching, instead of
      //  set_match_func().
      //- display text in the entry when a match is found.
      completion->set_text_column(m_Columns.m_col_name);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_close()
    {
      close();
    }

    /* You can do more complex matching with a handler like this.
     * For instance, you could check for substrings inside the string instead of the start,
     * or you could look for the key in extra model columns as well as the model column that will be displayed.
     * The code here is not actually more complex - it's a reimplementation of the default behaviour.
     *
    bool ExampleWindow::on_completion_match(const Glib::ustring& key, const
            Gtk::TreeModel::const_iterator& iter)
    {
      if(iter)
      {
        const auto row = *iter;

        const auto key_length = key.size();
        auto filter_string = row[m_Columns.m_col_name];

        auto filter_string_start = filter_string.substr(0, key_length);
        //The key is lower-case, even if the user input is not.
        filter_string_start = filter_string_start.lowercase();

        if(key == filter_string_start)
          return true; //A match was found.
      }

      return false; //No match.
    }
    */

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Entrada com ícones

An Entry widget can show an icon at the start or end of the text area. The icon can be specified by methods such as set_icon_from_paintable() or set_icon_from_icon_name(). An application can respond to the user pressing the icon by handling the signal_icon_press signal.

##### Exemplo de entrada com ícones

This example shows a Gtk::Entry widget with a named search icon, and prints text to the terminal when the icon is pressed.

Entrada com ícone

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_icon_pressed(Gtk::Entry::IconPosition icon_pos);
      void on_button_close();

      //Child widgets:
      Gtk::Box m_VBox;
      Gtk::Entry m_Entry;
      Gtk::Button m_Button_Close;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Close("Close")
    {
      set_title("Gtk::Entry");

      set_child(m_VBox);

      m_Entry.set_max_length(50);
      m_Entry.set_text("Hello world");
      m_VBox.append(m_Entry);

      m_Entry.set_icon_from_icon_name("edit-find");
      m_Entry.signal_icon_press().connect( sigc::mem_fun(*this, &ExampleWindow::on_icon_pressed) );

      m_Button_Close.signal_clicked().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_button_close) );
      m_VBox.append(m_Button_Close);
      set_default_widget(m_Button_Close);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_icon_pressed(Gtk::Entry::IconPosition /* icon_pos */)
    {
      std::cout << "Icon pressed." << std::endl;
    }

    void ExampleWindow::on_button_close()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Entrada com barra de progresso

An Entry widget can show a progress bar inside the text area, under the entered text. The progress bar will be shown if the set_progress_fraction() or set_progress_pulse_step() methods are called.

##### Exemplo de entrada com barra de progresso

This example shows a Gtk::Entry widget with a progress bar.

Entrada com barra de progresso

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      bool on_timeout();
      void on_button_close();

      //Child widgets:
      Gtk::Box m_VBox;
      Gtk::Entry m_Entry;
      Gtk::Button m_Button_Close;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Close("Close")
    {
      set_title("Gtk::Entry");

      set_child(m_VBox);

      m_Entry.set_max_length(50);
      m_Entry.set_text("Hello world");
      m_VBox.append(m_Entry);

      //Change the progress fraction every 0.1 second:
      Glib::signal_timeout().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_timeout),
        100
      );

      m_Button_Close.signal_clicked().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_button_close) );
      m_VBox.append(m_Button_Close);
      set_default_widget(m_Button_Close);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    bool ExampleWindow::on_timeout()
    {
      static double fraction = 0;
      m_Entry.set_progress_fraction(fraction);

      fraction += 0.01;
      if(fraction > 1)
        fraction = 0;

      return true;
    }

    void ExampleWindow::on_button_close()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### SpinButton

A SpinButton allows the user to select a value from a range of numeric values. It has an Entry widget with increment and decrement buttons at the side. Clicking the buttons causes the value to 'spin' up and down across the range of possible values. The Entry widget may also be used to enter a value directly.

The value can have an adjustable number of decimal places, and the step size is configurable. SpinButtons have an 'auto-repeat' feature as well: holding down the increment or decrement button can optionally cause the value to change more quickly the longer the button is held down.

SpinButtons use an Adjustment object to hold information about the range of values. These Adjustment attributes are used by the Spin Button like so:

- `value`: value for the Spin Button

- `lower`: lower range value

- `upper`: upper range value

- `step_increment`: value to increment/decrement when pressing mouse button 1

- `page_increment`: value to increment/decrement when pressing mouse button 2

- `page_size`: unused

Além disso, o botão 3 do mouse pode ser usado para ir diretamente aos valores `upper` ou `lower`.

The SpinButton can create a default Adjustment, which you can access via the get_adjustment() method, or you can specify an existing Adjustment in the constructor.

#### Métodos

The number of decimal places can be altered using the set_digits() method.

You can set the spinbutton's value using the set_value() method, and retrieve it with get_value().

The spin() method 'spins' the SpinButton, as if its increment or decrement button had been clicked. You need to specify a Gtk::SpinType to specify the direction or new position.

To prevent the user from typing non-numeric characters into the entry box, pass `true` to the set_numeric() method.

To make the SpinButton 'wrap' between its upper and lower bounds, use the set_wrap() method.

To force it to snap to the nearest `step_increment`, use set_snap_to_ticks().

Reference

#### Exemplo

Here's an example of a SpinButton in action:

SpinButton

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_checkbutton_snap();
      void on_checkbutton_numeric();
      void on_spinbutton_digits_changed();
      void on_button_close();

      enum enumValueFormats
      {
        VALUE_FORMAT_INT,
        VALUE_FORMAT_FLOAT
      };
      void on_button_getvalue(enumValueFormats display);

      //Child widgets:
      Gtk::Frame m_Frame_NotAccelerated, m_Frame_Accelerated;
      Gtk::Box m_HBox_NotAccelerated, m_HBox_Accelerated,
        m_HBox_Buttons;
      Gtk::Box m_VBox_Main, m_VBox, m_VBox_Day, m_VBox_Month, m_VBox_Year,
        m_VBox_Accelerated, m_VBox_Value, m_VBox_Digits;
      Gtk::Label m_Label_Day, m_Label_Month, m_Label_Year,
        m_Label_Value, m_Label_Digits,
        m_Label_ShowValue;
      Glib::RefPtr<Gtk::Adjustment> m_adjustment_day, m_adjustment_month, m_adjustment_year,
        m_adjustment_value, m_adjustment_digits;
      Gtk::SpinButton m_SpinButton_Day, m_SpinButton_Month, m_SpinButton_Year,
        m_SpinButton_Value, m_SpinButton_Digits;
      Gtk::CheckButton m_CheckButton_Snap, m_CheckButton_Numeric;
      Gtk::Button m_Button_Int, m_Button_Float, m_Button_Close;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>
    #include <cstdio>

    ExampleWindow::ExampleWindow()
    :
      m_Frame_NotAccelerated("Not accelerated"),
      m_Frame_Accelerated("Accelerated"),
      m_VBox_Main(Gtk::Orientation::VERTICAL, 5),
      m_VBox(Gtk::Orientation::VERTICAL),
      m_VBox_Day(Gtk::Orientation::VERTICAL),
      m_VBox_Month(Gtk::Orientation::VERTICAL),
      m_VBox_Year(Gtk::Orientation::VERTICAL),
      m_VBox_Accelerated(Gtk::Orientation::VERTICAL),
      m_VBox_Value(Gtk::Orientation::VERTICAL),
      m_VBox_Digits(Gtk::Orientation::VERTICAL),
      m_Label_Day("Day: ", Gtk::Align::START),
      m_Label_Month("Month: ", Gtk::Align::START),
      m_Label_Year("Year: ", Gtk::Align::START),
      m_Label_Value("Value: ", Gtk::Align::START),
      m_Label_Digits("Digits: ", Gtk::Align::START),
      m_adjustment_day( Gtk::Adjustment::create(1.0, 1.0, 31.0, 1.0, 5.0, 0.0) ),
      m_adjustment_month( Gtk::Adjustment::create(1.0, 1.0, 12.0, 1.0, 5.0, 0.0) ),
      m_adjustment_year( Gtk::Adjustment::create(2012.0, 1.0, 2200.0, 1.0, 100.0, 0.0) ),
      m_adjustment_value( Gtk::Adjustment::create(0.0, -10000.0, 10000.0, 0.5, 100.0, 0.0) ),
      m_adjustment_digits( Gtk::Adjustment::create(2.0, 1.0, 5.0, 1.0, 1.0, 0.0) ),
      m_SpinButton_Day(m_adjustment_day),
      m_SpinButton_Month(m_adjustment_month),
      m_SpinButton_Year(m_adjustment_year),
      m_SpinButton_Value(m_adjustment_value, 1.0, 2),
      m_SpinButton_Digits(m_adjustment_digits),
      m_CheckButton_Snap("Snap to 0.5-ticks"),
      m_CheckButton_Numeric("Numeric only input mode"),
      m_Button_Int("Value as Int"),
      m_Button_Float("Value as Float"),
      m_Button_Close("Close")
    {
      set_title("SpinButton");

      m_VBox_Main.set_margin(10);
      set_child(m_VBox_Main);

      m_VBox_Main.append(m_Frame_NotAccelerated);

      m_VBox.set_margin(5);
      m_Frame_NotAccelerated.set_child(m_VBox);

      /* Day, month, year spinners */

      m_VBox.set_spacing(5);
      m_VBox.append(m_HBox_NotAccelerated);

      m_Label_Day.set_expand();
      m_VBox_Day.append(m_Label_Day);

      m_SpinButton_Day.set_wrap();
      m_SpinButton_Day.set_expand();
      m_VBox_Day.append(m_SpinButton_Day);

      m_HBox_NotAccelerated.set_spacing(5);
      m_HBox_NotAccelerated.append(m_VBox_Day);

      m_Label_Month.set_expand();
      m_VBox_Month.append(m_Label_Month);

      m_SpinButton_Month.set_wrap();
      m_SpinButton_Month.set_expand();
      m_VBox_Month.append(m_SpinButton_Month);

      m_HBox_NotAccelerated.append(m_VBox_Month);

      m_Label_Year.set_expand();
      m_VBox_Year.append(m_Label_Year);

      m_SpinButton_Year.set_wrap();
      m_SpinButton_Year.set_expand();
      m_SpinButton_Year.set_size_request(55, -1);
      m_VBox_Year.append(m_SpinButton_Year);

      m_HBox_NotAccelerated.append(m_VBox_Year);

      //Accelerated:
      m_VBox_Main.append(m_Frame_Accelerated);

      m_VBox_Accelerated.set_margin(5);
      m_Frame_Accelerated.set_child(m_VBox_Accelerated);

      m_VBox_Accelerated.set_spacing(5);
      m_VBox_Accelerated.append(m_HBox_Accelerated);

      m_HBox_Accelerated.append(m_VBox_Value);

      m_Label_Value.set_expand();
      m_VBox_Value.append(m_Label_Value);

      m_SpinButton_Value.set_wrap();
      m_SpinButton_Value.set_expand();
      m_SpinButton_Value.set_size_request(100, -1);
      m_VBox_Value.append(m_SpinButton_Value);

      m_HBox_Accelerated.append(m_VBox_Digits);

      m_VBox_Digits.append(m_Label_Digits);
      m_Label_Digits.set_expand();

      m_SpinButton_Digits.set_wrap();
      m_adjustment_digits->signal_value_changed().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_spinbutton_digits_changed) );

      m_VBox_Digits.append(m_SpinButton_Digits);
      m_SpinButton_Digits.set_expand();

      //CheckButtons:
      m_VBox_Accelerated.append(m_CheckButton_Snap);
      m_CheckButton_Snap.set_expand();
      m_CheckButton_Snap.set_active();
      m_CheckButton_Snap.signal_toggled().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_checkbutton_snap) );

      m_VBox_Accelerated.append(m_CheckButton_Numeric);
      m_CheckButton_Numeric.set_expand();
      m_CheckButton_Numeric.set_active();
      m_CheckButton_Numeric.signal_toggled().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_checkbutton_numeric) );

      //Buttons:
      m_VBox_Accelerated.append(m_HBox_Buttons);

      m_Button_Int.signal_clicked().connect( sigc::bind( sigc::mem_fun(*this,
                      &ExampleWindow::on_button_getvalue), VALUE_FORMAT_INT) );
      m_HBox_Buttons.set_spacing(5);
      m_HBox_Buttons.append(m_Button_Int);
      m_Button_Int.set_expand();

      m_Button_Float.signal_clicked().connect( sigc::bind( sigc::mem_fun(*this,
                      &ExampleWindow::on_button_getvalue), VALUE_FORMAT_FLOAT) );
      m_HBox_Buttons.append(m_Button_Float);
      m_Button_Float.set_expand();

      m_VBox_Accelerated.append(m_Label_ShowValue);
      m_Label_ShowValue.set_expand();
      m_Label_ShowValue.set_text("0");

      //Close button:
      m_Button_Close.signal_clicked().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_button_close) );
      m_VBox_Main.append(m_Button_Close);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_close()
    {
      close();
    }

    void ExampleWindow::on_checkbutton_snap()
    {
      m_SpinButton_Value.set_snap_to_ticks( m_CheckButton_Snap.get_active() );
    }

    void ExampleWindow::on_checkbutton_numeric()
    {
      m_SpinButton_Value.set_numeric( m_CheckButton_Numeric.get_active() );
    }

    void ExampleWindow::on_spinbutton_digits_changed()
    {
      m_SpinButton_Value.set_digits( m_SpinButton_Digits.get_value_as_int() );
    }

    void ExampleWindow::on_button_getvalue(enumValueFormats display)
    {
      gchar buf[32];

      if (display == VALUE_FORMAT_INT)
        sprintf (buf, "%d", m_SpinButton_Value.get_value_as_int());
      else
        sprintf (buf, "%0.*f", m_SpinButton_Value.get_digits(),
                m_SpinButton_Value.get_value());

      m_Label_ShowValue.set_text(buf);
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### ProgressBar

Progress bars are used to show the status of an ongoing operation. For instance, a ProgressBar can show how much of a task has been completed.

To change the value shown, use the set_fraction() method, passing a double between 0.0 and 1.0 to provide the new fraction.

A ProgressBar is horizontal and left-to-right by default, but you can change it to a vertical progress bar by using the set_orientation() method.

Reference

#### Modo de atividade

Besides indicating the amount of progress that has occurred, the progress bar can also be used to indicate that there is some activity; this is done by placing the progress bar in activity mode. In this mode, the progress bar displays a small rectangle which moves back and forth. Activity mode is useful in situations where the progress of an operation cannot be calculated as a value range (e.g., receiving a file of unknown length).

To do this, you need to call the pulse() method at regular intervals. You can also choose the step size, with the set_pulse_step() method.

The progress bar can also display a configurable text string next to the bar, using the set_text() method.

#### Exemplo

ProgressBar

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_checkbutton_text();
      void on_checkbutton_activity();
      void on_checkbutton_inverted();

      bool on_timeout();
      void on_button_close();

      //Child widgets:
      Gtk::Box m_VBox;
      Gtk::Grid m_Grid;
      Gtk::ProgressBar m_ProgressBar;
      Gtk::Separator m_Separator;
      Gtk::CheckButton m_CheckButton_Text, m_CheckButton_Activity, m_CheckButton_Inverted;
      Gtk::Button m_Button_Close;

      sigc::connection m_connection_timeout;
      bool m_bActivityMode;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL, 5),
      m_CheckButton_Text("Show text"),
      m_CheckButton_Activity("Activity mode"),
      m_CheckButton_Inverted("Right to Left"),
      m_Button_Close("Close"),
      m_bActivityMode(false)
    {
      set_resizable();
      set_title("Gtk::ProgressBar");

      m_VBox.set_margin(10);
      set_child(m_VBox);

      m_VBox.append(m_ProgressBar);
      m_ProgressBar.set_margin_end(5);
      m_ProgressBar.set_halign(Gtk::Align::CENTER);
      m_ProgressBar.set_valign(Gtk::Align::CENTER);
      m_ProgressBar.set_size_request(100, -1);
      m_ProgressBar.set_text("some text");
      m_ProgressBar.set_show_text(false);

      //Add a timer callback to update the value of the progress bar:
      m_connection_timeout = Glib::signal_timeout().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_timeout), 50 );

      m_VBox.append(m_Separator);
      m_VBox.append(m_Grid);
      m_Grid.set_expand(true);
      m_Grid.set_row_homogeneous(true);

      //Add a check button to select displaying of the trough text:
      m_Grid.attach(m_CheckButton_Text, 0, 0);
      m_CheckButton_Text.set_margin(5);
      m_CheckButton_Text.signal_toggled().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_checkbutton_text) );

      //Add a check button to toggle activity mode:
      m_Grid.attach(m_CheckButton_Activity, 0, 1);
      m_CheckButton_Activity.set_margin(5);
      m_CheckButton_Activity.signal_toggled().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_checkbutton_activity) );

      //Add a check button to select growth from left to right or from right to left:
      m_Grid.attach(m_CheckButton_Inverted, 0, 2);
      m_CheckButton_Inverted.set_margin(5);
      m_CheckButton_Inverted.signal_toggled().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_checkbutton_inverted) );

      //Add a button to exit the program.
      m_VBox.append(m_Button_Close);
      m_Button_Close.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_close) );
      set_default_widget(m_Button_Close);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_checkbutton_text()
    {
      const bool show_text = m_CheckButton_Text.get_active();
      m_ProgressBar.set_show_text(show_text);
    }

    void ExampleWindow::on_checkbutton_activity()
    {
      m_bActivityMode = m_CheckButton_Activity.get_active();

      if(m_bActivityMode)
        m_ProgressBar.pulse();
      else
        m_ProgressBar.set_fraction(0.0);
    }

    void ExampleWindow::on_checkbutton_inverted()
    {
      const bool inverted = m_CheckButton_Inverted.get_active();
      m_ProgressBar.set_inverted(inverted);
    }

    void ExampleWindow::on_button_close()
    {
      close();
    }

    /* Update the value of the progress bar so that we get
     * some movement */
    bool ExampleWindow::on_timeout()
    {
      if(m_bActivityMode)
        m_ProgressBar.pulse();
      else
      {
        double new_val = m_ProgressBar.get_fraction() + 0.01;

        if(new_val > 1.0)
          new_val = 0.0;

        //Set the new value:
        m_ProgressBar.set_fraction(new_val);
      }

      //As this is a timeout function, return true so that it
      //continues to get called
      return true;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### InfoBar

An InfoBar may show small items of information or ask brief questions. Unlike a Dialog, it appears at the top of the current window instead of opening a new window. Its API is very similar to the Gtk::Dialog API.

Reference

#### Exemplo

The InfoBar widget is deprecated since gtkmm 4.10. The example shows an info bar consisting of a Box with a Label and a Button.

InfoBar

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_infobar_ok();
      void on_button_quit();
      void on_button_clear();
      void on_textbuffer_changed();
      void on_parsing_error(const Glib::RefPtr<const Gtk::CssSection>& section,
        const Glib::Error& error);

      void set_infobar_background();

      //Child widgets:
      Gtk::Box m_VBox;

      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::TextView m_TextView;

      Glib::RefPtr<Gtk::TextBuffer> m_refTextBuffer;

      Gtk::Box m_InfoBar;
      Gtk::Label m_Message_Label;
      Gtk::Button m_Button_OK;

      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;
      Gtk::Button m_Button_Clear;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    // The Gtk::InfoBar widget is deprecated since gtk/gtkmm 4.10.
    // A Box with a Label and Button is often a good replacement.
    // If you don't care about its background color, it's even easier
    // than the InfoBar replacement in this example program.

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL, 6),
      m_InfoBar(Gtk::Orientation::HORIZONTAL, 6),
      m_Button_OK("_OK", true),
      m_ButtonBox(Gtk::Orientation::HORIZONTAL, 6),
      m_Button_Quit("_Quit", true),
      m_Button_Clear("_Clear", true)
    {
      set_title("Infobar example");
      set_default_size(400, 200);

      m_VBox.set_margin(6);
      set_child(m_VBox);

      // Add the message label to the InfoBar:
      m_InfoBar.append(m_Message_Label);
      m_Message_Label.set_margin_start(5);
      m_Message_Label.set_hexpand(true);
      m_Message_Label.set_halign(Gtk::Align::START);

      // Add an ok button to the InfoBar:
      m_InfoBar.append(m_Button_OK);
      m_Button_OK.set_margin(5);

      // Add the InfoBar to the vbox:
      m_VBox.append(m_InfoBar);

      // Create the buffer and set it for the TextView:
      m_refTextBuffer = Gtk::TextBuffer::create();
      m_TextView.set_buffer(m_refTextBuffer);

      // Add the TextView, inside a ScrolledWindow:
      m_ScrolledWindow.set_child(m_TextView);

      // Show the scrollbars only when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);

      // Add button box:
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Clear);
      m_ButtonBox.append(m_Button_Quit);
      m_Button_Clear.set_hexpand(true);
      m_Button_Clear.set_halign(Gtk::Align::END);

      // Connect signals:
      m_Button_OK.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_infobar_ok) );
      m_Button_Quit.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_quit) );
      m_Button_Clear.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_clear) );
      m_refTextBuffer->signal_changed().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_textbuffer_changed) );

      // Keep the InfoBar hidden until a message needs to be shown:
      m_InfoBar.set_visible(false);
      set_infobar_background();

      // Make the clear button insensitive until text is typed in the buffer.  When
      // the button is sensitive and it is pressed, the InfoBar is displayed with a
      // message.
      m_Button_Clear.set_sensitive(false);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_infobar_ok()
    {
      // Clear the message and hide the info bar:
      m_Message_Label.set_text("");
      m_InfoBar.set_visible(false);
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void ExampleWindow::on_button_clear()
    {
      m_refTextBuffer->set_text("");
      m_Message_Label.set_text("Cleared the text.");
      m_InfoBar.set_visible(true);
    }

    void ExampleWindow::on_textbuffer_changed()
    {
      m_Button_Clear.set_sensitive(m_refTextBuffer->size() > 0);
    }

    void ExampleWindow::set_infobar_background()
    {
      // Concerning color in CSS files, see https://www.w3.org/TR/css-color-3.
      const std::string css = "#infobarbox { background-color: beige; }";

      m_InfoBar.set_name("infobarbox");
      auto css_provider = Gtk::CssProvider::create();
      Gtk::StyleProvider::add_provider_for_display(
        m_InfoBar.get_display(), css_provider, GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);

      css_provider->load_from_data(css);
      css_provider->signal_parsing_error().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_parsing_error));
    }

    void ExampleWindow::on_parsing_error(const Glib::RefPtr<const Gtk::CssSection>& section,
      const Glib::Error& error)
    {
      std::cerr << "on_parsing_error(): " << error.what() << std::endl;
      if (section)
      {
        const auto file = section->get_file();
        if (file)
        {
          std::cerr << "  URI = " << file->get_uri() << std::endl;
        }

        auto start_location = section->get_start_location();
        auto end_location = section->get_end_location();
        std::cerr << "  start_line = " << start_location.get_lines()+1
                  << ", end_line = " << end_location.get_lines()+1 << std::endl;
        std::cerr << "  start_position = " << start_location.get_line_chars()
                  << ", end_position = " << end_location.get_line_chars() << std::endl;
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Dicas

Tooltips are the little information windows that pop up when you leave your pointer over a widget for a few seconds. Use set_tooltip_text() to set a text string as a tooltip on any Widget. Gtk::Tooltip is used for more advanced tooltip usage, such as showing an image as well as text.

Widget Reference

Tooltip Reference

#### Exemplo

Dica de Ferramenta

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:

      ExampleWindow();
      virtual ~ExampleWindow();

    protected:

      //Methods:
      void prepare_textview();
      void connect_signals();

      //Signal handlers:
      void on_markup_checkbutton_toggled();
      bool on_textview_query_tooltip(int x, int y, bool keyboard_tooltip, const Glib::RefPtr<Gtk::Tooltip>& tooltip);
      bool on_button_query_tooltip(int x, int y, bool keyboard_tooltip, const Glib::RefPtr<Gtk::Tooltip>& tooltip);

      //Child widgets:
      Gtk::Box m_vbox;

      Gtk::CheckButton m_checkbutton;
      Gtk::Label m_label;

      Gtk::ScrolledWindow m_scrolled_window;
      Gtk::TextView m_text_view;
      Glib::RefPtr<Gtk::TextBuffer> m_ref_text_buffer;
      Glib::RefPtr<Gtk::TextTag> m_ref_bold_tag;

      Gtk::Button m_button;
      Gtk::Box m_button_tooltip_widget;
    };

    #endif // GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <vector>

    const Glib::ustring app_title = "gtkmm tooltips example";
    const Glib::ustring non_markedup_tip = "A tooltip without markup.";
    const Glib::ustring markedup_tip = "<i>Markup</i> in a tooltip.";

    ExampleWindow::ExampleWindow()
      :
      m_vbox(Gtk::Orientation::VERTICAL, 3),
      m_checkbutton("Click to alternate markup in tooltip"),
      m_label("A label"),
      m_button("Button with a custom tooltip widget")
    {
      //Set up window and the top-level container:
      set_title(app_title);

      m_vbox.set_margin(10);
      set_child(m_vbox);

      //Check button with markup in tooltip:
      m_checkbutton.set_tooltip_text(non_markedup_tip);
      m_vbox.append(m_checkbutton);

      //Label:
      m_label.set_tooltip_text("Another tooltip");
      m_vbox.append(m_label);

      //Textview:
      prepare_textview();

      //Button:
      //When only connecting to the query-tooltip signal, and not using any
      //of set_tooltip_text() or set_tooltip_markup(), we need to explicitly
      //tell GTK that the widget has a tooltip which we'll show.
      m_button.set_has_tooltip();
      m_vbox.append(m_button);

      //Button's custom tooltip widget:
      auto label = Gtk::make_managed<Gtk::Label>("A label in a custom tooltip widget");
      m_button_tooltip_widget.append(*label);

      connect_signals();
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::prepare_textview()
    {
      Gtk::TextIter iter;
      std::vector<Glib::RefPtr<Gtk::TextTag>> tags;

      //Set up a scrolled window:
      m_scrolled_window.set_child(m_text_view);
      m_scrolled_window.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_scrolled_window.set_expand();
      m_vbox.append(m_scrolled_window);

      //Create a text buffer with some text:
      m_ref_text_buffer = Gtk::TextBuffer::create();

      iter = m_ref_text_buffer->end();
      m_ref_text_buffer->insert(iter, "Hover over the text ");

      //Insert some text with a tag.
      //In the tooltip signal handler below, we will show a tooltip
      //when mouse pointer is above this tagged text.
      m_ref_bold_tag = m_ref_text_buffer->create_tag("bold");
      m_ref_bold_tag->set_property("weight", Pango::Weight::BOLD);

      tags.push_back(m_ref_bold_tag);

      iter = m_ref_text_buffer->end();
      m_ref_text_buffer->insert_with_tags(iter, "in bold", tags);

      iter = m_ref_text_buffer->end();
      m_ref_text_buffer->insert(iter, " to see its tooltip");

      m_text_view.set_buffer(m_ref_text_buffer);

      m_text_view.set_size_request(320, 50);

      //When only connecting to the query-tooltip signal, and not using any
      //of set_tooltip_text() or set_tooltip_markup(), we need to explicitly
      //tell GTK that the widget has a tooltip which we'll show.
      m_text_view.set_has_tooltip();
    }

    void ExampleWindow::connect_signals()
    {
      m_checkbutton.signal_toggled().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_markup_checkbutton_toggled));

      m_text_view.signal_query_tooltip().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_textview_query_tooltip), true);

      m_button.signal_query_tooltip().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_query_tooltip), true);
    }

    void ExampleWindow::on_markup_checkbutton_toggled()
    {
      if (m_checkbutton.get_active())
      {
        m_checkbutton.set_tooltip_markup(markedup_tip);
      }
      else
      {
        m_checkbutton.set_tooltip_markup(non_markedup_tip);
      }
    }

    bool ExampleWindow::on_textview_query_tooltip(int x, int y, bool keyboard_tooltip, const Glib::RefPtr<Gtk::Tooltip>& tooltip)
    {
      Gtk::TextIter iter;

      if (keyboard_tooltip)
      {
        int offset = m_ref_text_buffer->property_cursor_position().get_value();
        iter = m_ref_text_buffer->get_iter_at_offset(offset);
      }
      else
      {
        int mouse_x, mouse_y, trailing;
        m_text_view.window_to_buffer_coords(Gtk::TextWindowType::TEXT,
                                            x, y, mouse_x, mouse_y);
        m_text_view.get_iter_at_position(iter, trailing, mouse_x, mouse_y);
      }

      if (!iter.has_tag(m_ref_bold_tag))
        return false;

      //Show a tooltip if the cursor or mouse pointer is over the text
      //with the specific tag:
      tooltip->set_markup("<b>Information</b> attached to a text tag");
      tooltip->set_icon("dialog-information");
      return true;
    }

    bool ExampleWindow::on_button_query_tooltip(int, int, bool, const Glib::RefPtr<Gtk::Tooltip>& tooltip)
    {
      tooltip->set_custom(m_button_tooltip_widget);
      return true;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

## Widgets de empacotamento

Container widgets, like other widgets, derive from Gtk::Widget. Some container widgets, such as Gtk::Grid can hold many child widgets, so these typically have more complex interfaces. Others, such as Gtk::Frame contain only one child widget.

### Empacotamento de item único

Most single-item container widgets have set_child() and unset_child() methods for the child widget. Gtk::Button and Gtk::Window are technically single-item containers, but we have discussed them already elsewhere.

We also discuss the Gtk::Paned widget, which allows you to divide a window into two separate "panes". This widget actually contains two child widgets, but the number is fixed so it seems appropriate.

#### Moldura

Frames can enclose one or a group of widgets within a box, optionally with a title. For instance, you might place a group of ToggleButtons or CheckButtons in a Frame.

Reference

##### Exemplo

Moldura

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:

      //Child widgets:
      Gtk::Frame m_Frame;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    {
     /* Set some window properties */
      set_title("Frame Example");
      set_size_request(300, 300);

      /* Sets the margin around the frame. */
      m_Frame.set_margin(10);

      set_child(m_Frame);

      /* Set the frames label */
      m_Frame.set_label("Gtk::Frame Widget");

      /* Align the label at the right of the frame */
      m_Frame.set_label_align(Gtk::Align::END);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Painel

Panes divide a widget into two halves, separated by a moveable divider. The two halves (panes) can be oriented either horizontally (side by side) or vertically (one above the other).

Unlike the other widgets in this section, pane widgets contain not one but two child widgets, one in each pane. Therefore, you should use set_start_child() and set_end_child() instead of a set_child() method.

You can adjust the position of the divider using the set_position() method, and you will probably need to do so.

Reference

##### Exemplo

Painel

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include "messageslist.h"
    #include "messagetext.h"
    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:

      //Child widgets:
      Gtk::Paned m_VPaned;
      MessagesList m_MessagesList;
      MessageText m_MessageText;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `messageslist.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_MESSAGESLIST_H
    #define GTKMM_EXAMPLE_MESSAGESLIST_H

    #include <gtkmm.h>

    class MessagesList: public Gtk::ScrolledWindow
    {
    public:
      MessagesList();
      ~MessagesList() override;

    protected:
      // Signal handlers:
      void on_setup_message(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_message(const Glib::RefPtr<Gtk::ListItem>& list_item);

      Glib::RefPtr<Gtk::StringList> m_refStringList; // The List Model.
      Gtk::ListView m_ListView; // The List View.
    };
    #endif //GTKMM_EXAMPLE_MESSAGESLIST_H

File: `messagetext.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_MESSAGETEXT_H
    #define GTKMM_EXAMPLE_MESSAGETEXT_H

    #include <gtkmm.h>

    class MessageText : public Gtk::ScrolledWindow
    {
    public:
      MessageText();
      virtual ~MessageText();

      void insert_text();

    protected:
      Gtk::TextView m_TextView;
    };

    #endif //GTKMM_EXAMPLE_MESSAGETEXT_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VPaned(Gtk::Orientation::VERTICAL)
    {
      set_title ("Paned Windows");
      set_default_size(450, 400);
      m_VPaned.set_margin(10);

      /* Add a vpaned widget to our toplevel window */
      set_child(m_VPaned);

      /* Now add the contents of the two halves of the window */
      m_VPaned.set_start_child(m_MessagesList);
      m_VPaned.set_end_child(m_MessageText);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `messageslist.cc` (For use with gtkmm 4)

    #include "messageslist.h"

    MessagesList::MessagesList()
    {
      /* Create a new scrolled window, with scrollbars only if needed */
      set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);

      set_child(m_ListView);

      /* create list store */
      m_refStringList = Gtk::StringList::create({});
      auto selection_model = Gtk::SingleSelection::create(m_refStringList);
      m_ListView.set_model(selection_model);

      /* Add some messages to the window */
      for (int i = 1; i <= 10; ++i)
        m_refStringList->append(Glib::ustring::format("message #", i));

      // Create a ListItemFactory to use for populating list items.
      auto factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(sigc::mem_fun(*this, &MessagesList::on_setup_message));
      factory->signal_bind().connect(sigc::mem_fun(*this, &MessagesList::on_bind_message));
      m_ListView.set_factory(factory);
    }

    MessagesList::~MessagesList()
    {
    }

    void MessagesList::on_setup_message(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto label = Gtk::make_managed<Gtk::Label>();
      label->set_halign(Gtk::Align::START);
      list_item->set_child(*label);
    }

    void MessagesList::on_bind_message(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto pos = list_item->get_position();
      if (pos == GTK_INVALID_LIST_POSITION)
        return;
      auto label = dynamic_cast<Gtk::Label*>(list_item->get_child());
      if (!label)
        return;
      label->set_text(m_refStringList->get_string(pos));
    }

File: `messagetext.cc` (For use with gtkmm 4)

    #include "messagetext.h"

    MessageText::MessageText()
    {
      set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);

      set_child(m_TextView);
      insert_text();
    }

    MessageText::~MessageText()
    {
    }

    void MessageText::insert_text()
    {
      auto refTextBuffer = m_TextView.get_buffer();

      auto iter = refTextBuffer->get_iter_at_offset(0);
      refTextBuffer->insert(iter,
        "From: pathfinder@nasa.gov\n"
        "To: mom@nasa.gov\n"
        "Subject: Made it!\n"
        "\n"
        "We just got in this morning. The weather has been\n"
        "great - clear but cold, and there are lots of fun sights.\n"
        "Sojourner says hi. See you soon.\n"
        " -Path\n");
    }

#### ScrolledWindow

ScrolledWindow widgets create a scrollable area. You can insert any type of widget into a ScrolledWindow, and it will be accessible regardless of its size by using the scrollbars. Note that ScrolledWindow is not a Gtk::Window despite the slightly misleading name.

Scrolled windows have scrollbar policies which determine whether the Scrollbars will be displayed. The policies can be set with the set_policy() method. The policy may be for instance `Gtk::PolicyType::AUTOMATIC` or `Gtk::PolicyType::ALWAYS`. `Gtk::PolicyType::AUTOMATIC` will cause the scrolled window to display the scrollbar only if the contained widget is larger than the visible area. `Gtk::PolicyType::ALWAYS` will cause the scrollbar to be displayed always.

Reference

##### Exemplo

Here is a simple example that packs 100 toggle buttons into a ScrolledWindow. Try resizing the window to see the scrollbars react.

ScrolledWindow

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_button_close();

      //Child widgets:
      Gtk::Box m_VBox;
      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::Grid m_Grid;
      Gtk::Button m_ButtonClose;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL, 10),
      m_ButtonClose("_Close", true)
    {
      set_title("Gtk::ScrolledWindow example");
      set_size_request(300, 300);

      set_child(m_VBox);
      m_VBox.set_margin(10);

      /* The policy is one of Gtk::PolicyType::AUTOMATIC, or Gtk::PolicyType::ALWAYS.
       * Gtk::PolicyType::AUTOMATIC will automatically decide whether you need
       * scrollbars, whereas Gtk::PolicyType::ALWAYS will always leave the scrollbars
       * there. The first one is the horizontal scrollbar, the second, the vertical. */
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::ALWAYS);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);

      /* set the spacing to 10 on x and 10 on y */
      m_Grid.set_row_spacing(10);
      m_Grid.set_column_spacing(10);

      /* pack the grid into the scrolled window */
      m_ScrolledWindow.set_child(m_Grid);

      /* this simply creates a grid of toggle buttons
       * to demonstrate the scrolled window. */
      for (int i = 0; i < 10; i++)
      {
        for (int j = 0; j < 10; j++)
        {
          auto s = Glib::ustring::compose("button (%1,%2)", i, j);
          auto pButton = Gtk::make_managed<Gtk::ToggleButton>(s);
          m_Grid.attach(*pButton, i, j);
        }
      }

      /* Add a "close" button to the bottom of the dialog */
      m_VBox.append(m_ButtonClose);
      m_ButtonClose.set_halign(Gtk::Align::END);
      m_ButtonClose.signal_clicked().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_close));

      /* Hitting the "Enter" key will cause this button to activate. */
      m_ButtonClose.grab_focus();
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_close()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### AspectFrame

The AspectFrame widget looks like a Frame widget, but it also enforces the aspect ratio (the ratio of the width to the height) of the child widget, adding extra space if necessary. For instance, this would allow you to display a photograph without allowing the user to distort it horizontally or vertically while resizing.

Reference

##### Exemplo

The following program uses a Gtk::AspectFrame to present a drawing area whose aspect ratio will always be 2:1, no matter how the user resizes the top-level window.

AspectFrame

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:

      //Child widgets:
      Gtk::AspectFrame m_AspectFrame;
      Gtk::Frame m_Frame;
      Gtk::DrawingArea m_DrawingArea;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_AspectFrame(
        Gtk::Align::CENTER, /* center x */
        Gtk::Align::CENTER, /* center y */
        2.0, /* xsize/ysize = 2 */
        false /* ignore child's aspect */),
      m_Frame("2x1" /* label */)
    {
      set_title("Aspect Frame");

      // Set a child widget to the aspect frame */
      // Ask for a 200x200 window, but the AspectFrame will give us a 200x100
      // window since we are forcing a 2x1 aspect ratio */
      m_DrawingArea.set_content_width(200);
      m_DrawingArea.set_content_height(200);
      m_Frame.set_child(m_DrawingArea);
      m_AspectFrame.set_child(m_Frame);
      m_AspectFrame.set_margin(10);

      // Add the aspect frame to our toplevel window:
      set_child(m_AspectFrame);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Other Single-item Containers

There are other single-item containers. See the reference documentation for a complete list. Here are links to some example programs that show containers, which are not mentioned elsewhere in this tutorial.

Source Code, Expander

Source Code, Popover

### Multiple-item Containers

Multiple-item container widgets have other methods than set_child() and unset_child(). Different containers can have different methods for adding and removing child widgets. For instance, Gtk::Box has append() and remove() as well as other methods. The remove() method for multiple-item containers takes an argument, specifying which widget to remove.

#### Packing

You've probably noticed that gtkmm windows seem "elastic" - they can usually be stretched in many different ways. This is due to the widget packing system.

Many GUI toolkits require you to precisely place widgets in a window, using absolute positioning, often using a visual editor. This leads to several problems:

- The widgets don't rearrange themselves when the window is resized. Some widgets are hidden when the window is made smaller, and lots of useless space appears when the window is made larger.

- It's impossible to predict the amount of space necessary for text after it has been translated to other languages, or displayed in a different font. On Unix it is also impossible to anticipate the effects of every theme and window manager.

- Changing the layout of a window "on the fly", to make some extra widgets appear, for instance, is complex. It requires tedious recalculation of every widget's position.

gtkmm uses the packing system to solve these problems. Rather than specifying the position and size of each widget in the window, you can arrange your widgets in rows, columns, and/or grids. gtkmm can size your window automatically, based on the sizes of the widgets it contains. And the sizes of the widgets are, in turn, determined by the amount of text they contain, or the minimum and maximum sizes that you specify, and/or how you have requested that the available space should be shared between sets of widgets. You can perfect your layout by specifying margins and centering values for each of your widgets. gtkmm then uses all this information to resize and reposition everything sensibly and smoothly when the user manipulates the window.

gtkmm arranges widgets hierarchically, using containers. A container widget contains other widgets. Most gtkmm widgets are containers. Windows, Notebook tabs, and Buttons are all container widgets. There are two flavors of containers: single-child containers and multiple-child containers. Most container widgets in gtkmm are single-child containers, including Gtk::Window.

Yes, that's correct: a Window can contain at most one widget. How, then, can we use a window for anything useful? By placing a multiple-child container in the window. The most useful container widgets are Gtk::Grid and Gtk::Box.

- Gtk::Grid arranges its child widgets in rows and columns. Use attach() and attach_next_to() to insert child widgets.

- Gtk::Box arranges its child widgets vertically or horizontally. Use append() to insert child widgets.

There are several other containers, which we will also discuss.

If you've never used a packing toolkit before, it can take some getting used to. You'll probably find, however, that you don't need to rely on visual form editors quite as much as you might with other toolkits.

#### Um olá mundo melhorado

Let's take a look at a slightly improved `helloworld`, showing what we've learnt.

Olá, mundo 2

Source Code

File: `helloworld.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_HELLOWORLD_H
    #define GTKMM_EXAMPLE_HELLOWORLD_H

    #include <gtkmm/box.h>
    #include <gtkmm/button.h>
    #include <gtkmm/window.h>

    class HelloWorld : public Gtk::Window
    {
    public:
      HelloWorld();
      ~HelloWorld() override;

    protected:

      // Signal handlers:
      // Our new improved on_button_clicked().
      void on_button_clicked(const Glib::ustring& data);

      // Child widgets:
      Gtk::Box m_box1;
      Gtk::Button m_button1, m_button2;
    };

    #endif // GTKMM_EXAMPLE_HELLOWORLD_H

File: `helloworld.cc` (For use with gtkmm 4)

    #include "helloworld.h"
    #include <iostream>

    HelloWorld::HelloWorld()
    : m_button1("Button 1"),
      m_button2("Button 2")
    {
      // This just sets the title of our new window.
      set_title("Hello Buttons!");

      // Sets the margin around the box.
      m_box1.set_margin(10);

      // put the box into the main window.
      set_child(m_box1);

      // Now when the button is clicked, we call the on_button_clicked() function
      // with a pointer to "button 1" as its argument.
      m_button1.signal_clicked().connect(sigc::bind(
                  sigc::mem_fun(*this, &HelloWorld::on_button_clicked), "button 1"));

      // We use Gtk::Box::append() to pack this button into the box,
      // which has been packed into the window.
      // A widget's default behaviour is not to expand if extra space is available.
      // A container widget by default expands if any of the contained widgets
      // wants to expand.
      m_box1.append(m_button1);
      m_button1.set_expand();

      // call the same signal handler with a different argument,
      // passing a pointer to "button 2" instead.
      m_button2.signal_clicked().connect(sigc::bind(
                  sigc::mem_fun(*this, &HelloWorld::on_button_clicked), "button 2"));

      m_box1.append(m_button2);
      m_button2.set_expand();

      // Gtk::Widget::set_visible(true) is seldom needed. All widgets are visible by default.
    }

    HelloWorld::~HelloWorld()
    {
    }

    // Our new improved signal handler.  The data passed to this method is
    // printed to stdout.
    void HelloWorld::on_button_clicked(const Glib::ustring& data)
    {
      std::cout << "Hello World - " << data << " was pressed" << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "helloworld.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<HelloWorld>(argc, argv);
    }

After building and running this program, try resizing the window to see the behavior. Also, try playing with set_expand(), set_hexpand(), set_vexpand(), set_halign() and set_valign() while reading the Boxes section.

#### Caixas

Most packing uses boxes as in the above example. These are invisible containers into which we can pack our widgets. When packing widgets into a horizontal box, the objects are inserted horizontally from left to right. In a vertical box, widgets are packed from top to bottom. You may use any combination of boxes inside or beside other boxes to create the desired effect.

##### Adicionando widgets

###### Opções de empacotamento por filhos

The append() method places widgets inside these containers. It will start at the top and work its way down in a Box with vertical orientation, or pack left to right in a Box with horizontal orientation. If it's inconvenient to add widgets in this order, use insert_child_after() or insert_child_at_start(). We will use append() in our examples.

There are several options governing how widgets are to be packed, and this can be confusing at first. You can modify the packing by using set_expand(), set_hexpand(), set_vexpand(), set_halign(), set_valign() and/or set_margin() on the child widgets. If you have difficulties, then it is sometimes a good idea to play with the Cambalache GUI designer to see what is possible. You can then use the Gtk::Builder API to load your GUI at runtime.

There are basically five different styles, as shown in this picture:

Box Packing 1

Each line contains one horizontal Box with several buttons. Each of the buttons on a line is packed into the Box with the same arguments to the set_hexpand(), set_halign(), set_margin_start() and set_margin_end() methods.

Reference

###### Opções de empacotamento por recipiente

Here's the constructor for the Box widget, and methods that set per-container packing options:

    Gtk::Box(Gtk::Orientation orientation = Gtk::Orientation::HORIZONTAL, int spacing = 0);
    void set_orientation(Gtk::Orientation orientation);
    void set_spacing(int spacing);
    void set_homogeneous(bool homogeneous = true);

Passing `true` to set_homogeneous() will cause all of the contained widgets to be the same size. spacing is a (minimum) number of pixels to leave between each widget.

What's the difference between spacing (set when the box is created) and margins (set separately for each child widget)? Spacing is added between objects, and margins are added on one or more sides of a widget. The following figure should make it clearer. The shown margins are the left and right margins of each button in the row.

Caixa de embalagem 2

##### Gtk::Application e opções de linha de comando

O programa de exemplo a seguir exige uma opção de linha de comando. O código fonte mostra duas maneiras de lidar com linhas de comando em combinação com Gtk::Application.

- Handle the options in `main()` and hide them from Gtk::Application by setting `argc = 1` in the call to Gtk::Application::run().

- Give all command-line options to Gtk::Application::run() and add the flag `Gio::Application::Flags::HANDLES_COMMAND_LINE` to Gtk::Application::create(). Connect a signal handler to the `command_line` signal, and handle the command-line options in the signal handler.

  You must set the optional parameter `after = false` in the call to `signal_command_line().connect()`, because your signal handler must be called before the default signal handler. You must also call Gio::Application::activate() in the signal handler, unless you want your application to exit without showing its main window. (Gio::Application is a base class of Gtk::Application.)

##### Exemplo

Aqui está o código fonte para o exemplo que produziu as imagens acima. Quando você executar esse exemplo, fornecer um número entre 1 e 3 como uma opção de linha de comando, para ver diferentes opções de empacotamento em uso.

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow(int which);
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_quit_clicked();

      //Child widgets:
      Gtk::Button m_button;
      Gtk::Box m_box1;
      Gtk::Box m_boxQuit;
      Gtk::Button m_buttonQuit;

      Gtk::Label m_Label1, m_Label2;

      Gtk::Separator m_separator1, m_separator2;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `packbox.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_PACKBOX_H
    #define GTKMM_EXAMPLE_PACKBOX_H

    #include <gtkmm.h>

    class PackBox : public Gtk::Box
    {
    public:
      PackBox(bool homogeneous = false, int spacing = 0, bool expand = false,
        Gtk::Align align = Gtk::Align::FILL, int margin = 0);

    protected:
      Gtk::Button m_buttons[4];
    };

    #endif //GTKMM_EXAMPLE_PACKBOX_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include <iostream>
    #include "examplewindow.h"
    #include "packbox.h"

    ExampleWindow::ExampleWindow(int which)
    : m_box1(Gtk::Orientation::VERTICAL),
      m_buttonQuit("Quit")
    {
      set_title("Gtk::Box example");

      m_separator1.set_margin_top(5);
      m_separator1.set_margin_bottom(5);
      m_separator2.set_margin_top(5);
      m_separator2.set_margin_bottom(5);

      switch(which)
      {
        case 1:
        {
          m_Label1.set_text("Gtk::Box(Gtk::Orientation::HORIZONTAL, 0); set_homogeneous(false);");

          // Align the label to the left side.
          m_Label1.set_halign(Gtk::Align::START);
          m_Label1.set_valign(Gtk::Align::START);

          // Pack the label into the vertical box (vbox box1).  Remember that
          // widgets added to a vbox will be packed one on top of the other in
          // order.
          m_box1.append(m_Label1);

          // Create a PackBox - homogeneous = false, spacing = 0,
          // expand = false, Gtk::Align::FILL, margin = 0
          // These are the default values.
          auto pPackBox = Gtk::make_managed<PackBox>();
          m_box1.append(*pPackBox);

          // Create a PackBox - homogeneous = false, spacing = 0,
          // expand = true, Gtk::Align::CENTER, margin = 0
          pPackBox = Gtk::make_managed<PackBox>(false, 0, true, Gtk::Align::CENTER);
          m_box1.append(*pPackBox);

          // Create a PackBox - homogeneous = false, spacing = 0,
          // expand = true, Gtk::Align::FILL, margin = 0
          pPackBox = Gtk::make_managed<PackBox>(false, 0, true);
          m_box1.append(*pPackBox);

          // pack the separator into the vbox.  Remember each of these
          // widgets are being packed into a vbox, so they'll be stacked
          // vertically.
          m_box1.append(m_separator1);

          // create another new label, and show it.
          m_Label2.set_text("Gtk::Box(Gtk::Orientation::HORIZONTAL, 0); set_homogeneous(true);");
          m_Label2.set_halign(Gtk::Align::START);
          m_Label2.set_valign(Gtk::Align::START);
          m_box1.append(m_Label2);

          // Args are: homogeneous, spacing, expand, align, margin
          pPackBox = Gtk::make_managed<PackBox>(true, 0, true, Gtk::Align::CENTER);
          m_box1.append(*pPackBox);

          // Args are: homogeneous, spacing, expand, align, margin
          pPackBox = Gtk::make_managed<PackBox>(true, 0, true);
          m_box1.append(*pPackBox);

          m_box1.append(m_separator2);

          break;
        }

        case 2:
        {
          m_Label1.set_text("Gtk::Box(Gtk::Orientation::HORIZONTAL, 10); set_homogeneous(false);");
          m_Label1.set_halign(Gtk::Align::START);
          m_Label1.set_valign(Gtk::Align::START);
          m_box1.append(m_Label1);

          auto pPackBox = Gtk::make_managed<PackBox>(false, 10, true, Gtk::Align::CENTER);
          m_box1.append(*pPackBox);

          pPackBox = Gtk::make_managed<PackBox>(false, 10, true);
          m_box1.append(*pPackBox);

          m_box1.append(m_separator1);

          m_Label2.set_text("Gtk::Box(Gtk::Orientation::HORIZONTAL, 0); set_homogeneous(false);");
          m_Label2.set_halign(Gtk::Align::START);
          m_Label2.set_valign(Gtk::Align::START);
          m_box1.append(m_Label2);

          pPackBox = Gtk::make_managed<PackBox>(false, 0, false, Gtk::Align::FILL, 10);
          m_box1.append(*pPackBox);

          pPackBox = Gtk::make_managed<PackBox>(false, 0, true, Gtk::Align::FILL, 10);
          m_box1.append(*pPackBox);

          m_box1.append(m_separator2);

          break;
        }

        case 3:
        {
          // This demonstrates the ability to use Gtk::Align::END to
          // right justify widgets.  First, we create a new box as before.
          auto pPackBox = Gtk::make_managed<PackBox>();

          // create the label that will be put at the end.
          m_Label1.set_text("end");

          // pack it using Gtk::Align::END, so it is put on the right side
          // of the PackBox.
          m_Label1.set_halign(Gtk::Align::END);
          m_Label1.set_hexpand(true);
          pPackBox->append(m_Label1);

          m_box1.append(*pPackBox);

          // This explicitly sets the separator to 700 pixels wide by 5 pixels
          // high.  This is so the hbox we created will also be 700 pixels wide,
          // and the "end" label will be separated from the other labels in the
          // hbox.  Otherwise, all the widgets in the hbox would be packed as
          // close together as possible.
          m_separator1.set_size_request(700, 5);

          // pack the separator into the vbox.
          m_box1.append(m_separator1);

          break;
        }

        default:
        {
          std::cerr << "Unexpected command-line option." << std::endl;
          break;
        }
      }

      // Connect the signal to hide the window:
      m_buttonQuit.signal_clicked().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_button_quit_clicked) );

      // pack the button into the quitbox.
      m_boxQuit.append(m_buttonQuit);
      m_buttonQuit.set_hexpand(true);
      m_buttonQuit.set_halign(Gtk::Align::CENTER);
      m_box1.append(m_boxQuit);

      // pack the vbox (box1) which now contains all our widgets, into the
      // main window.
      set_child(m_box1);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit_clicked()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>
    #include <iostream>
    #include <cstdlib>

    #define GTK_APPLICATION_RECEIVES_COMMAND_LINE_ARGUMENTS 0

    #if GTK_APPLICATION_RECEIVES_COMMAND_LINE_ARGUMENTS
    namespace
    {
    int on_command_line(const Glib::RefPtr<Gio::ApplicationCommandLine>& command_line,
                        Glib::RefPtr<Gtk::Application>& app)
    {
      int argc = 0;
      char** argv = command_line->get_arguments(argc);

      for (int i = 0; i < argc; ++i)
        std::cout << "argv[" << i << "] = " << argv[i] << std::endl;

      app->activate(); // Without activate() the window won't be shown.
      return EXIT_SUCCESS;
    }
    } // anonymous namespace
    #endif

    int main(int argc, char *argv[])
    {
      if (argc != 2)
      {
        std::cerr << "Usage: example <num>, where <num> is 1, 2, or 3." << std::endl;
        return EXIT_FAILURE;
      }

      int argc1 = argc;

    #if GTK_APPLICATION_RECEIVES_COMMAND_LINE_ARGUMENTS
      // The Gio::Application::Flags::HANDLES_COMMAND_LINE flag and the
      // on_command_line() signal handler are not necessary. This program is simpler
      // without them, and with argc = 1 in the call to Gtk::Application::make_window_and_run().
      // They are included to show a program with Gio::Application::Flags::HANDLES_COMMAND_LINE.
      // Gio::Application::Flags::NON_UNIQUE makes it possible to run several instances of
      // this application simultaneously.
      auto app = Gtk::Application::create(
        "org.gtkmm.example", Gio::Application::Flags::HANDLES_COMMAND_LINE | Gio::Application::Flags::NON_UNIQUE);

      // Note after = false.
      // Only one signal handler is invoked. This signal handler must run before
      // the default signal handler, or else it won't run at all.
      app->signal_command_line().connect(
        [&app](const auto& command_line)
        { return on_command_line(command_line, app); }, false);
    #else
      // Gio::Application::Flags::NON_UNIQUE makes it possible to run several instances of
      // this application simultaneously.
      argc1 = 1; // Don't give the command line arguments to Gtk::Application.
      auto app = Gtk::Application::create("org.gtkmm.example", Gio::Application::Flags::NON_UNIQUE);
    #endif

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc1, argv, std::atoi(argv[1]));
    }

File: `packbox.cc` (For use with gtkmm 4)

    #include "packbox.h"
    #include <map>

    namespace
    {
      const std::map<Gtk::Align, Glib::ustring> align_string = {
        {Gtk::Align::FILL, "Gtk::Align::FILL"},
        {Gtk::Align::START, "Gtk::Align::START"},
        {Gtk::Align::END, "Gtk::Align::END"},
        {Gtk::Align::CENTER, "Gtk::Align::CENTER"},
        {Gtk::Align::BASELINE, "Gtk::Align::BASELINE"},
      };
    }

    PackBox::PackBox(bool homogeneous, int spacing, bool expand, Gtk::Align align, int margin)
    : Gtk::Box(Gtk::Orientation::HORIZONTAL, spacing)
    {
      set_homogeneous(homogeneous);

      m_buttons[0].set_label("box.append(button);");
      m_buttons[1].set_label("expand=" + Glib::ustring(expand ? "true" : "false"));
      m_buttons[2].set_label(align_string.at(align));
      m_buttons[3].set_label("margin=" + Glib::ustring::format(margin));

      for (auto& button : m_buttons)
      {
        append(button);
        button.set_hexpand(expand);
        button.set_halign(align);
        button.set_margin_start(margin);
        button.set_margin_end(margin);
      }
    }

#### Grade

Uma Grid dinamicamente estabelece widgets filhos em linhas e colunas. As dimensões da grade não precisa ser especificado no construtor.

Child widgets can span multiple rows or columns, using attach(), or added next to an existing widget inside the grid with attach_next_to(). Individual rows and columns of the grid can be set to have uniform height or width with set_row_homogeneous() and set_column_homogeneous().

You can set the margin and expand properties of the child Widgets to control their spacing and their behavior when the Grid is resized.

Reference

##### Exemplo

This example creates a window with three buttons in a grid. The first two buttons are in the upper row, from left to right. A third button is attached underneath the first button, in a new lower row, spanning two columns.

Grade

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    private:
      // Signal handlers:
      void on_button_quit();
      void on_button_numbered(const Glib::ustring& data);

      // Child widgets:
      Gtk::Grid m_grid;
      Gtk::Button m_button_1, m_button_2, m_button_quit;
    };

    #endif /* GTKMM_EXAMPLEWINDOW_H */

File: `examplewindow.cc` (For use with gtkmm 4)

    #include <iostream>
    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_button_1("button 1"),
      m_button_2("button 2"),
      m_button_quit("Quit")
    {
      set_title("Gtk::Grid");

      m_grid.set_margin(12);
      set_child(m_grid);

      m_grid.attach(m_button_1, 0, 0);
      m_grid.attach(m_button_2, 1, 0);
      m_grid.attach_next_to(m_button_quit, m_button_1, Gtk::PositionType::BOTTOM, 2, 1);

      m_button_1.signal_clicked().connect(
        sigc::bind( sigc::mem_fun(*this, &ExampleWindow::on_button_numbered), "button 1") );
      m_button_2.signal_clicked().connect(
        sigc::bind( sigc::mem_fun(*this, &ExampleWindow::on_button_numbered), "button 2") );

      m_button_quit.signal_clicked().connect(sigc::mem_fun(*this,
        &ExampleWindow::on_button_quit) );
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void
    ExampleWindow::on_button_numbered(const Glib::ustring& data)
    {
      std::cout << data << " was pressed" << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Painel com abas

A Notebook has a set of stacked `pages`, each of which contains widgets. Labelled `tabs` allow the user to select the pages. Notebooks allow several sets of widgets to be placed in a small space, by only showing one page at a time. For instance, they are often used in preferences dialogs.

Use the append_page(), prepend_page() and insert_page() methods to add tabbed pages to the `Notebook`, supplying the child widget and the name for the tab.

To discover the currently visible page, use the get_current_page() method. This returns the page number, and then calling get_nth_page() with that number will give you a pointer to the actual child widget.

Para alterar programaticamente a página selecionada, use o método set_current_page().

Reference

##### Exemplo

Painel com abas

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_quit();
      void on_notebook_switch_page(Gtk::Widget* page, guint page_num);

      //Child widgets:
      Gtk::Box m_VBox;
      Gtk::Notebook m_Notebook;
      Gtk::Label m_Label1, m_Label2;

      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include <iostream>
    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Label1("Contents of tab 1"),
      m_Label2("Contents of tab 2"),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::Notebook example");
      set_default_size(400, 200);

      m_VBox.set_margin(10);
      set_child(m_VBox);

      //Add the Notebook, with the button underneath:
      m_Notebook.set_margin(10);
      m_Notebook.set_expand();
      m_VBox.append(m_Notebook);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::CENTER);
      m_Button_Quit.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_quit) );

      //Add the Notebook pages:
      m_Notebook.append_page(m_Label1, "First");
      m_Notebook.append_page(m_Label2, "Second");

      m_Notebook.signal_switch_page().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_notebook_switch_page) );
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void ExampleWindow::on_notebook_switch_page(Gtk::Widget* /* page */, guint page_num)
    {
      std::cout << "Switched to tab with index " << page_num << std::endl;

      //You can also use m_Notebook.get_current_page() to get this index.
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Assistente

Gtk::Assistant is deprecated since gtkmm 4.10. There is no replacement in gtkmm. libadwaita (a C library) has replacement parts (like AdwCarousel). In some cases, a Gtk::Notebook might be an acceptable replacement.

An Assistant splits a complex operation into steps. Each step is a page, containing a header, a child widget and an action area. The Assistant's action area has navigation buttons which update automatically depending on the type of the page, set with set_page_type().

Use os métodos append_page(), prepend_page e insert_page() para adicionar páginas ao Assistant, fornecendo o widget filho para cada página.

To determine the currently-visible page, use the get_current_page() method, and pass the result to get_nth_page(), which returns a pointer to the actual widget. To programmatically change the current page, use the set_current_page() method.

To set the title of a page, use the set_page_title() method.

Para adicionar widgets para a área de ação, usar o método add_action_widget(). Eles serão acondicionados ao lado dos botões padrão. Usar o método remove_action_widget() para remover widgets.

Reference

##### Exemplo

Assistente

Source Code

File: `exampleassistant.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEASSISTANT_H
    #define GTKMM_EXAMPLEASSISTANT_H

    #include <gtkmm.h>

    class ExampleAssistant : public Gtk::Assistant
    {
    public:
      ExampleAssistant();
      virtual ~ExampleAssistant();

      void get_result(bool& check_state, Glib::ustring& entry_text);

    private:
      // Signal handlers:
      void on_assistant_apply();
      void on_assistant_cancel();
      void on_assistant_close();
      void on_assistant_prepare(Gtk::Widget* widget);
      void on_entry_changed();

      // Member functions:
      void print_status();

      // Child widgets:
      Gtk::Box m_box;
      Gtk::Label m_label1, m_label2;
      Gtk::CheckButton m_check;
      Gtk::Entry m_entry;
    };

    #endif /* GTKMM_EXAMPLEASSISTANT_H */

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include "exampleassistant.h"
    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    private:
      // Signal handlers:
      void on_button_clicked();
      void on_assistant_apply();

      // Child widgets:
      Gtk::Grid m_grid;
      Gtk::Button m_button;
      Gtk::Label m_label1, m_label2;
      Gtk::CheckButton m_check;
      Gtk::Entry m_entry;
      ExampleAssistant m_assistant;
    };

    #endif /* GTKMM_EXAMPLEWINDOW_H */

File: `exampleassistant.cc` (For use with gtkmm 4)

    #include <iostream>
    #include "exampleassistant.h"

    ExampleAssistant::ExampleAssistant()
    : m_box(Gtk::Orientation::HORIZONTAL, 12),
      m_label1("Type text to allow the assistant to continue:"),
      m_label2("Confirmation page"),
      m_check("Optional extra information")
    {
      set_title("Gtk::Assistant example");
      set_default_size(400, 200);

      m_box.append(m_label1);
      m_box.append(m_entry);
      m_label1.set_wrap();
      m_label1.set_valign(Gtk::Align::CENTER);
      m_entry.set_valign(Gtk::Align::CENTER);

      append_page(m_box);
      append_page(m_check);
      append_page(m_label2);

      set_page_title(*get_nth_page(0), "Page 1");
      set_page_title(*get_nth_page(1), "Page 2");
      set_page_title(*get_nth_page(2), "Confirmation");

      set_page_complete(m_check, true);
      set_page_complete(m_label2, true);

      set_page_type(m_box, Gtk::AssistantPage::Type::INTRO);
      set_page_type(m_label2, Gtk::AssistantPage::Type::CONFIRM);

      signal_apply().connect(sigc::mem_fun(*this,
        &ExampleAssistant::on_assistant_apply));
      signal_cancel().connect(sigc::mem_fun(*this,
        &ExampleAssistant::on_assistant_cancel));
      signal_close().connect(sigc::mem_fun(*this,
        &ExampleAssistant::on_assistant_close));
      signal_prepare().connect(sigc::mem_fun(*this,
        &ExampleAssistant::on_assistant_prepare));

      m_entry.signal_changed().connect(sigc::mem_fun(*this,
        &ExampleAssistant::on_entry_changed));
    }

    ExampleAssistant::~ExampleAssistant()
    {
    }

    void ExampleAssistant::get_result(bool& check_state, Glib::ustring& entry_text)
    {
      check_state = m_check.get_active();
      entry_text = m_entry.get_text();
    }

    void ExampleAssistant::on_assistant_apply()
    {
      std::cout << "Apply was clicked";
      print_status();
    }

    void ExampleAssistant::on_assistant_cancel()
    {
      std::cout << "Cancel was clicked";
      print_status();
      set_visible(false);
    }

    void ExampleAssistant::on_assistant_close()
    {
      std::cout << "Assistant was closed";
      print_status();
      set_visible(false);
    }

    void ExampleAssistant::on_assistant_prepare(Gtk::Widget* /* widget */)
    {
      set_title(Glib::ustring::compose("Gtk::Assistant example (Page %1 of %2)",
        get_current_page() + 1, get_n_pages()));
    }

    void ExampleAssistant::on_entry_changed()
    {
      // The page is only complete if the entry contains text.
      if(m_entry.get_text_length())
        set_page_complete(m_box, true);
      else
        set_page_complete(m_box, false);
    }

    void ExampleAssistant::print_status()
    {
      std::cout << ", entry contents: \"" << m_entry.get_text()
        << "\", checkbutton status: " << m_check.get_active() << std::endl;
    }

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include "exampleassistant.h"

    ExampleWindow::ExampleWindow()
    : m_button("Show the assistant"),
      m_label1("State of assistant checkbutton:", Gtk::Align::START, Gtk::Align::CENTER),
      m_label2("Contents of assistant entry:", Gtk::Align::START, Gtk::Align::CENTER)
    {
      set_title("Gtk::Assistant example");

      m_grid.set_row_homogeneous(true);
      m_grid.set_column_spacing(5);
      m_grid.set_margin(12);

      m_grid.attach(m_button, 0, 0, 2, 1);
      m_button.set_hexpand(true);
      m_button.set_valign(Gtk::Align::CENTER);

      m_grid.attach(m_label1, 0, 1, 1, 1);

      m_grid.attach(m_label2, 0, 2, 1, 1);

      m_grid.attach(m_check, 1, 1, 1, 1);
      m_check.set_halign(Gtk::Align::START);

      m_grid.attach(m_entry, 1, 2, 1, 1);
      m_entry.set_hexpand(true);

      set_child(m_grid);

      m_button.signal_clicked().connect(sigc::mem_fun(*this,
        &ExampleWindow::on_button_clicked));
      m_assistant.signal_apply().connect(sigc::mem_fun(*this,
        &ExampleWindow::on_assistant_apply));

      m_check.set_sensitive(false);
      m_entry.set_sensitive(false);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_assistant_apply()
    {
      bool check_state;
      Glib::ustring entry_text;

      m_assistant.get_result(check_state, entry_text);
      m_check.set_active(check_state);
      m_entry.set_text(entry_text);
    }

    void ExampleWindow::on_button_clicked()
    {
      m_assistant.set_visible(true);
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Other Multi-item Containers

There are other multi-item containers. See the reference documentation for a complete list. Here are links to some example programs that show containers, which are not mentioned elsewhere in this tutorial.

Source Code, ActionBar

Source Code, FlowBox

## ListView, GridView, ColumnView

Lists are intended to be used whenever developers want to display many objects in roughly the same way. They are perfectly fine to be used for very short lists of only 2 or 3 items, but generally scale fine to thousands of items.

Lists are meant to be used with changing data, both with the items themselves changing as well as the list adding and removing items. Of course, they work just as well with static data.

The List Widget Overview chapter in the GTK documentation contains more information about list widgets.

Some examples are shown in this chapter. There are more examples in the listmodelviews directory in gtkmm-documentation's examples.

### The Data Model

The data model is a class that implements the Gio::ListModel interface. Examples of such classes are Gio::ListStore (not to be confused with the deprecated Gtk::ListStore), Gtk:StringList, Gtk:DirectoryList and Pango::FontMap.

The elements in a model are called items. All items are instances of a subclass of Glib::Object. For instance, you might have a ColumnView with one integer and one text column, like so:

    class ModelColumns : public Glib::Object
    {
    public:
      int m_col_id;
      Glib::ustring m_col_name;

      static Glib::RefPtr<ModelColumns> create(
        int col_id, const Glib::ustring& col_name)
      {
        return Glib::make_refptr_for_instance<ModelColumns>(
          new ModelColumns(col_id, col_name));
      }

    protected:
      ModelColumns(int col_id, const Glib::ustring& col_name)
      : m_col_id(col_id), m_col_name(col_name)
      {}
    };

    Glib::RefPtr<Gio::ListStore<ModelColumns>> m_ListStore;

Every item in a model has a position which is the unsigned integer that describes where in the model the item is located. The first item in a model is at position 0. The position of an item can of course change as other items are added to or removed from the model.

Gio::ListStore Reference

StringList Reference

DirectoryList Reference

### The Selection Model

The selection model is a class that implements the Gtk::SelectionModel interface. You can choose between NoSelection, SingleSelection and MultiSelection.

NoSelection Reference

SingleSelection Reference

MultiSelection Reference

### The Factory

Data from the data model is added to the view by a factory, which is a subclass of ListItemFactory. There is only one such subclass in gtkmm, SignalListItemFactory. Data from the model is added to the view with signal handlers connected to a SignalListItemFactory.

SignalListItemFactory Reference

### Visualização

The View is the widget that displays the model data and allows the user to interact with it. The View can show all of the model's columns, or just some, and it can show them in various ways.

An important requirement for views (especially views of long lists) is that they need to know which items are not visible so they can be recycled. Views achieve that by implementing the Scrollable interface and expecting to be placed directly into a ScrolledWindow.

There are different view widgets to choose from.

#### ListView

The ListView shows a 1-dimensional list with one column.

Reference

##### Exemplo

ListView

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      // Signal handlers:
      void on_button_quit();
      void on_setup_label(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_name(const Glib::RefPtr<Gtk::ListItem>& list_item);

      // Child widgets:
      Gtk::Box m_VBox;
      Gtk::Label m_Heading;
      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::ListView m_ListView;
      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;

      Glib::RefPtr<Gtk::StringList> m_StringList;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Heading("<b>Name</b>", Gtk::Align::START),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::ListView (Gtk::StringList) example");
      set_default_size(300, 200);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      // Add the ListView, inside a ScrolledWindow, with the heading above
      // and the button underneath.
      m_Heading.set_use_markup();
      m_VBox.append(m_Heading);
      m_ScrolledWindow.set_child(m_ListView);

      // Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(5);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_quit));

      // Create the list model:
      m_StringList = Gtk::StringList::create({"Billy Bob", "Joey Jojo", "Rob McRoberts"});

      // Set list model and selection model.
      auto selection_model = Gtk::SingleSelection::create(m_StringList);
      selection_model->set_autoselect(false);
      selection_model->set_can_unselect(true);
      m_ListView.set_model(selection_model);
      m_ListView.add_css_class("data-table"); // high density table

      // Add the factory for the ListView's single column.
      auto factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_setup_label));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_name));
      m_ListView.set_factory(factory);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void ExampleWindow::on_setup_label(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      list_item->set_child(*Gtk::make_managed<Gtk::Label>("", Gtk::Align::START));
    }

    void ExampleWindow::on_bind_name(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto pos = list_item->get_position();
      if (pos == GTK_INVALID_LIST_POSITION)
        return;
      auto label = dynamic_cast<Gtk::Label*>(list_item->get_child());
      if (!label)
        return;
      label->set_text(m_StringList->get_string(pos));
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### GridView

The GridView shows a 2-dimensional grid.

Reference

##### Exemplo

GridView

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>
    #include <gdkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      class ModelColumns;
      // Signal handlers:
      void on_button_quit();
      void on_item_activated(unsigned int position);
      void on_selection_changed();
      void on_setup_listitem(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_listitem(const Glib::RefPtr<Gtk::ListItem>& list_item);
      int on_model_sort(const Glib::RefPtr<const ModelColumns>& a, const Glib::RefPtr<const ModelColumns>& b);

      void add_entry(const std::string& filename, const Glib::ustring& description);

      // A Gio::ListStore stores filename, description and texture.
      class ModelColumns : public Glib::Object
      {
      public:
        std::string m_filename;
        Glib::ustring  m_description;
        Glib::RefPtr<Gdk::Texture> m_texture;

        static Glib::RefPtr<ModelColumns> create(const std::string& filename,
          const Glib::ustring& description, const Glib::RefPtr<Gdk::Texture>& texture)
        {
          return Glib::make_refptr_for_instance<ModelColumns>(
            new ModelColumns(filename, description, texture));
        }

      protected:
        ModelColumns(const std::string& filename, const Glib::ustring& description,
          const Glib::RefPtr<Gdk::Texture>& texture)
        : m_filename(filename), m_description(description), m_texture(texture)
        { }
      }; // ModelColumns

      Glib::RefPtr<Gio::ListStore<ModelColumns>> m_data_model;
      Glib::RefPtr<Gtk::SingleSelection> m_selection_model;
      Glib::RefPtr<Gtk::SignalListItemFactory> m_factory;

      // Child widgets:
      Gtk::Box m_VBox;
      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::GridView m_GridView;
      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <array>
    #include <iostream>

    namespace
    {
      struct GridEntry
      {
        std::string m_filename;
        Glib::ustring m_description;
      };

      std::array<GridEntry, 8> entries =
      {
        GridEntry{"mozilla-firefox.png", "<b>Mozilla Firefox</b> Logo"},
        GridEntry{"xmms.xpm",            "<b>XMMS</b> Logo"},
        GridEntry{"gnome-dice-1.svg",    "<b>Gnome Dice 1</b> Logo"},
        GridEntry{"gnome-dice-2.svg",    "<b>Gnome Dice 2</b> Logo"},
        GridEntry{"gnome-dice-3.svg",    "<b>Gnome Dice 3</b> Logo"},
        GridEntry{"gnome-dice-4.svg",    "<b>Gnome Dice 4</b> Logo"},
        GridEntry{"gnome-dice-5.svg",    "<b>Gnome Dice 5</b> Logo"},
        GridEntry{"gnome-dice-6.svg",    "<b>Gnome Dice 6</b> Logo"}
      };

    } // anonymous namespace

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::GridView (Gio::ListStore) example");
      set_default_size(400, 400);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      // Add the GridView inside a ScrolledWindow, with the button underneath:
      m_ScrolledWindow.set_child(m_GridView);

      // Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(6);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_quit));

      // Create the data model:
      m_data_model = Gio::ListStore<ModelColumns>::create();
      m_selection_model = Gtk::SingleSelection::create(m_data_model);
      m_selection_model->set_autoselect(false);

      m_factory = Gtk::SignalListItemFactory::create();
      m_factory->signal_setup().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_setup_listitem));
      m_factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_listitem));

      // Fill the Gio::ListStore's data model and sort it.
      for (const auto& entry : entries)
        add_entry(entry.m_filename, entry.m_description);
      m_data_model->sort(sigc::mem_fun(*this, &ExampleWindow::on_model_sort));

      m_GridView.set_model(m_selection_model);
      m_GridView.set_factory(m_factory);

      m_GridView.signal_activate().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_item_activated));
      m_selection_model->property_selected().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_selection_changed));
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void ExampleWindow::on_setup_listitem(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      // Each ListItem contains a vertical Box with an Image and a Label.
      auto vBox = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL);
      auto picture = Gtk::make_managed<Gtk::Picture>();
      picture->set_can_shrink(false);
      picture->set_halign(Gtk::Align::CENTER);
      picture->set_valign(Gtk::Align::END);
      vBox->append(*picture);
      vBox->append(*Gtk::make_managed<Gtk::Label>());
      list_item->set_child(*vBox);
    }

    void ExampleWindow::on_bind_listitem(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(list_item->get_item());
      if (!col)
        return;
      auto vBox = dynamic_cast<Gtk::Box*>(list_item->get_child());
      if (!vBox)
        return;
      auto picture = dynamic_cast<Gtk::Picture*>(vBox->get_first_child());
      if (!picture)
        return;
      auto label = dynamic_cast<Gtk::Label*>(picture->get_next_sibling());
      if (!label)
        return;
      picture->set_paintable(col->m_texture);
      label->set_markup(col->m_description);
    }

    void ExampleWindow::on_item_activated(unsigned int position)
    {
      auto col = m_data_model->get_item(position);
      if (!col)
        return;

      const std::string filename = col->m_filename;
      const Glib::ustring description = col->m_description;

      std::cout  << "Item activated: filename=" << filename
        << ", description=" << description << std::endl;
    }

    void ExampleWindow::on_selection_changed()
    {
      auto position = m_selection_model->get_selected();
      auto col = m_data_model->get_item(position);
      if (!col)
        return;

      const std::string filename = col->m_filename;
      const Glib::ustring description = col->m_description;

      std::cout  << "Selection Changed to: filename=" << filename
        << ", description=" << description << std::endl;
    }

    int ExampleWindow::on_model_sort(const Glib::RefPtr<const ModelColumns>& a,
      const Glib::RefPtr<const ModelColumns>& b)
    {
      return (a->m_description < b->m_description) ? -1 : ((a->m_description > b->m_description) ? 1 : 0);
    }

    void ExampleWindow::add_entry(const std::string& filename,
            const Glib::ustring& description )
    {
      try
      {
         auto pixbuf = Gdk::Pixbuf::create_from_file(filename);
         auto texture = Gdk::Texture::create_for_pixbuf(pixbuf);
         m_data_model->append(ModelColumns::create(filename, description, texture));
      }
      catch (const Gdk::PixbufError& ex)
      {
        std::cerr << "Gdk::PixbufError: " << ex.what() << std::endl;
      }
      catch (const Glib::FileError& ex)
      {
        std::cerr << "Glib::FileError: " << ex.what() << std::endl;
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### ColumnView

The ColumnView shows a 1-dimensional list with one or more columns.

Reference

##### Exemplo

ColumnView

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      // Signal handlers:
      void on_button_quit();
      void on_setup_label(const Glib::RefPtr<Gtk::ListItem>& list_item, Gtk::Align halign);
      void on_setup_progressbar(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_id(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_name(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_number(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_percentage(const Glib::RefPtr<Gtk::ListItem>& list_item);

      // A Gio::ListStore item.
      class ModelColumns : public Glib::Object
      {
      public:
        unsigned int m_col_id;
        Glib::ustring m_col_name;
        short m_col_number;
        int m_col_percentage;

        static Glib::RefPtr<ModelColumns> create(unsigned int col_id,
          const Glib::ustring& col_name, short col_number, int col_percentage)
        {
          return Glib::make_refptr_for_instance<ModelColumns>(
            new ModelColumns(col_id, col_name, col_number, col_percentage));
        }

      protected:
        ModelColumns(unsigned int col_id, const Glib::ustring& col_name,
          short col_number, int col_percentage)
        : m_col_id(col_id), m_col_name(col_name), m_col_number(col_number),
          m_col_percentage(col_percentage)
        {}
      }; // ModelColumns

      // Child widgets:
      Gtk::Box m_VBox;
      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::ColumnView m_ColumnView;
      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;

      Glib::RefPtr<Gio::ListStore<ModelColumns>> m_ListStore;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::ColumnView (Gio::ListStore) example");
      set_default_size(500, 250);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      // Add the ColumnView, inside a ScrolledWindow, with the button underneath:
      m_ScrolledWindow.set_child(m_ColumnView);

      // Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(5);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_quit));

      // Create the List model:
      m_ListStore = Gio::ListStore<ModelColumns>::create();
      m_ListStore->append(ModelColumns::create(1, "Billy Bob", 10, 15));
      m_ListStore->append(ModelColumns::create(2, "Joey Jojo", 20, 40));
      m_ListStore->append(ModelColumns::create(3, "Rob McRoberts", 30, 70));

      // Set list model and selection model.
      auto selection_model = Gtk::SingleSelection::create(m_ListStore);
      selection_model->set_autoselect(false);
      selection_model->set_can_unselect(true);
      m_ColumnView.set_model(selection_model);
      m_ColumnView.add_css_class("data-table"); // high density table

      // Make the columns reorderable.
      // This is not necessary, but it's nice to show the feature.
      m_ColumnView.set_reorderable(true);

      // Add the ColumnView's columns:

      // Id column
      auto factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(sigc::bind(sigc::mem_fun(*this,
        &ExampleWindow::on_setup_label), Gtk::Align::END));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_id));
      auto column = Gtk::ColumnViewColumn::create("ID", factory);
      m_ColumnView.append_column(column);

      // Name column
      factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(sigc::bind(sigc::mem_fun(*this,
        &ExampleWindow::on_setup_label), Gtk::Align::START));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_name));
      column = Gtk::ColumnViewColumn::create("Name", factory);
      m_ColumnView.append_column(column);

      // Number column
      factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(sigc::bind(sigc::mem_fun(*this,
        &ExampleWindow::on_setup_label), Gtk::Align::END));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_number));
      column = Gtk::ColumnViewColumn::create("Formatted number", factory);
      m_ColumnView.append_column(column);

      // Percentage column
      factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_setup_progressbar));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_percentage));
      column = Gtk::ColumnViewColumn::create("Some percentage", factory);
      m_ColumnView.append_column(column);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void ExampleWindow::on_setup_label(
      const Glib::RefPtr<Gtk::ListItem>& list_item, Gtk::Align halign)
    {
      list_item->set_child(*Gtk::make_managed<Gtk::Label>("", halign));
    }

    void ExampleWindow::on_setup_progressbar(
      const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto progressbar = Gtk::make_managed<Gtk::ProgressBar>();
      progressbar->set_show_text(true);
      list_item->set_child(*progressbar);
    }

    void ExampleWindow::on_bind_id(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(list_item->get_item());
      if (!col)
        return;
      auto label = dynamic_cast<Gtk::Label*>(list_item->get_child());
      if (!label)
        return;
      label->set_text(Glib::ustring::format(col->m_col_id));
    }

    void ExampleWindow::on_bind_name(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(list_item->get_item());
      if (!col)
        return;
      auto label = dynamic_cast<Gtk::Label*>(list_item->get_child());
      if (!label)
        return;
      label->set_text(col->m_col_name);
    }

    void ExampleWindow::on_bind_number(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(list_item->get_item());
      if (!col)
        return;
      auto label = dynamic_cast<Gtk::Label*>(list_item->get_child());
      if (!label)
        return;
      // 10 digits, using leading zeroes.
      label->set_text(Glib::ustring::sprintf("%010d", col->m_col_number));
    }

    void ExampleWindow::on_bind_percentage(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(list_item->get_item());
      if (!col)
        return;
      auto progressbar = dynamic_cast<Gtk::ProgressBar*>(list_item->get_child());
      if (!progressbar)
        return;
      progressbar->set_fraction(col->m_col_percentage * 0.01);
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Classificando

The list can be sorted by wrapping it in a SortListModel. There are two ways to do this.

- In a ColumnView, get the ColumnViewSorter from the ColumnView and set it to the SortListModel. Set a Sorter to each ColumnViewColumn. Then the user of your app can sort the items by clicking on a column heading.

- In any view, set a Sorter such as a StringSorter or a NumericSorter to the SortListModel.

SortListModel Reference

StringSorter Reference

NumericSorter Reference

#### Exemplo

SortListModel

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      // Signal handlers:
      void on_button_nosort();
      void on_button_sortheadings();
      void on_button_sortlength();
      void on_button_quit();
      void on_setup_label(const Glib::RefPtr<Gtk::ListItem>& list_item, Gtk::Align halign);
      void on_bind_id(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_name(const Glib::RefPtr<Gtk::ListItem>& list_item);

      // A Gio::ListStore item.
      class ModelColumns : public Glib::Object
      {
      public:
        unsigned int m_col_id;
        Glib::ustring m_col_name;

        static Glib::RefPtr<ModelColumns> create(int col_id, const Glib::ustring& col_name)
        {
          return Glib::make_refptr_for_instance<ModelColumns>(
            new ModelColumns(col_id, col_name));
        }

      protected:
        ModelColumns(int col_id, const Glib::ustring& col_name)
        : m_col_id(col_id), m_col_name(col_name)
        {}
      }; // ModelColumns

      // Child widgets:
      Gtk::Box m_VBox;
      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::ColumnView m_ColumnView;
      Gtk::Box m_ButtonBox;
      Gtk::ToggleButton m_Button_NoSort;
      Gtk::ToggleButton m_Button_SortHeadings;
      Gtk::ToggleButton m_Button_SortLength;
      Gtk::Button m_Button_Quit;

      Glib::RefPtr<Gtk::SingleSelection> m_SelectionModel;
      Glib::RefPtr<Gio::ListStore<ModelColumns>> m_ListStore;
      Glib::RefPtr<Gtk::SortListModel> m_SortListModel;
      Glib::RefPtr<Gtk::ColumnViewColumn> m_IdColumn;
      Glib::RefPtr<Gtk::ColumnViewColumn> m_NameColumn;
      Glib::RefPtr<Gtk::NumericSorter<Glib::ustring::size_type>> m_LengthSorter;
      Glib::RefPtr<Gtk::NumericSorter<unsigned int>> m_IdSorter;
      Glib::RefPtr<Gtk::StringSorter> m_NameSorter;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_NoSort("Don't Sort"),
      m_Button_SortHeadings("Sort Headings"),
      m_Button_SortLength("Sort Length"),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::ColumnView (Gtk::SortListModel) example");
      set_default_size(400, 350);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      // Add the ColumnView, inside a ScrolledWindow, with the buttons underneath:
      m_ScrolledWindow.set_child(m_ColumnView);

      // Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.set_margin(5);
      m_ButtonBox.set_spacing(10);
      m_ButtonBox.append(m_Button_NoSort);
      m_ButtonBox.append(m_Button_SortHeadings);
      m_ButtonBox.append(m_Button_SortLength);
      m_ButtonBox.append(m_Button_Quit);
      m_Button_NoSort.signal_toggled().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_nosort));
      m_Button_SortHeadings.signal_toggled().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_sortheadings));
      m_Button_SortLength.signal_toggled().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_sortlength));
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_quit));

      // Gtk::CheckButton and Gtk::ToggleButton have set_group() methods.
      // They act as radio buttons, if they are included in a group.
      m_Button_SortHeadings.set_group(m_Button_NoSort);
      m_Button_SortLength.set_group(m_Button_NoSort);

      // Create the List model.
      m_ListStore = Gio::ListStore<ModelColumns>::create();
      m_ListStore->append(ModelColumns::create(1, "Billy Bob"));
      m_ListStore->append(ModelColumns::create(11, "Billy Bob Junior"));
      m_ListStore->append(ModelColumns::create(12, "Sue Bob"));
      m_ListStore->append(ModelColumns::create(2, "Joey Jojo"));
      m_ListStore->append(ModelColumns::create(3, "Rob McRoberts"));
      m_ListStore->append(ModelColumns::create(31, "Xavier McRoberts"));

      // Create the sort model.
      auto size_expression = Gtk::ClosureExpression<Glib::ustring::size_type>::create(
        [](const Glib::RefPtr<Glib::ObjectBase>& item)->Glib::ustring::size_type
        {
          const auto col = std::dynamic_pointer_cast<ModelColumns>(item);
          return col ? col->m_col_name.size() : 0;
        });
      m_LengthSorter = Gtk::NumericSorter<Glib::ustring::size_type>::create(size_expression);
      m_LengthSorter->set_sort_order(Gtk::SortType::ASCENDING);
      m_SortListModel = Gtk::SortListModel::create(m_ListStore, m_LengthSorter);

      // Set list model and selection model.
      m_SelectionModel = Gtk::SingleSelection::create(m_ListStore);
      m_SelectionModel->set_autoselect(false);
      m_SelectionModel->set_can_unselect(true);
      m_ColumnView.set_model(m_SelectionModel);
      m_ColumnView.add_css_class("data-table"); // high density table

      // Make the columns reorderable.
      // This is not necessary, but it's nice to show the feature.
      m_ColumnView.set_reorderable(true);

      // Add the ColumnView's columns:

      // Id column
      auto factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(sigc::bind(sigc::mem_fun(*this,
        &ExampleWindow::on_setup_label), Gtk::Align::END));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_id));
      m_IdColumn = Gtk::ColumnViewColumn::create("ID", factory);
      m_ColumnView.append_column(m_IdColumn);
      auto uint_expression = Gtk::ClosureExpression<unsigned int>::create(
        [](const Glib::RefPtr<Glib::ObjectBase>& item)->unsigned int
        {
          const auto col = std::dynamic_pointer_cast<ModelColumns>(item);
          return col ? col->m_col_id : 0;
        });
      m_IdSorter = Gtk::NumericSorter<unsigned int>::create(uint_expression);

      // Name column
      factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(sigc::bind(sigc::mem_fun(*this,
        &ExampleWindow::on_setup_label), Gtk::Align::START));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_name));
      m_NameColumn = Gtk::ColumnViewColumn::create("Name", factory);
      m_ColumnView.append_column(m_NameColumn);
      auto ustring_expression = Gtk::ClosureExpression<Glib::ustring>::create(
        [](const Glib::RefPtr<Glib::ObjectBase>& item)->Glib::ustring
        {
          const auto col = std::dynamic_pointer_cast<ModelColumns>(item);
          return col ? col->m_col_name : "";
        });
      m_NameSorter = Gtk::StringSorter::create(ustring_expression);

      // Show the list model without sorting.
      m_Button_NoSort.set_active(true);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_nosort()
    {
      if (m_Button_NoSort.get_active())
      {
        m_SelectionModel->set_model(m_ListStore);
        m_IdColumn->set_sorter({});
        m_NameColumn->set_sorter({});
      }
    }

    void ExampleWindow::on_button_sortheadings()
    {
      if (m_Button_SortHeadings.get_active())
      {
        m_SortListModel->set_sorter(m_ColumnView.get_sorter());
        m_SelectionModel->set_model(m_SortListModel);
        m_IdColumn->set_sorter(m_IdSorter);
        m_NameColumn->set_sorter(m_NameSorter);
      }
    }

    void ExampleWindow::on_button_sortlength()
    {
      if (m_Button_SortLength.get_active())
      {
        m_SortListModel->set_sorter(m_LengthSorter);
        m_SelectionModel->set_model(m_SortListModel);
        m_IdColumn->set_sorter({});
        m_NameColumn->set_sorter({});
      }
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void ExampleWindow::on_setup_label(
      const Glib::RefPtr<Gtk::ListItem>& list_item, Gtk::Align halign)
    {
      list_item->set_child(*Gtk::make_managed<Gtk::Label>("", halign));
    }

    void ExampleWindow::on_bind_id(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(list_item->get_item());
      if (!col)
        return;
      auto label = dynamic_cast<Gtk::Label*>(list_item->get_child());
      if (!label)
        return;
      label->set_text(Glib::ustring::format(col->m_col_id));
    }

    void ExampleWindow::on_bind_name(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(list_item->get_item());
      if (!col)
        return;
      auto label = dynamic_cast<Gtk::Label*>(list_item->get_child());
      if (!label)
        return;
      label->set_text(col->m_col_name);
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Filtering

The list can be filtered by wrapping it in a FilterListModel. Set a Filter such as a StringFilter or a BoolFilter to the FilterListModel.

FilterListModel Reference

StringFilter Reference

BoolFilter Reference

#### Exemplo

FilterListModel

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      // Signal handlers:
      void on_button_showall();
      void on_button_showj();
      void on_button_showm();
      void on_button_quit();
      void on_setup_label(const Glib::RefPtr<Gtk::ListItem>& list_item, Gtk::Align halign);
      void on_bind_id(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_name(const Glib::RefPtr<Gtk::ListItem>& list_item);

      // A Gio::ListStore item.
      class ModelColumns : public Glib::Object
      {
      public:
        unsigned int m_col_id;
        Glib::ustring m_col_name;

        static Glib::RefPtr<ModelColumns> create(int col_id, const Glib::ustring& col_name)
        {
          return Glib::make_refptr_for_instance<ModelColumns>(
            new ModelColumns(col_id, col_name));
        }

      protected:
        ModelColumns(int col_id, const Glib::ustring& col_name)
        : m_col_id(col_id), m_col_name(col_name)
        {}
      }; // ModelColumns

      // Child widgets:
      Gtk::Box m_VBox;
      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::ColumnView m_ColumnView;
      Gtk::Box m_ButtonBox;
      Gtk::ToggleButton m_Button_ShowAll;
      Gtk::ToggleButton m_Button_ShowJ;
      Gtk::ToggleButton m_Button_ShowM;
      Gtk::Button m_Button_Quit;

      Glib::RefPtr<Gtk::SingleSelection> m_SelectionModel;
      Glib::RefPtr<Gio::ListStore<ModelColumns>> m_ListStore;
      Glib::RefPtr<Gtk::FilterListModel> m_FilterListModel;
      Glib::RefPtr<Gtk::StringFilter> m_StringFilter;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_ShowAll("Show All"),
      m_Button_ShowJ("Show J"),
      m_Button_ShowM("Show M"),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::ColumnView (Gtk::FilterListModel) example");
      set_default_size(400, 350);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      // Add the ColumnView, inside a ScrolledWindow, with the buttons underneath:
      m_ScrolledWindow.set_child(m_ColumnView);

      // Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.set_margin(5);
      m_ButtonBox.set_spacing(10);
      m_ButtonBox.append(m_Button_ShowAll);
      m_ButtonBox.append(m_Button_ShowJ);
      m_ButtonBox.append(m_Button_ShowM);
      m_ButtonBox.append(m_Button_Quit);
      m_Button_ShowAll.signal_toggled().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_showall));
      m_Button_ShowJ.signal_toggled().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_showj));
      m_Button_ShowM.signal_toggled().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_showm));
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_quit));

      // Gtk::CheckButton and Gtk::ToggleButton have set_group() methods.
      // They act as radio buttons, if they are included in a group.
      m_Button_ShowJ.set_group(m_Button_ShowAll);
      m_Button_ShowM.set_group(m_Button_ShowAll);

      // Create the List model.
      m_ListStore = Gio::ListStore<ModelColumns>::create();
      m_ListStore->append(ModelColumns::create(1, "Billy Bob"));
      m_ListStore->append(ModelColumns::create(11, "Billy Bob Junior"));
      m_ListStore->append(ModelColumns::create(12, "Sue Bob"));
      m_ListStore->append(ModelColumns::create(2, "Joey Jojo"));
      m_ListStore->append(ModelColumns::create(3, "Rob McRoberts"));
      m_ListStore->append(ModelColumns::create(31, "Xavier McRoberts"));

      // Create the filter model.
      auto expression = Gtk::ClosureExpression<Glib::ustring>::create(
        [](const Glib::RefPtr<Glib::ObjectBase>& item)->Glib::ustring
        {
          const auto col = std::dynamic_pointer_cast<ModelColumns>(item);
          return col ? col->m_col_name : "";
        });
      m_StringFilter = Gtk::StringFilter::create(expression);
      m_StringFilter->set_ignore_case(false);
      m_StringFilter->set_match_mode(Gtk::StringFilter::MatchMode::SUBSTRING);
      m_FilterListModel = Gtk::FilterListModel::create(m_ListStore, m_StringFilter);

      // Set list model and selection model.
      m_SelectionModel = Gtk::SingleSelection::create(m_ListStore);
      m_SelectionModel->set_autoselect(false);
      m_SelectionModel->set_can_unselect(true);
      m_ColumnView.set_model(m_SelectionModel);
      m_ColumnView.add_css_class("data-table"); // high density table

      // Make the columns reorderable.
      // This is not necessary, but it's nice to show the feature.
      m_ColumnView.set_reorderable(true);

      // Add the ColumnView's columns:

      // Id column
      auto factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(sigc::bind(sigc::mem_fun(*this,
        &ExampleWindow::on_setup_label), Gtk::Align::END));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_id));
      auto column = Gtk::ColumnViewColumn::create("ID", factory);
      m_ColumnView.append_column(column);

      // Name column
      factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(sigc::bind(sigc::mem_fun(*this,
        &ExampleWindow::on_setup_label), Gtk::Align::START));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_name));
      column = Gtk::ColumnViewColumn::create("Name", factory);
      m_ColumnView.append_column(column);

      // Show the list model without filtering.
      m_Button_ShowAll.set_active(true);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_showall()
    {
      if (m_Button_ShowAll.get_active())
        m_SelectionModel->set_model(m_ListStore);
    }

    void ExampleWindow::on_button_showj()
    {
      if (m_Button_ShowJ.get_active())
      {
       m_StringFilter->set_search("J");
        m_SelectionModel->set_model(m_FilterListModel);
      }
    }

    void ExampleWindow::on_button_showm()
    {
      if (m_Button_ShowM.get_active())
      {
       m_StringFilter->set_search("M");
        m_SelectionModel->set_model(m_FilterListModel);
      }
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void ExampleWindow::on_setup_label(
      const Glib::RefPtr<Gtk::ListItem>& list_item, Gtk::Align halign)
    {
      list_item->set_child(*Gtk::make_managed<Gtk::Label>("", halign));
    }

    void ExampleWindow::on_bind_id(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(list_item->get_item());
      if (!col)
        return;
      auto label = dynamic_cast<Gtk::Label*>(list_item->get_child());
      if (!label)
        return;
      label->set_text(Glib::ustring::format(col->m_col_id));
    }

    void ExampleWindow::on_bind_name(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(list_item->get_item());
      if (!col)
        return;
      auto label = dynamic_cast<Gtk::Label*>(list_item->get_child());
      if (!label)
        return;
      label->set_text(col->m_col_name);
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Displaying Trees

While the deprecated TreeView provided built-in support for trees, the list widgets, and in particular Gio::ListModel, do not. However, gtkmm provides functionality to make trees look and behave like lists for the people who still want to display lists. This is achieved by using the TreeListModel to flatten a tree into a list. The TreeExpander widget can then be used inside a listitem to allow users to expand and collapse rows.

TreeListModel Reference

TreeExpander Reference

#### Exemplo

TreeListModel

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      // Signal handlers:
      void on_button_quit();
      void on_setup_id(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_setup_name(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_id(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_name(const Glib::RefPtr<Gtk::ListItem>& list_item);

      Glib::RefPtr<Gio::ListModel> create_model(
        const Glib::RefPtr<Glib::ObjectBase>& item = {});

      // A Gio::ListStore item.
      class ModelColumns : public Glib::Object
      {
      public:
        int m_col_id;
        Glib::ustring m_col_name;

        static Glib::RefPtr<ModelColumns> create(int col_id, const Glib::ustring& col_name)
        {
          return Glib::make_refptr_for_instance<ModelColumns>(
            new ModelColumns(col_id, col_name));
        }

      protected:
        ModelColumns(int col_id, const Glib::ustring& col_name)
        : m_col_id(col_id), m_col_name(col_name)
        {}
      }; // ModelColumns

      // Child widgets:
      Gtk::Box m_VBox;
      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::ColumnView m_ColumnView;
      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;

      Glib::RefPtr<Gtk::TreeListModel> m_TreeListModel;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::ColumnView (Gtk::TreeListModel) example");
      set_default_size(300, 350);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      // Add the ColumnView, inside a ScrolledWindow, with the button underneath:
      m_ScrolledWindow.set_child(m_ColumnView);

      // Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(5);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_quit));

      // Create the root model:
      auto root = create_model();

      // Set list model and selection model.
      // passthrough must be false when Gtk::TreeExpander is used in the view.
      m_TreeListModel = Gtk::TreeListModel::create(root,
        sigc::mem_fun(*this, &ExampleWindow::create_model),
        /* passthrough */ false, /* autoexpand */ false);
      auto selection_model = Gtk::MultiSelection::create(m_TreeListModel);
      m_ColumnView.set_model(selection_model);
      m_ColumnView.add_css_class("data-table"); // high density table

      // Make the columns reorderable.
      // This is not necessary, but it's nice to show the feature.
      m_ColumnView.set_reorderable(true);

      // Add the ColumnView's columns:

      // Id column
      auto factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_setup_id));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_id));
      auto column = Gtk::ColumnViewColumn::create("ID", factory);
      m_ColumnView.append_column(column);

      // Name column
      factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_setup_name));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_name));
      column = Gtk::ColumnViewColumn::create("Name", factory);
      m_ColumnView.append_column(column);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    Glib::RefPtr<Gio::ListModel> ExampleWindow::create_model(
      const Glib::RefPtr<Glib::ObjectBase>& item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(item);
      auto result = Gio::ListStore<ModelColumns>::create();
      if (!col)
      {
        // Top names
        result->append(ModelColumns::create(1, "Billy Bob"));
        result->append(ModelColumns::create(2, "Joey Jojo"));
        result->append(ModelColumns::create(3, "Rob McRoberts"));
      }
      else
      {
        switch (col->m_col_id)
        {
        case 1:
          result->append(ModelColumns::create(11, "Billy Bob Junior"));
          result->append(ModelColumns::create(12, "Sue Bob"));
          break;
        case 3:
          result->append(ModelColumns::create(31, "Xavier McRoberts"));
          break;
        }
      }

      // If result is empty, it's a leaf in the tree, i.e. an item without children.
      // Returning an empty RefPtr (not a RefPtr with an empty Gio::ListModel)
      // signals that the item is not expandable.
      return (result->get_n_items() > 0) ? result : Glib::RefPtr<Gio::ListModel>();
    }

    void ExampleWindow::on_setup_id(
      const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      // Each ListItem contains a TreeExpander, which contains a Label.
      // The Label shows the ModelColumns::m_col_id. That's done in on_bind_id().
      auto expander = Gtk::make_managed<Gtk::TreeExpander>();
      auto label = Gtk::make_managed<Gtk::Label>();
      label->set_halign(Gtk::Align::END);
      expander->set_child(*label);
      list_item->set_child(*expander);
    }

    void ExampleWindow::on_setup_name(
      const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      list_item->set_child(*Gtk::make_managed<Gtk::Label>("", Gtk::Align::START));
    }

    void ExampleWindow::on_bind_id(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      // When TreeListModel::property_passthrough() is false, ListItem::get_item()
      // is a TreeListRow. TreeExpander needs the TreeListRow.
      // The ModelColumns item is returned by TreeListRow::get_item().
      auto row = std::dynamic_pointer_cast<Gtk::TreeListRow>(list_item->get_item());
      if (!row)
        return;
      auto col = std::dynamic_pointer_cast<ModelColumns>(row->get_item());
      if (!col)
        return;
      auto expander = dynamic_cast<Gtk::TreeExpander*>(list_item->get_child());
      if (!expander)
        return;
      expander->set_list_row(row);
      auto label = dynamic_cast<Gtk::Label*>(expander->get_child());
      if (!label)
        return;
      label->set_text(Glib::ustring::format(col->m_col_id));
    }

    void ExampleWindow::on_bind_name(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto row = std::dynamic_pointer_cast<Gtk::TreeListRow>(list_item->get_item());
      if (!row)
        return;
      auto col = std::dynamic_pointer_cast<ModelColumns>(row->get_item());
      if (!col)
        return;
      auto label = dynamic_cast<Gtk::Label*>(list_item->get_child());
      if (!label)
        return;
      label->set_text(col->m_col_name);
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

## Widget de visualização em árvore

Gtk::TreeView is deprecated since gtkmm 4.10. In new code, use Gtk::ListView for lists and Gtk::ColumnView for tabular lists.

O widget Gtk::TreeView pode conter listas ou árvores de dados, em colunas.

### Modelo

Each Gtk::TreeView has an associated Gtk::TreeModel, which contains the data displayed by the TreeView. Each Gtk::TreeModel can be used by more than one Gtk::TreeView. For instance, this allows the same underlying data to be displayed and edited in 2 different ways at the same time. Or the 2 Views might display different columns from the same Model data, in the same way that 2 SQL queries (or "views") might show different fields from the same database table.

Embora você pode, teoricamente, implementar seu próprio modelo, normalmente você vai usar a classe modelo ListStore ou TreeStore.

Reference

#### ListStore, for rows

The ListStore contains simple rows of data, and each row has no children.

TreeView - ListStore

Reference

#### TreeStore, por hierarquia

The TreeStore contains rows of data, and each row may have child rows.

TreeView - TreeStore

Reference

#### Modelo de colunas

The TreeModelColumnRecord class is used to keep track of the columns and their data types. You add TreeModelColumn instances to the ColumnRecord and then use those TreeModelColumns when getting and setting the data in model rows. You will probably find it convenient to derive a new TreeModelColumnRecord which has your TreeModelColumn instances as member data.

    class ModelColumns : public Gtk::TreeModelColumnRecord
    {
    public:

      ModelColumns()
        { add(m_col_text); add(m_col_number); }

      Gtk::TreeModelColumn<Glib::ustring> m_col_text;
      Gtk::TreeModelColumn<int> m_col_number;
    };

    ModelColumns m_Columns;

You specify the ColumnRecord when creating the Model, like so:

    Glib::RefPtr<Gtk::ListStore> refListStore =
        Gtk::ListStore::create(m_Columns);

As a TreeModelColumnRecord describes structure, not data, it can be shared among multiple models, and this is preferable for efficiency. However, the instance (such as `m_Columns` here) should usually not be static, because it often needs to be instantiated after glibmm has been initialized. The best solution is to make it a lazily instantiated singleton, so that it will be constructed on-demand, whenever the first model accesses it.

#### Adicionando linhas

Add rows to the model with the append(), prepend(), or insert() methods.

    auto iter = m_refListStore->append();

You can dereference the iterator to get the Row:

    auto row = *iter;

##### Adicionando linhas filhas

Gtk::TreeStore models can have child items. Add them with the append(), prepend(), or insert() methods, like so:

    auto iter_child =
        m_refTreeStore->append(row.children());

#### Ajustando valores

You can use the operator[] overload to set the data for a particular column in the row, specifying the TreeModelColumn used to create the model.

    row[m_Columns.m_col_text] = "sometext";

#### Obtenção de valores

You can use the operator[] overload to get the data in a particular column in a row, specifying the TreeModelColumn used to create the model.

    auto strText = row[m_Columns.m_col_text];
    auto number = row[m_Columns.m_col_number];

The compiler will complain if you use an inappropriate type. For instance, this would generate a compiler error:

    //compiler error - no conversion from ustring to int.
    int number = row[m_Columns.m_col_text];

#### "Ocultando" colunas

You might want to associate extra data with each row. If so, just add it as a Model column, but don't add it to the View.

### Visualização

The View is the actual widget (Gtk::TreeView) that displays the model (Gtk::TreeModel) data and allows the user to interact with it. The View can show all of the model's columns, or just some, and it can show them in various ways.

Reference

#### Utilizando um modelo

You can specify a Gtk::TreeModel when constructing the Gtk::TreeView, or you can use the set_model() method, like so:

    m_TreeView.set_model(m_refListStore);

#### Adicionando visualização em colunas

You can use the append_column() method to tell the View that it should display certain Model columns, in a certain order, with a certain column title.

    m_TreeView.append_column("Messages", m_Columns.m_col_text);

When using this simple append_column() overload, the TreeView will display the model data with an appropriate CellRenderer. For instance, strings and numbers are shown in a simple Gtk::Entry widget, and booleans are shown in a Gtk::CheckButton. This is usually what you need. For other column types you must either connect a callback that converts your type into a string representation, with TreeViewColumn::set_cell_data_func(), or derive a custom CellRenderer. Note that (unsigned) short is not supported by default - You could use (unsigned) int or (unsigned) long as the column type instead.

#### More than one Model Column per View Column

To render more than one model column in a view column, you need to create the TreeView::Column widget manually, and use pack_start() to add the model columns to it.

Then use append_column() to add the view Column to the View. Notice that Gtk::TreeView::append_column() is overloaded to accept either a prebuilt Gtk::TreeView::Column widget, or just the TreeModelColumn from which it generates an appropriate Gtk::TreeView::Column widget.

Here is some example code, which has a pixbuf icon and a text name in the same column:

    auto pColumn = Gtk::make_managed<Gtk::TreeView::Column>("Icon Name");

    // m_columns.icon and m_columns.iconname are columns in the model.
    // pColumn is the column in the TreeView:
    pColumn->pack_start(m_columns.icon, /* expand= */ false);
    pColumn->pack_start(m_columns.iconname);

    m_TreeView.append_column(*pColumn);

#### Especificando detalhes do renderizador de célula

The default CellRenderers and their default behavior will normally suffice, but you might occasionally need finer control. For instance, this example code from `gtkmm/demos/gtk-demo/example_treeview_treestore.cc`, appends a Gtk::CellRenderer widget and instructs it to render the data from various model columns through various aspects of its appearance.

    auto cols_count = m_TreeView.append_column_editable("Alex", m_columns.alex);
    auto pColumn = m_TreeView.get_column(cols_count-1);
    if(pColumn)
    {
      auto pRenderer = static_cast<Gtk::CellRendererToggle*>(pColumn->get_first_cell());
      pColumn->add_attribute(pRenderer->property_visible(), m_columns.visible);
      pColumn->add_attribute(pRenderer->property_activatable(), m_columns.world);

You can also connect to CellRenderer signals to detect user actions. For instance:

    auto pRenderer = Gtk::make_managed<Gtk::CellRendererToggle>();
    pRenderer->signal_toggled().connect(
        sigc::bind( sigc::mem_fun(*this,
            &Example_TreeView_TreeStore::on_cell_toggled), m_columns.dave)
    );

#### Células editáveis

##### Automatically-stored editable cells

Cells in a TreeView can be edited in-place by the user. To allow this, use the Gtk::TreeView insert_column_editable() and append_column_editable() methods instead of insert_column() and append_column(). When these cells are edited the new values will be stored immediately in the Model. Note that these methods are templates which can only be instantiated for simple column types such as Glib::ustring, int, and long.

##### Implementing custom logic for editable cells

However, you might not want the new values to be stored immediately. For instance, maybe you want to restrict the input to certain characters or ranges of values.

To achieve this, you should use the normal Gtk::TreeView insert_column() and append_column() methods, then use get_column_cell_renderer() to get the Gtk::CellRenderer used by that column.

You should then cast that Gtk::CellRenderer* to the specific CellRenderer that you expect, so you can use specific API.

For instance, for a CellRendererText, you would set the cell's editable property to true, like so:

    cell->property_editable() = true;

For a CellRendererToggle, you would set the activatable property instead.

You can then connect to the appropriate "edited" signal. For instance, connect to Gtk::CellRendererText::signal_edited(), or Gtk::CellRendererToggle::signal_toggled(). If the column contains more than one CellRenderer then you will need to use Gtk::TreeView::get_column() and then call get_cells() on that view Column.

In your signal handler, you should examine the new value and then store it in the Model if that is appropriate for your application.

### Iterating over Model Rows

Gtk::TreeModel provides a C++ Standard Library-style container of its children, via the children() method. You can use the familiar begin() and end() methods iterator incrementing, like so:

    auto children = refModel->children();
    for (auto iter = children.begin(), end = children.end(); iter != end; ++iter)
    {
      auto row = *iter;
      //Do something with the row - see above for set/get.
    }

If you always want to iterate across the entire range, much more succinct syntax is possible using C++'s range-based `for` loop:

    for (auto row: refModel->children())
    {
      //Do something with the row - see above for set/get.
    }

#### Linhas filhas

When using a Gtk::TreeStore, the rows can have child rows, which can have their own children in turn. Use Gtk::TreeModel::Row::children() to get the container of child Rows:

    Gtk::TreeModel::Children children = row.children();

### Seleção

To find out what rows the user has selected, get the Gtk::TreeView::Selection object from the TreeView, like so:

    auto refTreeSelection = m_TreeView.get_selection();

#### Seleção única ou múltipla

By default, only single rows can be selected, but you can allow multiple selection by setting the mode, like so:

    refTreeSelection->set_mode(Gtk::SelectionMode::MULTIPLE);

#### As linhas selecionadas

For single-selection, you can just call get_selected(), like so:

    auto iter = refTreeSelection->get_selected();
    if(iter) //If anything is selected
    {
      auto row = *iter;
      //Do something with the row.
    }

For multiple-selection, you need to call get_selected_rows() or define a callback, and give it to selected_foreach(), selected_foreach_path(), or selected_foreach_iter(), like so:

    refTreeSelection->selected_foreach_iter(
        sigc::mem_fun(*this, &TheClass::selected_row_callback) );

    void TheClass::selected_row_callback(
        const Gtk::TreeModel::const_iterator& iter)
    {
      auto row = *iter;
      //Do something with the row.
    }

#### O sinal "changed"

To respond to the user clicking on a row or range of rows, connect to the signal like so:

    refTreeSelection->signal_changed().connect(
        sigc::mem_fun(*this, &Example_IconTheme::on_selection_changed)
    );

#### Impedindo a seleção de linhas

Maybe the user should not be able to select every item in your list or tree. For instance, in the gtk-demo, you can select a demo to see the source code, but it doesn't make any sense to select a demo category.

To control which rows can be selected, use the set_select_function() method, providing a sigc::slot callback. For instance:

    m_refTreeSelection->set_select_function( sigc::mem_fun(*this,
        &DemoWindow::select_function) );

e, em seguida,

    bool DemoWindow::select_function(
        const Glib::RefPtr<Gtk::TreeModel>& model,
        const Gtk::TreeModel::Path& path, bool)
    {
      const auto iter = model->get_iter(path);
      return iter->children().empty(); // only allow leaf nodes to be selected
    }

#### Alterando a seleção

To change the selection, specify a Gtk::TreeModel::iterator or Gtk::TreeModel::Row, like so:

    auto row = m_refModel->children()[5]; //The sixth row.
    if(row)
      refTreeSelection->select(row.get_iter());

ou

    auto iter = m_refModel->children().begin()
    if(iter)
      refTreeSelection->select(iter);

### Classificando

The standard tree models (TreeStore and ListStore) derive from TreeSortable, so they offer sorting functionality. For instance, call set_sort_column(), to sort the model by the specified column. Or supply a callback function to set_sort_func() to implement a more complicated sorting algorithm.

TreeSortable Reference

#### Sorting by clicking on columns

So that a user can click on a TreeView's column header to sort the TreeView's contents, call Gtk::TreeView::Column::set_sort_column(), supplying the model column on which model should be sorted when the header is clicked. For instance:

    auto pColumn = treeview.get_column(0);
    if(pColumn)
      pColumn->set_sort_column(m_columns.m_col_id);

#### Independently sorted views of the same model

The TreeView already allows you to show the same TreeModel in two TreeView widgets. If you need one of these TreeViews to sort the model differently than the other then you should use a TreeModelSort instead of just, for instance, Gtk::TreeViewColumn::set_sort_column(). TreeModelSort is a model that contains another model, presenting a sorted version of that model. For instance, you might add a sorted version of a model to a TreeView like so:

    auto sorted_model = Gtk::TreeModelSort::create(model);
    sorted_model->set_sort_column(columns.m_col_name, Gtk::SortType::ASCENDING);
    treeview.set_model(sorted_model);

Note, however, that the TreeView will provide iterators to the sorted model. You must convert them to iterators to the underlying child model in order to perform actions on that model. For instance:

    void ExampleWindow::on_button_delete()
    {
      auto refTreeSelection = m_treeview.get_selection();
      if(refTreeSelection)
      {
        auto sorted_iter = m_refTreeSelection->get_selected();
        if(sorted_iter)
        {
          auto iter = m_refModelSort->convert_iter_to_child_iter(sorted_iter);
          m_refModel->erase(iter);
        }
      }
    }

TreeModelSort Reference

### Arrastar e soltar

Gtk::TreeView already implements simple drag-and-drop when used with the Gtk::ListStore or Gtk::TreeStore models (since gtk 4.8). If necessary, it also allows you to implement more complex behavior when items are dragged and dropped, using the normal Drag and Drop API.

#### Linhas reordenáveis

If you call Gtk::TreeView::set_reorderable() then your TreeView's items can be moved within the treeview itself. This is demonstrated in the TreeStore example.

However, this does not allow you any control of which items can be dragged, and where they can be dropped. If you need that extra control then you might create a derived `Gtk::TreeModel` from `Gtk::TreeStore` or `Gtk::ListStore` and override the `Gtk::TreeDragSource::row_draggable_vfunc()` and `Gtk::TreeDragDest::row_drop_possible_vfunc()` virtual methods. You can examine the `Gtk::TreeModel::Path`s provided and allow or disallow dragging or dropping by returning `true` or `false`.

This is demonstrated in the drag_and_drop example.

### Contexto de menu popup

Lots of people need to implement right-click context menus for TreeViews so we will explain how to do that here to save you some time. It's much the same as a normal context menu, as described in the menus chapter. You use a Gtk::GestureClick to detect the mouse click.

This is demonstrated in the Popup Context Menu example. In that example a derived TreeView is used, but that's not necessary.

### Examples

Some TreeView examples are shown here. There are more examples in the treeview directory in gtkmm-documentation's examples.

If neither ListStore nor TreeStore is suitable for your application, look at the custom TreeModel example. It shows how you can make your own implementation of the TreeModel interface.

#### ListStore

This example has a Gtk::TreeView widget, with a Gtk::ListStore model.

TreeView - ListStore

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_quit();

      //Tree model columns:
      class ModelColumns : public Gtk::TreeModel::ColumnRecord
      {
      public:

        ModelColumns()
        { add(m_col_id); add(m_col_name); add(m_col_number); add(m_col_percentage);}

        Gtk::TreeModelColumn<unsigned int> m_col_id;
        Gtk::TreeModelColumn<Glib::ustring> m_col_name;
        Gtk::TreeModelColumn<short> m_col_number;
        Gtk::TreeModelColumn<int> m_col_percentage;
      };

      ModelColumns m_Columns;

      //Child widgets:
      Gtk::Box m_VBox;

      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::TreeView m_TreeView;
      Glib::RefPtr<Gtk::ListStore> m_refTreeModel;

      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include <iostream>
    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::TreeView (ListStore) example");
      set_default_size(400, 200);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      //Add the TreeView, inside a ScrolledWindow, with the button underneath:
      m_ScrolledWindow.set_child(m_TreeView);

      //Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(5);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_button_quit) );

      //Create the Tree model:
      m_refTreeModel = Gtk::ListStore::create(m_Columns);
      m_TreeView.set_model(m_refTreeModel);

      //Fill the TreeView's model
      auto row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 1;
      row[m_Columns.m_col_name] = "Billy Bob";
      row[m_Columns.m_col_number] = 10;
      row[m_Columns.m_col_percentage] = 15;

      row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 2;
      row[m_Columns.m_col_name] = "Joey Jojo";
      row[m_Columns.m_col_number] = 20;
      row[m_Columns.m_col_percentage] = 40;

      row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 3;
      row[m_Columns.m_col_name] = "Rob McRoberts";
      row[m_Columns.m_col_number] = 30;
      row[m_Columns.m_col_percentage] = 70;

      //Add the TreeView's view columns:
      //This number will be shown with the default numeric formatting.
      m_TreeView.append_column("ID", m_Columns.m_col_id);
      m_TreeView.append_column("Name", m_Columns.m_col_name);

      m_TreeView.append_column_numeric("Formatted number", m_Columns.m_col_number,
              "%010d" /* 10 digits, using leading zeroes. */);

      //Display a progress bar instead of a decimal number:
      auto cell = Gtk::make_managed<Gtk::CellRendererProgress>();
      int cols_count = m_TreeView.append_column("Some percentage", *cell);
      auto pColumn = m_TreeView.get_column(cols_count - 1);
      if(pColumn)
      {
        pColumn->add_attribute(cell->property_value(), m_Columns.m_col_percentage);
      }

      //Make all the columns reorderable:
      //This is not necessary, but it's nice to show the feature.
      //You can use TreeView::set_column_drag_function() to more
      //finely control column drag and drop.
      for(guint i = 0; i < 2; i++)
      {
        auto column = m_TreeView.get_column(i);
        column->set_reorderable();
      }
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### TreeStore

This example is very similar to the ListStore example, but uses a Gtk::TreeStore model instead, and adds children to the rows.

TreeView - TreeStore

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_quit();
      void on_treeview_row_activated(const Gtk::TreeModel::Path& path, Gtk::TreeViewColumn* column);

      //Tree model columns:
      class ModelColumns : public Gtk::TreeModel::ColumnRecord
      {
      public:

        ModelColumns()
        { add(m_col_id); add(m_col_name); }

        Gtk::TreeModelColumn<int> m_col_id;
        Gtk::TreeModelColumn<Glib::ustring> m_col_name;
      };

      ModelColumns m_Columns;

      //Child widgets:
      Gtk::Box m_VBox;

      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::TreeView m_TreeView;
      Glib::RefPtr<Gtk::TreeStore> m_refTreeModel;

      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include <iostream>
    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::TreeView (TreeStore) example");
      set_default_size(400, 200);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      //Add the TreeView, inside a ScrolledWindow, with the button underneath:
      m_ScrolledWindow.set_child(m_TreeView);

      //Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(5);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_quit) );

      //Create the Tree model:
      m_refTreeModel = Gtk::TreeStore::create(m_Columns);
      m_TreeView.set_model(m_refTreeModel);

      //All the items to be reordered with drag-and-drop:
      m_TreeView.set_reorderable();

      //Fill the TreeView's model
      auto row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 1;
      row[m_Columns.m_col_name] = "Billy Bob";

      auto childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_Columns.m_col_id] = 11;
      childrow[m_Columns.m_col_name] = "Billy Bob Junior";

      childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_Columns.m_col_id] = 12;
      childrow[m_Columns.m_col_name] = "Sue Bob";

      row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 2;
      row[m_Columns.m_col_name] = "Joey Jojo";

      row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 3;
      row[m_Columns.m_col_name] = "Rob McRoberts";

      childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_Columns.m_col_id] = 31;
      childrow[m_Columns.m_col_name] = "Xavier McRoberts";

      //Add the TreeView's view columns:
      m_TreeView.append_column("ID", m_Columns.m_col_id);
      m_TreeView.append_column("Name", m_Columns.m_col_name);

      //Connect signal:
      m_TreeView.signal_row_activated().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_treeview_row_activated) );
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void ExampleWindow::on_treeview_row_activated(const Gtk::TreeModel::Path& path,
            Gtk::TreeViewColumn* /* column */)
    {
      const auto iter = m_refTreeModel->get_iter(path);
      if(iter)
      {
        const auto row = *iter;
        std::cout << "Row activated: ID=" << row[m_Columns.m_col_id] << ", Name="
            << row[m_Columns.m_col_name] << std::endl;
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Células editáveis

This example is identical to the ListStore example, but it uses TreeView::append_column_editable() instead of TreeView::append_column().

TreeView - Células editáveis

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_quit();

      void treeviewcolumn_validated_on_cell_data(Gtk::CellRenderer* renderer, const Gtk::TreeModel::const_iterator& iter);
      void cellrenderer_validated_on_editing_started(Gtk::CellEditable* cell_editable, const Glib::ustring& path);
      void cellrenderer_validated_on_edited(const Glib::ustring& path_string, const Glib::ustring& new_text);
      void on_message_response(int response_id, Gtk::MessageDialog* dialog);

      //Tree model columns:
      class ModelColumns : public Gtk::TreeModel::ColumnRecord
      {
      public:

        ModelColumns()
        { add(m_col_id); add(m_col_name); add(m_col_foo); add(m_col_number); add(m_col_number_validated); }

        Gtk::TreeModelColumn<unsigned int> m_col_id;
        Gtk::TreeModelColumn<Glib::ustring> m_col_name;
        Gtk::TreeModelColumn<bool> m_col_foo;
        Gtk::TreeModelColumn<int> m_col_number;
        Gtk::TreeModelColumn<int> m_col_number_validated;
      };

      ModelColumns m_Columns;

      //Child widgets:
      Gtk::Box m_VBox;

      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::TreeView m_TreeView;
      Glib::RefPtr<Gtk::ListStore> m_refTreeModel;

      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;

      //For the validated column:
      //You could also use a CellRendererSpin or a CellRendererProgress:
      Gtk::CellRendererText m_cellrenderer_validated;
      Gtk::TreeView::Column m_treeviewcolumn_validated;
      bool m_validate_retry;
      Glib::ustring m_invalid_text_for_retry;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include <iostream>
    #include <cstdio>
    #include <cstdlib>
    #include "examplewindow.h"

    using std::sprintf;
    using std::strtol;

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Quit("Quit"),
      m_validate_retry(false)
    {
      set_title("Gtk::TreeView Editable Cells example");
      set_default_size(400, 200);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      //Add the TreeView, inside a ScrolledWindow, with the button underneath:
      m_ScrolledWindow.set_child(m_TreeView);

      //Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(5);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_button_quit) );

      //Create the Tree model:
      m_refTreeModel = Gtk::ListStore::create(m_Columns);
      m_TreeView.set_model(m_refTreeModel);

      //Fill the TreeView's model
      auto row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 1;
      row[m_Columns.m_col_name] = "Billy Bob";
      row[m_Columns.m_col_foo] = true;
      row[m_Columns.m_col_number] = 10;

      row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 2;
      row[m_Columns.m_col_name] = "Joey Jojo";
      row[m_Columns.m_col_foo] = true;
      row[m_Columns.m_col_number] = 20;

      row = *(m_refTreeModel->append());

      row[m_Columns.m_col_id] = 3;
      row[m_Columns.m_col_name] = "Rob McRoberts";
      row[m_Columns.m_col_foo] = false;
      row[m_Columns.m_col_number] = 30;

      //Add the TreeView's view columns:
      //We use the *_editable convenience methods for most of these,
      //because the default functionality is enough:
      m_TreeView.append_column_editable("ID", m_Columns.m_col_id);
      m_TreeView.append_column_editable("Name", m_Columns.m_col_name);
      m_TreeView.append_column_editable("foo", m_Columns.m_col_foo);
      m_TreeView.append_column_numeric_editable("Number", m_Columns.m_col_number,
              "%010d");

      //For this column, we create the CellRenderer ourselves, and connect our own
      //signal handlers, so that we can validate the data that the user enters, and
      //control how it is displayed.
      m_treeviewcolumn_validated.set_title("validated (<10)");
      m_treeviewcolumn_validated.pack_start(m_cellrenderer_validated);
      m_TreeView.append_column(m_treeviewcolumn_validated);

      //Tell the view column how to render the model values:
      m_treeviewcolumn_validated.set_cell_data_func(m_cellrenderer_validated,
              sigc::mem_fun(*this,
                  &ExampleWindow::treeviewcolumn_validated_on_cell_data) );

      //Make the CellRenderer editable, and handle its editing signals:
      m_cellrenderer_validated.property_editable() = true;

      m_cellrenderer_validated.signal_editing_started().connect(
              sigc::mem_fun(*this,
            &ExampleWindow::cellrenderer_validated_on_editing_started) );

      m_cellrenderer_validated.signal_edited().connect( sigc::mem_fun(*this,
                  &ExampleWindow::cellrenderer_validated_on_edited) );

      //If this was a CellRendererSpin then you would have to set the adjustment:
      //m_cellrenderer_validated.property_adjustment() = m_spin_adjustment;
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void ExampleWindow::treeviewcolumn_validated_on_cell_data(
            Gtk::CellRenderer* /* renderer */,
            const Gtk::TreeModel::const_iterator& iter)
    {
      //Get the value from the model and show it appropriately in the view:
      if(iter)
      {
        const auto row = *iter;
        int model_value = row[m_Columns.m_col_number_validated];

        //This is just an example.
        //In this case, it would be easier to use append_column_editable() or
        //append_column_numeric_editable()
        char buffer[32];
        sprintf(buffer, "%d", model_value);

        auto view_text = buffer;
        m_cellrenderer_validated.property_text() = view_text;
      }
    }

    void ExampleWindow::cellrenderer_validated_on_editing_started(
            Gtk::CellEditable* cell_editable, const Glib::ustring& /* path */)
    {
      //Start editing with previously-entered (but invalid) text,
      //if we are allowing the user to correct some invalid data.
      if(m_validate_retry)
      {
        //This is the CellEditable inside the CellRenderer.
        auto celleditable_validated = cell_editable;

        //It's usually an Entry, at least for a CellRendererText:
        auto pEntry = dynamic_cast<Gtk::Entry*>(celleditable_validated);
        if(pEntry)
        {
          pEntry->set_text(m_invalid_text_for_retry);
          m_validate_retry = false;
          m_invalid_text_for_retry.clear();
        }
      }
    }

    void ExampleWindow::cellrenderer_validated_on_edited(
            const Glib::ustring& path_string,
            const Glib::ustring& new_text)
    {
      Gtk::TreePath path(path_string);

      //Convert the inputed text to an integer, as needed by our model column:
      char* pchEnd = nullptr;
      int new_value = strtol(new_text.c_str(), &pchEnd, 10);

      if(new_value >= 10)
      {
        //Prevent entry of numbers higher than 10.

        //Tell the user:
        auto dialog = new Gtk::MessageDialog(*this,
                "The number must be less than 10. Please try again.",
                false, Gtk::MessageType::ERROR, Gtk::ButtonsType::OK, true /* modal */);
        dialog->signal_response().connect(sigc::bind(
          sigc::mem_fun(*this, &ExampleWindow::on_message_response), dialog));

        dialog->set_visible(true);

        //Start editing again, with the bad text, so that the user can correct it.
        //A real application should probably allow the user to revert to the
        //previous text.

        //Set the text to be used in the start_editing signal handler:
        m_invalid_text_for_retry = new_text;
        m_validate_retry = true;

        //Start editing again, when the message dialog has been closed:
        m_TreeView.set_cursor(path, m_treeviewcolumn_validated,
                m_cellrenderer_validated, true /* start_editing */);
      }
      else
      {
        //Get the row from the path:
        auto iter = m_refTreeModel->get_iter(path);
        if(iter)
        {
          auto row = *iter;

          //Put the new value in the model:
          row[m_Columns.m_col_number_validated] = new_value;
        }
      }
    }

    void ExampleWindow::on_message_response(int /* response_id */, Gtk::MessageDialog* dialog)
    {
      delete dialog;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Arrastar e soltar

This example is much like the TreeStore example, but has 2 extra columns to indicate whether the row can be dragged, and whether it can receive drag-and-dropped rows. It uses a derived Gtk::TreeStore which overrides the virtual functions as described in the TreeView Drag and Drop section.

TreeView - Arrastar e soltar

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>
    #include "treemodel_dnd.h"

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_quit();

      //Child widgets:
      Gtk::Box m_VBox;

      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::TreeView m_TreeView;
      Glib::RefPtr<TreeModel_Dnd> m_refTreeModel;

      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `treemodel_dnd.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_TREEMODEL_DND_H
    #define GTKMM_EXAMPLE_TREEMODEL_DND_H

    #include <gtkmm.h>

    class TreeModel_Dnd : public Gtk::TreeStore
    {
    protected:
      TreeModel_Dnd();

    public:

      //Tree model columns:
      class ModelColumns : public Gtk::TreeModel::ColumnRecord
      {
      public:

        ModelColumns()
        { add(m_col_id); add(m_col_name); add(m_col_draggable); add(m_col_receivesdrags); }

        Gtk::TreeModelColumn<int> m_col_id;
        Gtk::TreeModelColumn<Glib::ustring> m_col_name;
        Gtk::TreeModelColumn<bool> m_col_draggable;
        Gtk::TreeModelColumn<bool> m_col_receivesdrags;
      };

      ModelColumns m_Columns;

      static Glib::RefPtr<TreeModel_Dnd> create();

    protected:
      //Overridden virtual functions:
      bool row_draggable_vfunc(const Gtk::TreeModel::Path& path) const override;
      bool row_drop_possible_vfunc(const Gtk::TreeModel::Path& dest, const Glib::ValueBase& value) const override;
    };

    #endif //GTKMM_EXAMPLE_TREEMODEL_DND_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include <iostream>
    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Quit("_Quit", true)
    {
      set_title("Gtk::TreeView (Drag and Drop) example");
      set_default_size(400, 200);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      //Add the TreeView, inside a ScrolledWindow, with the button underneath:
      m_ScrolledWindow.set_child(m_TreeView);

      //Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(5);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_quit) );

      //Create the Tree model:
      //Use our derived model, which overrides some Gtk::TreeDragDest and
      //Gtk::TreeDragSource virtual functions:
      //The columns are declared in the overridden TreeModel.
      m_refTreeModel = TreeModel_Dnd::create();
      m_TreeView.set_model(m_refTreeModel);

      //Enable Drag-and-Drop of TreeView rows:
      //See also the derived TreeModel's *_vfunc overrides.
      m_TreeView.enable_model_drag_source();
      m_TreeView.enable_model_drag_dest();

      //Fill the TreeView's model
      auto row = *(m_refTreeModel->append());
      row[m_refTreeModel->m_Columns.m_col_id] = 1;
      row[m_refTreeModel->m_Columns.m_col_name] = "Billy Bob";
      row[m_refTreeModel->m_Columns.m_col_draggable] = true;
      row[m_refTreeModel->m_Columns.m_col_receivesdrags] = true;

      auto childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_refTreeModel->m_Columns.m_col_id] = 11;
      childrow[m_refTreeModel->m_Columns.m_col_name] = "Billy Bob Junior";
      childrow[m_refTreeModel->m_Columns.m_col_draggable] = true;
      childrow[m_refTreeModel->m_Columns.m_col_receivesdrags] = true;

      childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_refTreeModel->m_Columns.m_col_id] = 12;
      childrow[m_refTreeModel->m_Columns.m_col_name] = "Sue Bob";
      childrow[m_refTreeModel->m_Columns.m_col_draggable] = true;
      childrow[m_refTreeModel->m_Columns.m_col_receivesdrags] = true;

      row = *(m_refTreeModel->append());
      row[m_refTreeModel->m_Columns.m_col_id] = 2;
      row[m_refTreeModel->m_Columns.m_col_name] = "Joey Jojo";
      row[m_refTreeModel->m_Columns.m_col_draggable] = true;
      row[m_refTreeModel->m_Columns.m_col_receivesdrags] = true;

      row = *(m_refTreeModel->append());
      row[m_refTreeModel->m_Columns.m_col_id] = 3;
      row[m_refTreeModel->m_Columns.m_col_name] = "Rob McRoberts";
      row[m_refTreeModel->m_Columns.m_col_draggable] = true;
      row[m_refTreeModel->m_Columns.m_col_receivesdrags] = true;

      childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_refTreeModel->m_Columns.m_col_id] = 31;
      childrow[m_refTreeModel->m_Columns.m_col_name] = "Xavier McRoberts";
      childrow[m_refTreeModel->m_Columns.m_col_draggable] = true;
      childrow[m_refTreeModel->m_Columns.m_col_receivesdrags] = true;

      //Add the TreeView's view columns:
      m_TreeView.append_column("ID", m_refTreeModel->m_Columns.m_col_id);
      m_TreeView.append_column("Name", m_refTreeModel->m_Columns.m_col_name);
      m_TreeView.append_column_editable("Draggable",
              m_refTreeModel->m_Columns.m_col_draggable);
      m_TreeView.append_column_editable("Receives Drags",
              m_refTreeModel->m_Columns.m_col_receivesdrags);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `treemodel_dnd.cc` (For use with gtkmm 4)

    #include "treemodel_dnd.h"
    #include <iostream>

    TreeModel_Dnd::TreeModel_Dnd()
    {
      //We can't just call Gtk::TreeModel(m_Columns) in the initializer list
      //because m_Columns does not exist when the base class constructor runs.
      //And we can't have a static m_Columns instance, because that would be
      //instantiated before the gtkmm type system.
      //So, we use this method, which should only be used just after creation:
      set_column_types(m_Columns);
    }

    Glib::RefPtr<TreeModel_Dnd> TreeModel_Dnd::create()
    {
      return Glib::make_refptr_for_instance<TreeModel_Dnd>( new TreeModel_Dnd() );
    }

    bool
    TreeModel_Dnd::row_draggable_vfunc(const Gtk::TreeModel::Path& path) const
    {
      // Make the value of the "draggable" column determine whether this row can
      // be dragged:

      const const_iterator iter = get_iter(path);
      if(iter)
      {
        ConstRow row = *iter;
        bool is_draggable = row[m_Columns.m_col_draggable];
        return is_draggable;
      }

      return Gtk::TreeStore::row_draggable_vfunc(path);
    }

    bool
    TreeModel_Dnd::row_drop_possible_vfunc(const Gtk::TreeModel::Path& dest,
            const Glib::ValueBase& value) const
    {
      //Make the value of the "receives drags" column determine whether a row can be
      //dragged into it:

      //dest is the path that the row would have after it has been dropped:
      //But in this case we are more interested in the parent row:
      auto dest_parent = dest;
      bool dest_is_not_top_level = dest_parent.up();
      if(!dest_is_not_top_level || dest_parent.empty())
      {
        //The user wants to move something to the top-level.
        //Let's always allow that.
      }
      else
      {
        //Get an iterator for the row at this path:
        const const_iterator iter_dest_parent = get_iter(dest_parent);
        if(iter_dest_parent)
        {
          ConstRow row = *iter_dest_parent;
          bool receives_drags = row[m_Columns.m_col_receivesdrags];
          return receives_drags;
        }
      }

      // You could also examine the row being dragged (via value)
      // if you must look at both rows to see whether a drop should be allowed.
      // You could use
      //   Glib::RefPtr<const Gtk::TreeModel> model_dragged_row;
      //   Gtk::TreeModel::Path path_dragged_row;
      //   Gtk::TreeModel::Path::get_row_drag_data(value,
      //     model_dragged_row, path_dragged_row);

      return Gtk::TreeStore::row_drop_possible_vfunc(dest, value);
    }

#### Contexto de menu popup

This example is much like the ListStore example, but derives a custom TreeView to encapsulate the tree model code and popup menu code in our derived class. See the TreeView Popup Context Menu section.

TreeView - Contexto de menu popup

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>
    #include "treeview_withpopup.h"

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_quit();

      //Child widgets:
      Gtk::Box m_VBox;

      Gtk::ScrolledWindow m_ScrolledWindow;
      TreeView_WithPopup m_TreeView;

      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `treeview_withpopup.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_TREEVIEW_WITHPOPUP_H
    #define GTKMM_EXAMPLE_TREEVIEW_WITHPOPUP_H

    #include <gtkmm.h>

    class TreeView_WithPopup : public Gtk::TreeView
    {
    public:
      TreeView_WithPopup();
      virtual ~TreeView_WithPopup();

    protected:
      // Signal handler for showing popup menu:
      void on_popup_button_pressed(int n_press, double x, double y);

      //Signal handler for popup menu items:
      void on_menu_file_popup_generic();

      //Tree model columns:
      class ModelColumns : public Gtk::TreeModel::ColumnRecord
      {
      public:

        ModelColumns()
        { add(m_col_id); add(m_col_name); }

        Gtk::TreeModelColumn<unsigned int> m_col_id;
        Gtk::TreeModelColumn<Glib::ustring> m_col_name;
      };

      ModelColumns m_Columns;

      //The Tree model:
      Glib::RefPtr<Gtk::ListStore> m_refTreeModel;

      Gtk::PopoverMenu m_MenuPopup;
    };

    #endif //GTKMM_EXAMPLE_TREEVIEW_WITHPOPUP_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include <iostream>
    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::TreeView (ListStore) example");
      set_default_size(400, 200);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      //Add the TreeView, inside a ScrolledWindow, with the button underneath:
      m_ScrolledWindow.set_child(m_TreeView);

      //Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(5);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_button_quit) );
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `treeview_withpopup.cc` (For use with gtkmm 4)

    #include "treeview_withpopup.h"
    #include <iostream>

    TreeView_WithPopup::TreeView_WithPopup()
    {
      //Create the Tree model:
      m_refTreeModel = Gtk::ListStore::create(m_Columns);
      set_model(m_refTreeModel);

      //Fill the TreeView's model
      auto row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 1;
      row[m_Columns.m_col_name] = "right-click on this";

      row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 2;
      row[m_Columns.m_col_name] = "or this";

      row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 3;
      row[m_Columns.m_col_name] = "or this, for a popup context menu";

      //Add the TreeView's view columns:
      append_column("ID", m_Columns.m_col_id);
      append_column("Name", m_Columns.m_col_name);

      // Catch button press events:
      auto refGesture = Gtk::GestureClick::create();
      refGesture->set_button(GDK_BUTTON_SECONDARY);
      refGesture->signal_pressed().connect(
        sigc::mem_fun(*this, &TreeView_WithPopup::on_popup_button_pressed));
      add_controller(refGesture);

      // Fill popup menu:
      auto gmenu = Gio::Menu::create();
      gmenu->append("_Edit", "popup.edit");
      gmenu->append("_Process", "popup.process");
      gmenu->append("_Remove", "popup.remove");

      m_MenuPopup.set_parent(*this);
      m_MenuPopup.set_menu_model(gmenu);
      m_MenuPopup.set_has_arrow(false);

      // Create actions:
      auto refActionGroup = Gio::SimpleActionGroup::create();

      refActionGroup->add_action("edit",
        sigc::mem_fun(*this, &TreeView_WithPopup::on_menu_file_popup_generic));
      refActionGroup->add_action("process",
        sigc::mem_fun(*this, &TreeView_WithPopup::on_menu_file_popup_generic));
      refActionGroup->add_action("remove",
        sigc::mem_fun(*this, &TreeView_WithPopup::on_menu_file_popup_generic));

      insert_action_group("popup", refActionGroup);
    }

    TreeView_WithPopup::~TreeView_WithPopup()
    {
    }

    void TreeView_WithPopup::on_popup_button_pressed(int /* n_press */, double x, double y)
    {
      const Gdk::Rectangle rect(x, y, 1, 1);
      m_MenuPopup.set_pointing_to(rect);
      m_MenuPopup.popup();
    }

    void TreeView_WithPopup::on_menu_file_popup_generic()
    {
      std::cout << "A popup menu item was selected." << std::endl;

      auto refSelection = get_selection();
      if(refSelection)
      {
        auto iter = refSelection->get_selected();
        if(iter)
        {
          int id = (*iter)[m_Columns.m_col_id];
          std::cout << "  Selected ID=" << id << std::endl;
        }
      }
    }

## The DropDown Widget

The DropDown widget is an alternative to the deprecated ComboBox. It uses list models instead of tree models, and the content is displayed using widgets instead of cell renderers.

The DropDown widget offers a list of choices in a dropdown menu. If appropriate, it can show extra information about each item, such as text, a picture, or a check button. The DropDown widget can optionally have an Entry in the dropdown menu, allowing the user to search in a long list.

The list is provided via a Gio::ListModel, and data from this model is added to the DropDown's view with signal handlers connected to a SignalListItemFactory. This provides flexibility, but the StringList class provides a simpler text-based specialization in case that flexibility is not required.

Reference

### O modelo

The model for a DropDown can be defined and filled exactly as for a ListView or a ColumnView. It must be a subclass of Glib::Object. For instance, you might have a DropDown with one integer and one text column, like so:

    class ModelColumns : public Glib::Object
    {
    public:
      int m_col_id;
      Glib::ustring m_col_name;

      static Glib::RefPtr<ModelColumns> create(
        int col_id, const Glib::ustring& col_name)
      {
        return Glib::make_refptr_for_instance<ModelColumns>(
          new ModelColumns(col_id, col_name));
      }

    protected:
      ModelColumns(int col_id, const Glib::ustring& col_name)
      : m_col_id(col_id), m_col_name(col_name)
      {}
    };

    Glib::RefPtr<Gio::ListStore<ModelColumns>> m_ListStore;

After appending rows to this model, you should provide the model to the DropDown with the set_model() method. Unless you use the StringList model, you also need to set a ListItemFactory with set_factory(). If you want the items in the dropdown menu to look different from the item in the DropDown widget, you also need to set a separate ListItemFactory with set_list_factory().

### The selected item

To discover what item, if any, the user has selected from the DropDown, call DropDown::get_selected(). This returns an unsigned int that you can use to get the selected data from the model. For instance, you might read an integer ID value from the model, even though you have chosen only to show the human-readable description in the DropDown. For instance:

    unsigned int sel = m_DropDown.get_selected();
    if (sel != GTK_INVALID_LIST_POSITION)
    {
      // Get the data for the selected row, using our knowledge of the list model:
      auto id = m_ListStore->get_item(sel).m_col_id;
      set_some_id_chosen(id); // Your own function.
    }
    else
      set_nothing_chosen(); // Your own function.

### Respondendo as mudanças

You might need to react to every change of selection in the DropDown, for instance to update other widgets. To do so, you should connect to property_selected().signal_changed(). For instance:

    m_DropDown.property_selected().signal_changed().connect(
      sigc::mem_fun(*this, &ExampleWindow::on_dropdown_changed));

### Simple String Example

Simple DropDown

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm/window.h>
    #include <gtkmm/dropdown.h>
    #include <gtkmm/stringlist.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      // Signal handler:
      void on_dropdown_changed();

      // Child widget:
      Gtk::DropDown m_DropDown;

      Glib::RefPtr<Gtk::StringList> m_StringList;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    {
      set_title("DropDown example");

      set_child(m_DropDown);

      // Fill the dropdown:
      const std::vector<Glib::ustring> strings{
        "1 minute", "2 minutes", "5 minutes", "20 minutes"
      };
      m_StringList = Gtk::StringList::create(strings);
      m_DropDown.set_model(m_StringList);
      m_DropDown.set_selected(0);

      // Connect signal handler:
      m_DropDown.property_selected().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_dropdown_changed));
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_dropdown_changed()
    {
      const auto selected = m_DropDown.get_selected();
      std::cout << "DropDown changed: Row=" << selected
        << ", String=" << m_StringList->get_string(selected) << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Examples with a Search Entry

The dropdown menu may contain an Entry that allows to search for items in the list. Call set_enable_search() and set_expression(). For instance:

    m_DropDown.set_enable_search(true);
    auto expression = Gtk::ClosureExpression<Glib::ustring>::create(
      sigc::mem_fun(*this, &ExampleWindow::get_col_name));
    m_DropDown.set_expression(expression);

    //-------
    Glib::ustring ExampleWindow::get_col_name(const Glib::RefPtr<Glib::ObjectBase>& item)
    {
      const auto col = std::dynamic_pointer_cast<ModelColumns>(item);
      return col ? col->m_col_name : "";
    }

#### String Example

Search String

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm/window.h>
    #include <gtkmm/dropdown.h>
    #include <gtkmm/stringlist.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      // Signal handler:
      void on_dropdown_changed();

      // Child widget:
      Gtk::DropDown m_DropDown;

      Glib::RefPtr<Gtk::StringList> m_StringList;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/expression.h>
    #include <gtkmm/stringobject.h>
    #include <iostream>

    ExampleWindow::ExampleWindow()
    {
      set_title("Searchable DropDown example");

      set_child(m_DropDown);

      // Fill the dropdown:
      const std::vector<Glib::ustring> many_times{
        "1 minute", "2 minutes", "5 minutes", "10 minutes", "15 minutes", "20 minutes",
        "25 minutes", "30 minutes", "35 minutes", "40 minutes", "45 minutes", "50 minutes",
        "55 minutes", "1 hour", "2 hours", "3 hours", "5 hours", "6 hours", "7 hours",
        "8 hours", "9 hours", "10 hours", "11 hours", "12 hours"
      };
      m_StringList = Gtk::StringList::create(many_times);
      m_DropDown.set_model(m_StringList);
      m_DropDown.set_selected(0);

      // Show a search entry.
      m_DropDown.set_enable_search(true);
      auto expression = Gtk::ClosureExpression<Glib::ustring>::create(
        [](const Glib::RefPtr<Glib::ObjectBase>& item)->Glib::ustring
        {
          // An item in a StringList is a StringObject.
          const auto string_object = std::dynamic_pointer_cast<Gtk::StringObject>(item);
          return string_object ? string_object->get_string() : "";
        });
      m_DropDown.set_expression(expression);

      // Connect signal handler:
      m_DropDown.property_selected().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_dropdown_changed));
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_dropdown_changed()
    {
      const auto selected = m_DropDown.get_selected();
      std::cout << "DropDown changed: Row=" << selected
        << ", String=" << m_StringList->get_string(selected) << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Font Example

This example uses a Pango::FontMap as its model. This is possible because Pango::FontMap implements the Gio::ListModel interface. Of course you can use a FontDialogButton instead.

Search Font

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      // Signal handler:
      void on_dropdown_changed();

      Glib::ustring get_family_name(const Glib::RefPtr<Glib::ObjectBase>& item);

      // Child widget:
      Gtk::DropDown m_DropDown;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <pangomm/cairofontmap.h>
    #include <iostream>
    //#include <typeinfo>

    ExampleWindow::ExampleWindow()
    {
      set_title("Searchable DropDown example");

      // Add the DropDown to the window.
      set_child(m_DropDown);

      // Show a search entry.
      m_DropDown.set_enable_search(true);
      auto expression = Gtk::ClosureExpression<Glib::ustring>::create(
        sigc::mem_fun(*this, &ExampleWindow::get_family_name));
      m_DropDown.set_expression(expression);

      // Pango::FontMap is a Gio::ListModel.
      auto model = Pango::CairoFontMap::get_default();
      m_DropDown.set_model(model);
      m_DropDown.set_selected(0);

      // Connect signal handler.
      m_DropDown.property_selected().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_dropdown_changed));
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_dropdown_changed()
    {
      const auto selected = m_DropDown.get_selected();
      const auto item = m_DropDown.get_selected_item();
      std::cout << "DropDown changed: Row=" << selected
        << ", Font=" << get_family_name(item) << std::endl;

      // Pango::FontMap is often a list of items of type Pango::FontFamily.
      // From the description of Pango::CairoFontMap: "The actual type of the font map
      // will depend on the particular font technology Cairo was compiled to use."
      // If get_family_name() does not return a family name, you can add
      // #include <typeinfo> and query the type of the items with:
      //   std::cout << typeid(*item.get()).name() << std::endl;
    }

    Glib::ustring ExampleWindow::get_family_name(const Glib::RefPtr<Glib::ObjectBase>& item)
    {
      auto family = std::dynamic_pointer_cast<Pango::FontFamily>(item);
      return family ? family->get_name() : "";
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Complex Example

This is a more complex example with two SignalListItemFactory objects and their signal handlers. This example would be simpler without the checkmark in the dropdown menu.

Search Font

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      // Signal handlers:
      void on_setup_selected_item(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_selected_item(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_setup_list_item(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_bind_list_item(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_unbind_list_item(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_selected_item_changed(const Glib::RefPtr<Gtk::ListItem>& list_item);
      void on_dropdown_changed();

      void create_model();
      void liststore_add_item(const Glib::ustring& title, const Glib::ustring& icon,
        const Glib::ustring& description);

      // A Gio::ListStore item.
      class ModelColumns : public Glib::Object
      {
      public:
        Glib::ustring m_title;
        Glib::ustring m_icon;
        Glib::ustring m_description;

        static Glib::RefPtr<ModelColumns> create(const Glib::ustring& title,
          const Glib::ustring& icon, const Glib::ustring& description)
        {
          return Glib::make_refptr_for_instance<ModelColumns>(
            new ModelColumns(title, icon, description));
        }

      protected:
        ModelColumns(const Glib::ustring& title, const Glib::ustring& icon,
          const Glib::ustring& description)
        : m_title(title), m_icon(icon), m_description(description)
        {}
      }; // ModelColumns

      // Child widget:
      Gtk::DropDown m_DropDown;

      Glib::RefPtr<Gio::ListStore<ModelColumns>> m_ListStore;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    {
      set_title("DropDown example");

      // Add the DropDown to the window.
      set_child(m_DropDown);

      // Factory for presenting the selected item.
      auto factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_setup_selected_item));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_selected_item));
      m_DropDown.set_factory(factory);

      // Factory for presenting the items in the dropdown list.
      factory = Gtk::SignalListItemFactory::create();
      factory->signal_setup().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_setup_list_item));
      factory->signal_bind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_bind_list_item));
      factory->signal_unbind().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_unbind_list_item));
      m_DropDown.set_list_factory(factory);

      // Create the model and fill it.
      create_model();
      m_DropDown.set_model(m_ListStore);
      m_DropDown.set_selected(0);

      // Connect signal handler:
      m_DropDown.property_selected().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_dropdown_changed));
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_dropdown_changed()
    {
      const auto selected = m_DropDown.get_selected();
      std::cout << "DropDown changed: Row=" << selected
        << ", Title=" << m_ListStore->get_item(selected)->m_title << std::endl;
    }

    void ExampleWindow::create_model()
    {
      m_ListStore = Gio::ListStore<ModelColumns>::create();

      liststore_add_item("Digital Output", "audio-card-symbolic", "Built-in Audio");
      liststore_add_item("Headphones", "audio-headphones-symbolic", "Built-in Audio");
      liststore_add_item("Digital Output", "audio-card-symbolic", "Thinkpad Tunderbolt 3 Dock USB Audio");
      liststore_add_item("Analog Output", "audio-card-symbolic", "Thinkpad Tunderbolt 3 Dock USB Audio");
    }

    void ExampleWindow::liststore_add_item(const Glib::ustring& title,
      const Glib::ustring& icon, const Glib::ustring& description)
    {
      m_ListStore->append(ModelColumns::create(title, icon, description));
    }

    void ExampleWindow::on_setup_selected_item(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto box = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::HORIZONTAL, 10);
      box->append(*Gtk::make_managed<Gtk::Image>());
      box->append(*Gtk::make_managed<Gtk::Label>());
      list_item->set_child(*box);
    }

    void ExampleWindow::on_bind_selected_item(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(list_item->get_item());
      if (!col)
        return;
      auto box = dynamic_cast<Gtk::Box*>(list_item->get_child());
      if (!box)
        return;
      auto image = dynamic_cast<Gtk::Image*>(box->get_first_child());
      if (!image)
        return;
      image->set_from_icon_name(col->m_icon);
      auto label = dynamic_cast<Gtk::Label*>(image->get_next_sibling());
      if (!label)
        return;
      label->set_text(col->m_title);
    }

    void ExampleWindow::on_setup_list_item(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto hbox = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::HORIZONTAL, 10);
      auto vbox = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 2);

      hbox->append(*Gtk::make_managed<Gtk::Image>());
      hbox->append(*vbox);
      auto title = Gtk::make_managed<Gtk::Label>();
      title->set_xalign(0.0);
      vbox->append(*title);
      auto description = Gtk::make_managed<Gtk::Label>();
      description->set_xalign(0.0);
      description->add_css_class("dim-label");
      vbox->append(*description);
      auto checkmark = Gtk::make_managed<Gtk::Image>();
      checkmark->set_from_icon_name("object-select-symbolic");
      checkmark->set_visible(false);
      hbox->append(*checkmark);

      list_item->set_child(*hbox);
    }

    void ExampleWindow::on_bind_list_item(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto col = std::dynamic_pointer_cast<ModelColumns>(list_item->get_item());
      if (!col)
        return;
      auto hbox = dynamic_cast<Gtk::Box*>(list_item->get_child());
      if (!hbox)
        return;
      auto image = dynamic_cast<Gtk::Image*>(hbox->get_first_child());
      if (!image)
        return;
      image->set_from_icon_name(col->m_icon);
      auto vbox = dynamic_cast<Gtk::Box*>(image->get_next_sibling());
      if (!vbox)
        return;
      auto title = dynamic_cast<Gtk::Label*>(vbox->get_first_child());
      if (!title)
        return;
      title->set_text(col->m_title);
      auto description = dynamic_cast<Gtk::Label*>(title->get_next_sibling());
      if (!description)
        return;
      description->set_text(col->m_description);

      auto connection = m_DropDown.property_selected_item().signal_changed().connect(
        sigc::bind(sigc::mem_fun(*this, &ExampleWindow::on_selected_item_changed),
        list_item));
      list_item->set_data("connection", new sigc::connection(connection),
        Glib::destroy_notify_delete<sigc::connection>);
      on_selected_item_changed(list_item);
    }

    void ExampleWindow::on_unbind_list_item(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      if (auto connection = static_cast<sigc::connection*>(list_item->get_data("connection")))
      {
        connection->disconnect();
        list_item->set_data("connection", nullptr);
      }
    }

    void ExampleWindow::on_selected_item_changed(const Glib::RefPtr<Gtk::ListItem>& list_item)
    {
      auto hbox = dynamic_cast<Gtk::Box*>(list_item->get_child());
      if (!hbox)
        return;
      auto checkmark = dynamic_cast<Gtk::Image*>(hbox->get_last_child());
      if (!checkmark)
        return;
      checkmark->set_visible(m_DropDown.get_selected_item() == list_item->get_item());
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

## Caixa de combinação

Gtk::ComboBox and Gtk::ComboBoxText are deprecated since gtkmm 4.10. Use Gtk::DropDown in new code.

The ComboBox widget offers a list (or tree) of choices in a dropdown menu. If appropriate, it can show extra information about each item, such as text, a picture, a check button, or a progress bar. The ComboBox widget usually restricts the user to the available choices, but it can optionally have an Entry, allowing the user to enter arbitrary text if none of the available choices are suitable.

The list is provided via a TreeModel, and columns from this model are added to the ComboBox's view with the ComboBox::pack_start() method. This provides flexibility and compile-time type-safety, but the ComboBoxText class provides a simpler text-based specialization in case that flexibility is not required.

Reference

### O modelo

The model for a ComboBox can be defined and filled exactly as for a TreeView. For instance, you might derive a ComboBox class with one integer and one text column, like so:

    class ModelColumns : public Gtk::TreeModel::ColumnRecord
    {
    public:
      ModelColumns()
      { add(m_col_id); add(m_col_name); }

      Gtk::TreeModelColumn<int> m_col_id;
      Gtk::TreeModelColumn<Glib::ustring> m_col_name;
    };

    ModelColumns m_columns;

After appending rows to this model, you should provide the model to the ComboBox with the set_model() method. Then use the pack_start() or pack_end() methods to specify what columns will be displayed in the ComboBox. As with the TreeView you may either use the default cell renderer by passing the TreeModelColumn to the pack methods, or you may instantiate a specific CellRenderer and specify a particular mapping with either add_attribute() or set_cell_data_func(). Note that these methods are in the CellLayout base class.

### O item escolhido

To discover what item, if any, the user has chosen from the ComboBox, call ComboBox::get_active(). This returns a TreeModel::iterator that you can dereference to a Row in order to read the values in your columns. For instance, you might read an integer ID value from the model, even though you have chosen only to show the human-readable description in the ComboBox. For instance:

    Gtk::TreeModel::iterator iter = m_Combo.get_active();
    if(iter)
    {
      auto row = *iter;

      //Get the data for the selected row, using our knowledge
      //of the tree model:
      auto id = row[m_Columns.m_col_id];
      set_something_id_chosen(id); //Your own function.
    }
    else
      set_nothing_chosen(); //Your own function.

### Respondendo as mudanças

You might need to react to every change of selection in the ComboBox, for instance to update other widgets. To do so, you should handle the `changed` signal. For instance:

    m_combo.signal_changed().connect( sigc::mem_fun(*this,
          &ExampleWindow::on_combo_changed) );

### Exemplo completo

Caixa de combinação

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm/window.h>
    #include <gtkmm/comboboxtext.h>
    #include <gtkmm/liststore.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      void on_cell_data_extra(const Gtk::TreeModel::const_iterator& iter);

      //Signal handlers:
      void on_combo_changed();

      //Tree model columns:
      class ModelColumns : public Gtk::TreeModel::ColumnRecord
      {
      public:

        ModelColumns()
        { add(m_col_id); add(m_col_name); add(m_col_extra);}

        Gtk::TreeModelColumn<int> m_col_id;
        Gtk::TreeModelColumn<Glib::ustring> m_col_name;
        Gtk::TreeModelColumn<Glib::ustring> m_col_extra;
      };

      ModelColumns m_Columns;

      //Child widgets:
      Gtk::ComboBox m_Combo;
      Gtk::CellRendererText m_cell;
      Glib::RefPtr<Gtk::ListStore> m_refTreeModel;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    {
      set_title("ComboBox example");

      //Create the Tree model:
      //m_refTreeModel = Gtk::TreeStore::create(m_Columns);
      m_refTreeModel = Gtk::ListStore::create(m_Columns);
      m_Combo.set_model(m_refTreeModel);

      //Fill the ComboBox's Tree Model:
      auto iter = m_refTreeModel->append();
      auto row = *iter;
      row[m_Columns.m_col_id] = 1;
      row[m_Columns.m_col_name] = "Billy Bob";
      row[m_Columns.m_col_extra] = "something";
      m_Combo.set_active(iter);
      /*
      auto childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_Columns.m_col_id] = 11;
      childrow[m_Columns.m_col_name] = "Billy Bob Junior";

      childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_Columns.m_col_id] = 12;
      childrow[m_Columns.m_col_name] = "Sue Bob";
      */

      row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 2;
      row[m_Columns.m_col_name] = "Joey Jojo";
      row[m_Columns.m_col_extra] = "yadda";

      row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = 3;
      row[m_Columns.m_col_name] = "Rob McRoberts";
      row[m_Columns.m_col_extra] = "";

      /*
      childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_Columns.m_col_id] = 31;
      childrow[m_Columns.m_col_name] = "Xavier McRoberts";
      */

      //Add the model columns to the Combo (which is a kind of view),
      //rendering them in the default way:
      m_Combo.pack_start(m_Columns.m_col_id);
      m_Combo.pack_start(m_Columns.m_col_name);

      //An example of adding a cell renderer manually,
      //instead of using pack_start(model_column, Gtk::PackOptions::EXPAND_WIDGET)
      //so we have more control:
      m_Combo.set_cell_data_func(m_cell,
        sigc::mem_fun(*this, &ExampleWindow::on_cell_data_extra));
      m_Combo.pack_start(m_cell);

      //Add the ComboBox to the window.
      set_child(m_Combo);

      //Connect signal handler:
      m_Combo.signal_changed().connect( sigc::mem_fun(*this, &ExampleWindow::on_combo_changed) );
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_cell_data_extra(const Gtk::TreeModel::const_iterator& iter)
    {
      auto row = *iter;
      const Glib::ustring extra = row[m_Columns.m_col_extra];

      //Some arbitrary logic just to show that this is where you can do such things:

      //Transform the value, deciding how to represent it as text:
      if(extra.empty())
        m_cell.property_text() = "(none)";
      else
        m_cell.property_text() = "-" + extra + "-";

      //Change other cell renderer properties too:
      m_cell.property_foreground() = (extra == "yadda" ? "red" : "green");
    }

    void ExampleWindow::on_combo_changed()
    {
      const auto iter = m_Combo.get_active();
      if(iter)
      {
        const auto row = *iter;
        if(row)
        {
          //Get the data for the selected row, using our knowledge of the tree
          //model:
          int id = row[m_Columns.m_col_id];
          Glib::ustring name = row[m_Columns.m_col_name];

          std::cout << " ID=" << id << ", name=" << name << std::endl;
        }
      }
      else
        std::cout << "invalid iter" << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Exemplo de texto simples

ComboBoxText

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm/window.h>
    #include <gtkmm/comboboxtext.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_combo_changed();

      //Child widgets:
      Gtk::ComboBoxText m_Combo;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    {
      set_title("ComboBoxText example");

      //Fill the combo:
      m_Combo.append("something");
      m_Combo.append("something else");
      m_Combo.append("something or other");
      m_Combo.set_active(1);

      set_child(m_Combo);

      //Connect signal handler:
      m_Combo.signal_changed().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_combo_changed) );
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_combo_changed()
    {
      Glib::ustring text = m_Combo.get_active_text();
      if(!(text.empty()))
        std::cout << "Combo changed: " << text << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### ComboBox com uma entrada

A ComboBox may contain an Entry widget for entering of arbitrary text, by specifying `true` for the constructor's `has_entry` parameter.

#### A coluna de texto

So that the Entry can interact with the drop-down list of choices, you must specify which of your model columns is the text column, with set_entry_text_column(). For instance:

    m_combo.set_entry_text_column(m_columns.m_col_name);

When you select a choice from the drop-down menu, the value from this column will be placed in the Entry.

#### Entrada

Because the user may enter arbitrary text, an active model row isn't enough to tell us what text the user has entered. Therefore, you should retrieve the Entry widget with the ComboBox::get_entry() method and call get_text() on that.

#### Respondendo as mudanças

When the user enters arbitrary text, it may not be enough to connect to the `changed` signal, which is emitted for every typed character. It is not emitted when the user presses the Enter key. Pressing the Enter key or moving the keyboard focus to another widget may signal that the user has finished entering text. To be notified of these events, connect to the Entry's `activate` signal (available since gtkmm 4.8), and add a Gtk::EventControllerFocus and connect to its `leave` signal, like so

    auto entry = m_Combo.get_entry();
    if (entry)
    {
      // Alternatively you can connect to m_Combo.signal_changed().
      entry->signal_changed().connect(sigc::mem_fun(*this,
        &ExampleWindow::on_entry_changed));
      entry->signal_activate().connect(sigc::mem_fun(*this,
        &ExampleWindow::on_entry_activate));
      // The Entry shall receive focus-leave events.
      auto controller = Gtk::EventControllerFocus::create();
      m_ConnectionFocusLeave = controller->signal_leave().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_entry_focus_leave));
      entry->add_controller(controller);
    }

The `changed` signals of ComboBox and Entry are both emitted for every change. It doesn't matter which one you connect to. But the EventControllerFocus must be added to the Entry.

#### Exemplo completo

Caixa de combinação com entrada

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm/window.h>
    #include <gtkmm/combobox.h>
    #include <gtkmm/liststore.h>
    #include <gtkmm/version.h>

    #define HAS_SIGNAL_ACTIVATE GTKMM_CHECK_VERSION(4,7,1)

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_entry_changed();
    #if HAS_SIGNAL_ACTIVATE
      void on_entry_activate();
    #endif
      void on_entry_focus_leave();

      //Signal connection:
      sigc::connection m_ConnectionFocusLeave;

      //Tree model columns:
      class ModelColumns : public Gtk::TreeModel::ColumnRecord
      {
      public:

        ModelColumns()
        { add(m_col_id); add(m_col_name); }

        Gtk::TreeModelColumn<Glib::ustring> m_col_id; //The data to choose - this must be text.
        Gtk::TreeModelColumn<Glib::ustring> m_col_name;
      };

      ModelColumns m_Columns;

      //Child widgets:
      Gtk::ComboBox m_Combo;
      Glib::RefPtr<Gtk::ListStore> m_refTreeModel;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/eventcontrollerfocus.h>
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_Combo(true /* has_entry */)
    {
      set_title("ComboBox example");

      //Create the Tree model:
      //m_refTreeModel = Gtk::TreeStore::create(m_Columns);
      m_refTreeModel = Gtk::ListStore::create(m_Columns);
      m_Combo.set_model(m_refTreeModel);

      //Fill the ComboBox's Tree Model:
      auto row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = "1";
      row[m_Columns.m_col_name] = "Billy Bob";
      /*
      auto childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_Columns.m_col_id] = 11;
      childrow[m_Columns.m_col_name] = "Billy Bob Junior";

      childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_Columns.m_col_id] = 12;
      childrow[m_Columns.m_col_name] = "Sue Bob";
      */

      row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = "2";
      row[m_Columns.m_col_name] = "Joey Jojo";

      row = *(m_refTreeModel->append());
      row[m_Columns.m_col_id] = "3";
      row[m_Columns.m_col_name] = "Rob McRoberts";

      /*
      childrow = *(m_refTreeModel->append(row.children()));
      childrow[m_Columns.m_col_id] = 31;
      childrow[m_Columns.m_col_name] = "Xavier McRoberts";
      */

      //Add the model columns to the Combo (which is a kind of view),
      //rendering them in the default way:
      //This is automatically rendered when we use set_entry_text_column().
      //m_Combo.pack_start(m_Columns.m_col_id, Gtk::PackOptions::EXPAND_WIDGET);
      m_Combo.pack_start(m_Columns.m_col_name);

      m_Combo.set_entry_text_column(m_Columns.m_col_id);
      m_Combo.set_active(1);

      //Add the ComboBox to the window.
      set_child(m_Combo);

      //Connect signal handlers:
      auto entry = m_Combo.get_entry();
      if (entry)
      {
        // Alternatively you can connect to m_Combo.signal_changed().
        entry->signal_changed().connect(sigc::mem_fun(*this,
          &ExampleWindow::on_entry_changed));
    #if HAS_SIGNAL_ACTIVATE
        entry->signal_activate().connect(sigc::mem_fun(*this,
          &ExampleWindow::on_entry_activate));
    #endif
        // The Entry shall receive focus-leave events.
        auto controller = Gtk::EventControllerFocus::create();
        m_ConnectionFocusLeave = controller->signal_leave().connect(
          sigc::mem_fun(*this, &ExampleWindow::on_entry_focus_leave));
        entry->add_controller(controller);
      }
      else
        std::cout << "No Entry ???" << std::endl;
    }

    ExampleWindow::~ExampleWindow()
    {
      // The focus-leave signal may be emitted while m_Combo is being destructed.
      // The signal handler can generate critical messages, if it's called when
      // m_Combo has been partly destructed.
      m_ConnectionFocusLeave.disconnect();
    }

    void ExampleWindow::on_entry_changed()
    {
      auto entry = m_Combo.get_entry();
      if (entry)
      {
        std::cout << "on_entry_changed(): Row=" << m_Combo.get_active_row_number()
          << ", ID=" << entry->get_text() << std::endl;
      }
    }

    #if HAS_SIGNAL_ACTIVATE
    void ExampleWindow::on_entry_activate()
    {
      auto entry = m_Combo.get_entry();
      if (entry)
      {
        std::cout << "on_entry_activate(): Row=" << m_Combo.get_active_row_number()
          << ", ID=" << entry->get_text() << std::endl;
      }
    }
    #endif

    void ExampleWindow::on_entry_focus_leave()
    {
      auto entry = m_Combo.get_entry();
      if (entry)
      {
        std::cout << "on_entry_focus_leave(): Row=" << m_Combo.get_active_row_number()
          << ", ID=" << entry->get_text() << std::endl;
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Exemplo de texto simples

ComboBoxText com uma entrada

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm/window.h>
    #include <gtkmm/comboboxtext.h>
    #include <gtkmm/version.h>

    #define HAS_SIGNAL_ACTIVATE GTKMM_CHECK_VERSION(4,7,1)

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_combo_changed();
    #if HAS_SIGNAL_ACTIVATE
      void on_entry_activate();
    #endif
      void on_entry_focus_leave();

      //Signal connection:
      sigc::connection m_ConnectionFocusLeave;

      //Child widgets:
      Gtk::ComboBoxText m_Combo;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/eventcontrollerfocus.h>
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_Combo(true /* has_entry */)
    {
      set_title("ComboBoxText example");

      //Fill the combo:
      m_Combo.append("something");
      m_Combo.append("something else");
      m_Combo.append("something or other");
      m_Combo.set_active(0);

      set_child(m_Combo);

      //Connect signal handlers:
      auto entry = m_Combo.get_entry();
      // Alternatively you can connect to entry->signal_changed().
      m_Combo.signal_changed().connect(sigc::mem_fun(*this,
        &ExampleWindow::on_combo_changed) );

      if (entry)
      {
    #if HAS_SIGNAL_ACTIVATE
        entry->signal_activate().connect(sigc::mem_fun(*this,
          &ExampleWindow::on_entry_activate));
    #endif
        // The Entry shall receive focus-leave events.
        auto controller = Gtk::EventControllerFocus::create();
        m_ConnectionFocusLeave = controller->signal_leave().connect(
          sigc::mem_fun(*this, &ExampleWindow::on_entry_focus_leave));
        entry->add_controller(controller);
      }
      else
        std::cout << "No Entry ???" << std::endl;

      m_Combo.property_has_frame() = false;
    }

    ExampleWindow::~ExampleWindow()
    {
      // The focus-leave signal may be emitted while m_Combo is being destructed.
      // The signal handler can generate critical messages, if it's called when
      // m_Combo has been partly destructed.
      m_ConnectionFocusLeave.disconnect();
    }

    void ExampleWindow::on_combo_changed()
    {
      std::cout << "on_combo_changed(): Row=" << m_Combo.get_active_row_number()
        << ", Text=" << m_Combo.get_active_text() << std::endl;
    }

    #if HAS_SIGNAL_ACTIVATE
    void ExampleWindow::on_entry_activate()
    {
      std::cout << "on_entry_activate(): Row=" << m_Combo.get_active_row_number()
        << ", Text=" << m_Combo.get_active_text() << std::endl;
    }
    #endif

    void ExampleWindow::on_entry_focus_leave()
    {
      std::cout << "on_entry_focus_leave(): Row=" << m_Combo.get_active_row_number()
        << ", Text=" << m_Combo.get_active_text() << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

## TextView

The TextView widget can be used to display and edit large amounts of formatted text. Like the TreeView, it has a model/view design. In this case the TextBuffer is the model.

### O Buffer

Gtk::TextBuffer is a model containing the data for the Gtk::TextView, like the Gtk::TreeModel used by Gtk::TreeView. This allows two or more Gtk::TextViews to share the same TextBuffer, and allows those TextBuffers to be displayed slightly differently. Or you could maintain several Gtk::TextBuffers and choose to display each one at different times in the same Gtk::TextView widget.

The TextView creates its own default TextBuffer, which you can access via the get_buffer() method.

Reference

#### Iterators

A Gtk::TextBuffer::iterator and a Gtk::TextBuffer::const_iterator represent a position between two characters in the text buffer. Whenever the buffer is modified in a way that affects the number of characters in the buffer, all outstanding iterators become invalid. Because of this, iterators can't be used to preserve positions across buffer modifications. To preserve a position, use Gtk::TextBuffer::Mark.

Reference

#### Etiquetas e formatação

##### Etiquetas

To specify that some text in the buffer should have specific formatting, you must define a tag to hold that formatting information, and then apply that tag to the region of text. For instance, to define the tag and its properties:

    auto refTagMatch = Gtk::TextBuffer::Tag::create();
    refTagMatch->property_background() = "orange";

You can specify a name for the Tag when using the create() method, but it is not necessary.

The Tag class has many other properties.

Reference

##### TagTable

Each Gtk::TextBuffer uses a Gtk::TextBuffer::TagTable, which contains the Tags for that buffer. 2 or more TextBuffers may share the same TagTable. When you create Tags you should add them to the TagTable. For instance:

    auto refTagTable = Gtk::TextBuffer::TagTable::create();
    refTagTable->add(refTagMatch);
    //Hopefully a future version of gtkmm will have a set_tag_table() method,
    //for use after creation of the buffer.
    auto refBuffer = Gtk::TextBuffer::create(refTagTable);

You can also use get_tag_table() to get, and maybe modify, the TextBuffer's default TagTable instead of creating one explicitly.

Reference

##### Aplicando etiquetas

If you have created a Tag and added it to the TagTable, you may apply that tag to part of the TextBuffer so that some of the text is displayed with that formatting. You define the start and end of the range of text by specifying Gtk::TextBuffer::iterators. For instance:

    refBuffer->apply_tag(refTagMatch, iterRangeStart, iterRangeStop);

Or you could specify the tag when first inserting the text:

    refBuffer->insert_with_tag(iter, "Some text", refTagMatch);

You can apply more than one Tag to the same text, by using apply_tag() more than once, or by using insert_with_tags(). The Tags might specify different values for the same properties, but you can resolve these conflicts by using Tag::set_priority().

#### Marcas

TextBuffer iterators are generally invalidated when the text changes, but you can use a Gtk::TextBuffer::Mark to remember a position in these situations. For instance,

    auto refMark = refBuffer->create_mark(iter);

You can then use the get_iter() method later to create an iterator for the Mark's new position.

There are two built-in Marks - `insert` and `selection_bound`, which you can access with TextBuffer's get_insert() and get_selection_bound() methods.

Reference

#### Visualização

As mentioned above, each TextView has a TextBuffer, and one or more TextViews can share the same TextBuffer.

Like the TreeView, you should probably put your TextView inside a ScrolledWindow to allow the user to see and move around the whole text area with scrollbars.

Reference

##### Formatação padrão

TextView has various methods which allow you to change the presentation of the buffer for this particular view. Some of these may be overridden by the Gtk::TextTags in the buffer, if they specify the same things. For instance, set_left_margin(), set_right_margin(), set_indent(), etc.

##### Deslocamento

Gtk::TextView has various scroll_to() methods. These allow you to ensure that a particular part of the text buffer is visible. For instance, your application's Find feature might use Gtk::TextView::scroll_to() to show the found text.

### Widgets and ChildAnchors

You can embed widgets, such as Gtk::Buttons, in the text. Each such child widget needs a ChildAnchor. ChildAnchors are associated with iterators. For instance, to create a child anchor at a particular position, use Gtk::TextBuffer::create_child_anchor():

    auto refAnchor = refBuffer->create_child_anchor(iter);

Then, to add a widget at that position, use Gtk::TextView::add_child_at_anchor():

    m_TextView.add_child_at_anchor(m_Button, refAnchor);

Reference

### Examples

#### Exemplo simples

TextView

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:

      void fill_buffers();

      //Signal handlers:
      void on_button_quit();
      void on_button_buffer1();
      void on_button_buffer2();

      //Child widgets:
      Gtk::Box m_VBox;

      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::TextView m_TextView;

      Glib::RefPtr<Gtk::TextBuffer> m_refTextBuffer1, m_refTextBuffer2;

      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit, m_Button_Buffer1, m_Button_Buffer2;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Quit("_Quit", true),
      m_Button_Buffer1("Use buffer 1"),
      m_Button_Buffer2("Use buffer 2")
    {
      set_title("Gtk::TextView example");
      set_default_size(400, 200);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      //Add the TreeView, inside a ScrolledWindow, with the button underneath:
      m_ScrolledWindow.set_child(m_TextView);

      //Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);

      //append buttons:
      m_VBox.append(m_ButtonBox);

      m_Button_Buffer1.set_hexpand(true);
      m_Button_Buffer1.set_halign(Gtk::Align::END);
      m_ButtonBox.append(m_Button_Buffer1);
      m_ButtonBox.append(m_Button_Buffer2);
      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(5);
      m_ButtonBox.set_spacing(5);

      //Connect signals:
      m_Button_Quit.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_quit) );
      m_Button_Buffer1.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_buffer1) );
      m_Button_Buffer2.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_buffer2) );

      fill_buffers();
      on_button_buffer1();
    }

    void ExampleWindow::fill_buffers()
    {
      m_refTextBuffer1 = Gtk::TextBuffer::create();
      m_refTextBuffer1->set_text("This is the text from TextBuffer #1.");

      m_refTextBuffer2 = Gtk::TextBuffer::create();
      m_refTextBuffer2->set_text(
              "This is some alternative text, from TextBuffer #2.");

    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void ExampleWindow::on_button_buffer1()
    {
      m_TextView.set_buffer(m_refTextBuffer1);
    }

    void ExampleWindow::on_button_buffer2()
    {
      m_TextView.set_buffer(m_refTextBuffer2);
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Other Examples

The example in the Internationalization and Localization chapter uses TextView.

There is a more complicated example among gtkmm's demo programs.

## Menus e barras de ferramentas

There are specific APIs for menus and toolbars, but you should usually deal with them together, creating Gio::SimpleActions that you can refer to in both menus and toolbars. In this way you can handle activation of the action instead of responding to the menu and toolbar items separately. And you can enable or disable both the menu and toolbar item via the action. Gtk::Builder can create menus and toolbars.

This involves the use of the Gio::SimpleActionGroup, Gio::SimpleAction and Gtk::Builder classes, all of which should be instantiated via their create() methods, which return RefPtrs.

### Ações

First create the Gio::SimpleActions and add them to a Gio::SimpleActionGroup, with Gio::ActionMap::add_action(). (Gio::ActionMap is a base class of Gio::SimpleActionGroup.) Then add the action group to your window with Gtk::Widget::insert_action_group().

The arguments to add_action() specify the action's name, which is used in the menu items and toolbar buttons. You can also specify a signal handler when calling add_action(). This signal handler will be called when the action is activated via either a menu item or a toolbar button.

Por exemplo:

    m_refActionGroup = Gio::SimpleActionGroup::create();

    m_refActionGroup->add_action("new", sigc::mem_fun(*this, &ExampleWindow::on_action_file_new));
    m_refActionGroup->add_action("open", sigc::mem_fun(*this, &ExampleWindow::on_action_file_open));
    m_refActionGroup->add_action("quit", sigc::mem_fun(*this, &ExampleWindow::on_action_file_quit));

    insert_action_group("example", m_refActionGroup);

If you use an Gtk::ApplicationWindow, you don't have to create your own action group. Gio::ActionGroup and Gio::ActionMap are base classes of Gtk::ApplicationWindow.

### Menubar and Toolbar

Next you should create a Gtk::Builder. At this point is also a good idea to tell the application to respond to keyboard shortcuts, by using Gtk::Application::set_accel_for_action().

Por exemplo,

    m_refBuilder = Gtk::Builder::create();

    app->set_accel_for_action("example.new", "<Primary>n");
    app->set_accel_for_action("example.quit", "<Primary>q");
    app->set_accel_for_action("example.copy", "<Primary>c");
    app->set_accel_for_action("example.paste", "<Primary>v");

Then, you can define the actual visible layout of the menus and toolbars, and add the UI layout to the Builder. This "ui string" uses an XML format, in which you should mention the names of the actions that you have already created. For instance:

    Glib::ustring ui_info =
      "<interface>"
      "  <menu id='menubar'>"
      "    <submenu>"
      "      <attribute name='label' translatable='yes'>_File</attribute>"
      "      <section>"
      "        <item>"
      "          <attribute name='label' translatable='yes'>_New</attribute>"
      "          <attribute name='action'>example.new</attribute>"
      "        </item>"
      "      </section>"
      "      <section>"
      "        <item>"
      "          <attribute name='label' translatable='yes'>_Quit</attribute>"
      "          <attribute name='action'>example.quit</attribute>"
      "        </item>"
      "      </section>"
      "    </submenu>"
      "    <submenu>"
      "      <attribute name='label' translatable='yes'>_Edit</attribute>"
      "      <item>"
      "        <attribute name='label' translatable='yes'>_Copy</attribute>"
      "        <attribute name='action'>example.copy</attribute>"
      "      </item>"
      "      <item>"
      "        <attribute name='label' translatable='yes'>_Paste</attribute>"
      "        <attribute name='action'>example.paste</attribute>"
      "      </item>"
      "    </submenu>"
      "  </menu>"
      "</interface>";

    m_refBuilder->add_from_string(ui_info);
    m_refBuilder->add_from_resource("/toolbar/toolbar.ui");

This is where we specify the names of the menu items as they will be seen by users in the menu. Therefore, this is where you should make strings translatable, by adding `translatable='yes'`.

To instantiate a Gtk::PopoverMenuBar and toolbar (a horizontal Gtk::Box) which you can actually show, you should use the Builder::get_object() and Builder::get_widget() methods, and then add the widgets to a container. For instance:

    auto gmenu = m_refBuilder->get_object<Gio::Menu>("menubar");
    auto pMenuBar = Gtk::make_managed<Gtk::PopoverMenuBar>(gmenu);
    m_Box.append(*pMenuBar);

    auto toolbar = m_refBuilder->get_widget<Gtk::Box>("toolbar");
    m_Box.append(*toolbar);

### Menus popup

Menus are normally just added to a window, but they can also be displayed temporarily as the result of a mouse button click. For instance, a context menu might be displayed when the user clicks their right mouse button.

Por exemplo:

    Glib::ustring ui_info =
      "<interface>"
      "  <menu id='menu-examplepopup'>"
      "    <section>"
      "      <item>"
      "        <attribute name='label' translatable='yes'>Edit</attribute>"
      "        <attribute name='action'>examplepopup.edit</attribute>"
      "      </item>"
      "      <item>"
      "        <attribute name='label' translatable='yes'>Process</attribute>"
      "        <attribute name='action'>examplepopup.process</attribute>"
      "      </item>"
      "      <item>"
      "        <attribute name='label' translatable='yes'>Remove</attribute>"
      "        <attribute name='action'>examplepopup.remove</attribute>"
      "      </item>"
      "    </section>"
      "  </menu>"
      "</interface>";

    m_refBuilder->add_from_string(ui_info);

    auto gmenu = m_refBuilder->get_object<Gio::Menu>("menu-examplepopup");
    m_MenuPopup.set_menu_model(gmenu);

To show the popup menu, use a Gtk::GestureClick and connect to its `pressed` signal. In the signal handler, use Gtk::PopoverMenu's popup() method. For instance:

    void ExampleWindow::on_label_pressed(int /* n_press */, double x, double y)
    {
      const Gdk::Rectangle rect(x, y, 1, 1);
      m_MenuPopup.set_pointing_to(rect);
      m_MenuPopup.popup();
    }

### Gio::Resource and glib-compile-resources

Applications and libraries often contain binary or textual data that is really part of the application, rather than user data. For instance Gtk::Builder `.ui` files, splashscreen images, Gio::Menu markup xml, CSS files, icons, etc. These are often shipped as files in `$datadir/appname`, or manually included as literal strings in the code.

The Gio::Resource API and the glib-compile-resources program provide a convenient and efficient alternative to this, which has some nice properties. You maintain the files as normal files, so it's easy to edit them, but during the build the files are combined into a binary bundle that is linked into the executable. This means that loading the resource files is efficient (as they are already in memory, shared with other instances) and simple (no need to check for things like I/O errors or locate the files in the filesystem). It also makes it easier to create relocatable applications.

Resource bundles are created by the glib-compile-resources program which takes an xml file that describes the bundle, and a set of files that the xml references. These are combined into a binary resource bundle.

Gio::Resource Reference

An example:

    <?xml version="1.0" encoding="UTF-8"?>
    <gresources>
      <gresource prefix="/toolbar">
        <file preprocess="xml-stripblanks">toolbar.ui</file>
        <file>rain.png</file>
      </gresource>
    </gresources>

This will create a resource bundle with the files

- `/toolbar/toolbar.ui`

- `/toolbar/rain.png`

You can then use glib-compile-resources to compile the xml to a binary bundle that you can load with Gio::Resource::create_from_file(). However, it's more common to use the --generate-source argument to create a C source file to link directly into your application. E.g.

    $ glib-compile-resources --target=resources.c --generate-source toolbar.gresource.xml

Once a Gio::Resource has been created and registered all the data in it can be accessed globally in the process by using API calls like Gio::Resource::open_stream_from_global_resources() to stream the data or Gio::Resource::lookup_data_in_global_resources() to get a direct pointer to the data. You can also use URIs like resource:///toolbar/rain.png with Gio::File to access the resource data.

Often you don't need a Gio::Resource instance, because resource data can be loaded with methods such as Gdk::Pixbuf::create_from_resource(), Gtk::Builder::add_from_resource() and Gtk::Image::set_from_resource().

### Examples

#### Application Menu and Main Menu example

This program contains an application menu, a menubar and a toolbar. Classes are derived from Gtk::Application and Gtk::ApplicationWindow.

App and Main Menu

Source Code

File: `exampleapplication.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPLICATION_H
    #define GTKMM_EXAMPLEAPPLICATION_H

    #include <gtkmm.h>

    class ExampleApplication : public Gtk::Application
    {
    protected:
      ExampleApplication();

    public:
      static Glib::RefPtr<ExampleApplication> create();

    protected:
      //Overrides of default signal handlers:
      void on_startup() override;
      void on_activate() override;

    private:
      void create_window();

      void on_menu_file_new_generic();
      void on_menu_file_quit();
      void on_menu_help_about();

      Glib::RefPtr<Gtk::Builder> m_refBuilder;
    };

    #endif /* GTKMM_EXAMPLEAPPLICATION_H */

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::ApplicationWindow
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_menu_others();

      void on_menu_choices(const Glib::ustring& parameter);
      void on_menu_choices_other(int parameter);
      void on_menu_toggle();

      //Child widgets:
      Gtk::Box m_Box;

      Glib::RefPtr<Gtk::Builder> m_refBuilder;

      //Two sets of choices:
      Glib::RefPtr<Gio::SimpleAction> m_refChoice;
      Glib::RefPtr<Gio::SimpleAction> m_refChoiceOther;

      Glib::RefPtr<Gio::SimpleAction> m_refToggle;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `exampleapplication.cc` (For use with gtkmm 4)

    #include "exampleapplication.h"
    #include "examplewindow.h"
    #include <iostream>

    ExampleApplication::ExampleApplication()
    : Gtk::Application("org.gtkmm.example.main_menu")
    {
      Glib::set_application_name("Main Menu Example");
    }

    Glib::RefPtr<ExampleApplication> ExampleApplication::create()
    {
      return Glib::make_refptr_for_instance<ExampleApplication>(new ExampleApplication());
    }

    void ExampleApplication::on_startup()
    {
      //Call the base class's implementation:
      Gtk::Application::on_startup();

      //Create actions for menus and toolbars.
      //We can use add_action() because Gtk::Application derives from Gio::ActionMap.

      //File|New sub menu:
      add_action("newstandard",
        sigc::mem_fun(*this, &ExampleApplication::on_menu_file_new_generic));

      add_action("newfoo",
        sigc::mem_fun(*this, &ExampleApplication::on_menu_file_new_generic));

      add_action("newgoo",
        sigc::mem_fun(*this, &ExampleApplication::on_menu_file_new_generic));

      //File menu:
      add_action("quit", sigc::mem_fun(*this, &ExampleApplication::on_menu_file_quit));

      //Help menu:
      add_action("about", sigc::mem_fun(*this, &ExampleApplication::on_menu_help_about));

      // Set accelerator keys:
      set_accel_for_action("app.newstandard", "<Primary>n");
      set_accel_for_action("app.quit", "<Primary>q");
      set_accel_for_action("win.copy", "<Primary>c");
      set_accel_for_action("win.paste", "<Primary>v");

      m_refBuilder = Gtk::Builder::create();

      //Layout the actions in a menubar and a menu:
      Glib::ustring ui_info =
        "<interface>"
        "  <!-- menubar -->"
        "  <menu id='menu-example'>"
        "    <submenu>"
        "      <attribute name='label' translatable='yes'>_File</attribute>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>New _Standard</attribute>"
        "          <attribute name='action'>app.newstandard</attribute>"
        "          <attribute name='accel'>&lt;Primary&gt;n</attribute>"
        "        </item>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>New _Foo</attribute>"
        "          <attribute name='action'>app.newfoo</attribute>"
        "        </item>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>New _Goo</attribute>"
        "          <attribute name='action'>app.newgoo</attribute>"
        "        </item>"
        "      </section>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_Quit</attribute>"
        "          <attribute name='action'>app.quit</attribute>"
        "          <attribute name='accel'>&lt;Primary&gt;q</attribute>"
        "        </item>"
        "      </section>"
        "    </submenu>"
        "    <submenu>"
        "      <attribute name='label' translatable='yes'>_Edit</attribute>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_Copy</attribute>"
        "          <attribute name='action'>win.copy</attribute>"
        "          <attribute name='accel'>&lt;Primary&gt;c</attribute>"
        "        </item>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_Paste</attribute>"
        "          <attribute name='action'>win.paste</attribute>"
        "          <attribute name='accel'>&lt;Primary&gt;v</attribute>"
        "        </item>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_Something</attribute>"
        "          <attribute name='action'>win.something</attribute>"
        "        </item>"
        "      </section>"
        "    </submenu>"
        "    <submenu>"
        "      <attribute name='label' translatable='yes'>_Choices</attribute>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>Choice _A</attribute>"
        "          <attribute name='action'>win.choice</attribute>"
        "          <attribute name='target'>a</attribute>"
        "        </item>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>Choice _B</attribute>"
        "          <attribute name='action'>win.choice</attribute>"
        "          <attribute name='target'>b</attribute>"
        "        </item>"
        "      </section>"
        "    </submenu>"
        "    <submenu>"
        "      <attribute name='label' translatable='yes'>_Other Choices</attribute>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>Choice 1</attribute>"
        "          <attribute name='action'>win.choiceother</attribute>"
        "          <attribute name='target' type='i'>1</attribute>"
        "        </item>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>Choice 2</attribute>"
        "          <attribute name='action'>win.choiceother</attribute>"
        "          <attribute name='target' type='i'>2</attribute>"
        "        </item>"
        "      </section>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>Some Toggle</attribute>"
        "          <attribute name='action'>win.sometoggle</attribute>"
        "        </item>"
        "      </section>"
        "    </submenu>"
        "    <submenu>"
        "      <attribute name='label' translatable='yes'>_Help</attribute>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_About Window</attribute>"
        "          <attribute name='action'>win.about</attribute>"
        "        </item>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_About App</attribute>"
        "          <attribute name='action'>app.about</attribute>"
        "        </item>"
        "      </section>"
        "    </submenu>"
        "  </menu>"
        "</interface>";

      try
      {
        m_refBuilder->add_from_string(ui_info);
      }
      catch (const Glib::Error& ex)
      {
        std::cerr << "Building menus failed: " << ex.what();
      }

      //Get the menubar and the app menu, and add them to the application:
      auto gmenu = m_refBuilder->get_object<Gio::Menu>("menu-example");
      if (!gmenu)
      {
        g_warning("GMenu not found");
      }
      else
      {
        set_menubar(gmenu);
      }
    }

    void ExampleApplication::on_activate()
    {
      //std::cout << "debug1: " << G_STRFUNC << std::endl;
      // The application has been started, so let's show a window.
      // A real application might want to reuse this window in on_open(),
      // when asked to open a file, if no changes have been made yet.
      create_window();
    }

    void ExampleApplication::create_window()
    {
      // Since gtkmm 4.8, a Gtk::Window can be managed. If managed and not created
      // by Gtk::Builder, it's deleted when its underlying C instance is destroyed.
      // The underlying C instance is destroyed when it's closed, unless
      // Gtk::Window::set_hide_on_close() has been called.
      auto win = Gtk::make_managed<ExampleWindow>();

      //Make sure that the application runs for as long this window is still open:
      add_window(*win);

      win->set_show_menubar();
      win->set_visible(true);
    }

    void ExampleApplication::on_menu_file_new_generic()
    {
      std::cout << "A File|New menu item was selected." << std::endl;
    }

    void ExampleApplication::on_menu_file_quit()
    {
      std::cout << G_STRFUNC << std::endl;
      quit(); // Not really necessary, when Gtk::Window::close() is called.

      // Gio::Application::quit() will make Gio::Application::run() return,
      // but it's a crude way of ending the program. The window is not removed
      // from the application. Neither the window's nor the application's
      // destructors will be called, because there will be remaining reference
      // counts in both of them. If we want the destructors to be called, we
      // must close the window.
      auto windows = get_windows();
      for (auto window : windows)
        window->close();
    }

    void ExampleApplication::on_menu_help_about()
    {
      std::cout << "Help|About App was selected." << std::endl;
    }

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : Gtk::ApplicationWindow(),
      m_Box(Gtk::Orientation::VERTICAL)
    {
      set_title("Main menu example");
      set_default_size(300, 100);

      // ExampleApplication displays the menubar. Other stuff, such as a toolbar,
      // is put into the box.
      set_child(m_Box);

      // Create actions for menus and toolbars.
      // We can use add_action() because Gtk::ApplicationWindow derives from Gio::ActionMap.
      // This Action Map uses a "win." prefix for the actions.
      // Therefore, for instance, "win.copy", is used in ExampleApplication::on_startup()
      // to layout the menu.

      //Edit menu:
      add_action("copy", sigc::mem_fun(*this, &ExampleWindow::on_menu_others));
      add_action("paste", sigc::mem_fun(*this, &ExampleWindow::on_menu_others));
      add_action("something", sigc::mem_fun(*this, &ExampleWindow::on_menu_others));

      //Choices menus, to demonstrate Radio items,
      //using our convenience methods for string and int radio values:
      m_refChoice = add_action_radio_string("choice",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_choices), "a");

      m_refChoiceOther = add_action_radio_integer("choiceother",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_choices_other), 1);

      m_refToggle = add_action_bool("sometoggle",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_toggle), false);

      //Help menu:
      add_action("about", sigc::mem_fun(*this, &ExampleWindow::on_menu_others));

      //Create the toolbar and add it to a container widget:

      m_refBuilder = Gtk::Builder::create();

      Glib::ustring ui_info =
        "<!-- Generated with glade 3.18.3 and then changed manually -->"
        "<interface>"
        "  <object class='GtkBox' id='toolbar'>"
        "    <property name='can_focus'>False</property>"
        "    <child>"
        "      <object class='GtkButton' id='toolbutton_new'>"
        "        <property name='can_focus'>False</property>"
        "        <property name='tooltip_text' translatable='yes'>New Standard</property>"
        "        <property name='action_name'>app.newstandard</property>"
        "        <property name='icon_name'>document-new</property>"
        "        <property name='hexpand'>False</property>"
        "        <property name='vexpand'>False</property>"
        "      </object>"
        "    </child>"
        "    <child>"
        "      <object class='GtkButton' id='toolbutton_quit'>"
        "        <property name='can_focus'>False</property>"
        "        <property name='tooltip_text' translatable='yes'>Quit</property>"
        "        <property name='action_name'>app.quit</property>"
        "        <property name='icon_name'>application-exit</property>"
        "        <property name='hexpand'>False</property>"
        "        <property name='vexpand'>False</property>"
        "      </object>"
        "    </child>"
        "  </object>"
        "</interface>";

      try
      {
        m_refBuilder->add_from_string(ui_info);
      }
      catch (const Glib::Error& ex)
      {
        std::cerr << "Building toolbar failed: " <<  ex.what();
      }

      auto toolbar = m_refBuilder->get_widget<Gtk::Box>("toolbar");
      if (!toolbar)
        g_warning("toolbar not found");
      else
        m_Box.append(*toolbar);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_menu_others()
    {
      std::cout << "A menu item was selected." << std::endl;
    }

    void ExampleWindow::on_menu_choices(const Glib::ustring& parameter)
    {
      //The radio action's state does not change automatically:
      m_refChoice->change_state(parameter);

      Glib::ustring message;
      if (parameter == "a")
        message = "Choice a was selected.";
      else
        message = "Choice b was selected.";

      std::cout << message << std::endl;
    }

    void ExampleWindow::on_menu_choices_other(int parameter)
    {
      //The radio action's state does not change automatically:
      m_refChoiceOther->change_state(parameter);

      Glib::ustring message;
      if (parameter == 1)
        message = "Choice 1 was selected.";
      else
        message = "Choice 2 was selected.";

      std::cout << message << std::endl;
    }

    void ExampleWindow::on_menu_toggle()
    {
      bool active = false;
      m_refToggle->get_state(active);

      //The toggle action's state does not change automatically:
      active = !active;
      m_refToggle->change_state(active);

      Glib::ustring message;
      if (active)
        message = "Toggle is active.";
      else
        message = "Toggle is not active.";

      std::cout << message << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "exampleapplication.h"

    int main(int argc, char* argv[])
    {
      auto application = ExampleApplication::create();

      // Start the application, showing the initial window,
      // and opening extra windows for any files that it is asked to open,
      // for instance as a command-line parameter.
      // run() will return when the last window has been closed by the user.
      const int status = application->run(argc, argv);
      return status;
    }

#### Exemplo de menu principal

This program contains a menubar and a toolbar. A class is derived from Gtk::Window.

Menu principal

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow(const Glib::RefPtr<Gtk::Application>& app);
      virtual ~ExampleWindow();

    private:
      //Signal handlers:
      //void on_action_file_new();
      void on_action_file_quit();
      void on_action_others();
      void on_action_toggle();

      //Child widgets:
      Gtk::Box m_Box;

      Glib::RefPtr<Gtk::Builder> m_refBuilder;
      Glib::RefPtr<Gio::SimpleActionGroup> m_refActionGroup;
      Glib::RefPtr<Gio::SimpleAction> m_refActionRain;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm.h>
    #include <iostream>

    ExampleWindow::ExampleWindow(const Glib::RefPtr<Gtk::Application>& app)
    : m_Box(Gtk::Orientation::VERTICAL)
    {
      set_title("main_menu example");
      set_default_size(200, 200);

      set_child(m_Box); //We can put a MenuBar at the top of the box and other stuff below it.

      //Define the actions:
      m_refActionGroup = Gio::SimpleActionGroup::create();

      // There are several ways of calling a function that takes a sigc::slot.
      // If the slot function is very short, it might be easy to skip the on_xxx()
      // method and put its contents directly in a lambda expression.
      m_refActionGroup->add_action("new",
        [] { std::cout << "A File|New menu item was selected.\n"; /* on_action_file_new() */});
      // With sigc::mem_fun() or (for non-member functions and static member functions)
      // sigc::ptr_fun(). The only way before C++11 introduced lambda expressions.
      m_refActionGroup->add_action("open",
        sigc::mem_fun(*this, &ExampleWindow::on_action_others) );

      // With a lambda expression. Does not disconnect automatically when ExampleWindow
      // is deleted, like sigc::mem_fun() does.
      m_refActionRain = m_refActionGroup->add_action_bool("rain",
        [this] { on_action_toggle(); }, false);

      m_refActionGroup->add_action("quit",
        sigc::mem_fun(*this, &ExampleWindow::on_action_file_quit) );

      // With a lambda expression and sigc::track_obj() or sigc::track_object().
      // Disconnects automatically like sigc::mem_fun().
    #if SIGCXX_MINOR_VERSION >= 4
      m_refActionGroup->add_action("cut",
        sigc::track_object([this] { on_action_others(); }, *this));
    #else
      m_refActionGroup->add_action("cut",
        sigc::track_obj([this] { on_action_others(); }, *this));
    #endif
      m_refActionGroup->add_action("copy",
        sigc::mem_fun(*this, &ExampleWindow::on_action_others) );
      m_refActionGroup->add_action("paste",
        sigc::mem_fun(*this, &ExampleWindow::on_action_others) );

      insert_action_group("example", m_refActionGroup);

      //Define how the actions are presented in the menus and toolbars:
      m_refBuilder = Gtk::Builder::create();

      //Layout the actions in a menubar and toolbar:
      const Glib::ustring ui_info =
        "<interface>"
        "  <menu id='menubar'>"
        "    <submenu>"
        "      <attribute name='label' translatable='yes'>_File</attribute>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_New</attribute>"
        "          <attribute name='action'>example.new</attribute>"
        "        </item>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_Open</attribute>"
        "          <attribute name='action'>example.open</attribute>"
        "        </item>"
        "      </section>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>Rain</attribute>"
        "          <attribute name='action'>example.rain</attribute>"
        "        </item>"
        "      </section>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_Quit</attribute>"
        "          <attribute name='action'>example.quit</attribute>"
        "        </item>"
        "      </section>"
        "    </submenu>"
        "    <submenu>"
        "      <attribute name='label' translatable='yes'>_Edit</attribute>"
        "      <item>"
        "        <attribute name='label' translatable='yes'>_Cut</attribute>"
        "        <attribute name='action'>example.cut</attribute>"
        "      </item>"
        "      <item>"
        "        <attribute name='label' translatable='yes'>_Copy</attribute>"
        "        <attribute name='action'>example.copy</attribute>"
        "      </item>"
        "      <item>"
        "        <attribute name='label' translatable='yes'>_Paste</attribute>"
        "        <attribute name='action'>example.paste</attribute>"
        "      </item>"
        "    </submenu>"
        "  </menu>"
        "</interface>";

      // Set accelerator keys:
      app->set_accel_for_action("example.new", "<Primary>n");
      app->set_accel_for_action("example.open", "<Primary>o");
      app->set_accel_for_action("example.quit", "<Primary>q");
      app->set_accel_for_action("example.cut", "<Primary>x");
      app->set_accel_for_action("example.copy", "<Primary>c");
      app->set_accel_for_action("example.paste", "<Primary>v");

      try
      {
        m_refBuilder->add_from_string(ui_info);
        m_refBuilder->add_from_resource("/toolbar/toolbar.ui");
      }
      catch(const Glib::Error& ex)
      {
        std::cerr << "Building menus and toolbar failed: " <<  ex.what();
      }

      //Get the menubar:
      auto gmenu = m_refBuilder->get_object<Gio::Menu>("menubar");
      if (!gmenu)
        g_warning("GMenu not found");
      else
      {
        auto pMenuBar = Gtk::make_managed<Gtk::PopoverMenuBar>(gmenu);

        //Add the PopoverMenuBar to the window:
        m_Box.append(*pMenuBar);
      }

      //Get the toolbar and add it to a container widget:
      auto toolbar = m_refBuilder->get_widget<Gtk::Box>("toolbar");
      if (!toolbar)
        g_warning("toolbar not found");
      else
        m_Box.append(*toolbar);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_action_file_quit()
    {
      close();
    }

    //void ExampleWindow::on_action_file_new()
    //{
    //   std::cout << "A File|New menu item was selected." << std::endl;
    //}

    void ExampleWindow::on_action_others()
    {
      std::cout << "A menu item was selected." << std::endl;
    }

    void ExampleWindow::on_action_toggle()
    {
      std::cout << "The toggle menu item was selected." << std::endl;

      bool active = false;
      m_refActionRain->get_state(active);

      //The toggle action's state does not change automatically:
      active = !active;
      m_refActionRain->change_state(active);

      Glib::ustring message;
      if(active)
        message = "Toggle is active.";
      else
        message = "Toggle is not active";

      std::cout << message << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include <gtkmm.h>
    #include "examplewindow.h"

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv, app);
    }

File: `toolbar.gresource.xml` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <gresources>
      <gresource prefix="/toolbar">
        <file preprocess="xml-stripblanks">toolbar.ui</file>
        <file>rain.png</file>
      </gresource>
    </gresources>

#### Exemplo de menu popup

Menu popup

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    #include <memory>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow(const Glib::RefPtr<Gtk::Application>& app);
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_label_pressed(int n_press, double x, double y);

      void on_menu_file_popup_generic();

      //Child widgets:
      Gtk::Box m_Box;
      Gtk::Label m_Label;
      Gtk::PopoverMenu m_MenuPopup;

      Glib::RefPtr<Gtk::Builder> m_refBuilder;
      Glib::RefPtr<Gtk::GestureClick> m_refGesture;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow(const Glib::RefPtr<Gtk::Application>& app)
    : m_Box(Gtk::Orientation::VERTICAL),
      m_Label("Right-click to see the popup menu.")
    {
      set_title("popup example");
      set_default_size(200, 200);

      set_child(m_Box);

      // Catch button_press events:
      m_Box.append(m_Label);
      m_Label.set_expand();
      m_refGesture = Gtk::GestureClick::create();
      m_refGesture->set_button(GDK_BUTTON_SECONDARY);
      m_refGesture->signal_pressed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_label_pressed));
      m_Label.add_controller(m_refGesture);

      //Create actions:
      auto refActionGroup = Gio::SimpleActionGroup::create();

      //File|New sub menu:
      //These menu actions would normally already exist for a main menu, because a
      //context menu should not normally contain menu items that are only available
      //via a context menu.

      refActionGroup->add_action("edit",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_popup_generic));

      refActionGroup->add_action("process",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_popup_generic));

      refActionGroup->add_action("remove",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_popup_generic));

      insert_action_group("examplepopup", refActionGroup);

      // Set accelerator keys:
      app->set_accel_for_action("examplepopup.edit", "<Primary>e");
      app->set_accel_for_action("examplepopup.process", "<Primary>p");
      app->set_accel_for_action("examplepopup.remove", "<Primary>r");

      m_refBuilder = Gtk::Builder::create();

      //Layout the actions in a menubar and toolbar:
      Glib::ustring ui_info =
        "<interface>"
        "  <menu id='menu-examplepopup'>"
        "    <section>"
        "      <item>"
        "        <attribute name='label' translatable='yes'>Edit</attribute>"
        "        <attribute name='action'>examplepopup.edit</attribute>"
        "      </item>"
        "      <item>"
        "        <attribute name='label' translatable='yes'>Process</attribute>"
        "        <attribute name='action'>examplepopup.process</attribute>"
        "      </item>"
        "      <item>"
        "        <attribute name='label' translatable='yes'>Remove</attribute>"
        "        <attribute name='action'>examplepopup.remove</attribute>"
        "      </item>"
        "    </section>"
        "  </menu>"
        "</interface>";

      try
      {
        m_refBuilder->add_from_string(ui_info);
      }
      catch(const Glib::Error& ex)
      {
        std::cerr << "building menus failed: " <<  ex.what();
      }

      //Get the menu:
      auto gmenu = m_refBuilder->get_object<Gio::Menu>("menu-examplepopup");
      if(!gmenu)
        g_warning("GMenu not found");

      m_MenuPopup.set_parent(m_Label);
      m_MenuPopup.set_menu_model(gmenu);
      m_MenuPopup.set_has_arrow(false);
    }

    ExampleWindow::~ExampleWindow()
    {
      m_MenuPopup.unparent();
    }

    void ExampleWindow::on_menu_file_popup_generic()
    {
       std::cout << "A popup menu item was selected." << std::endl;
    }

    void ExampleWindow::on_label_pressed(int /* n_press */, double x, double y)
    {
      const Gdk::Rectangle rect(x, y, 1, 1);
      m_MenuPopup.set_pointing_to(rect);
      m_MenuPopup.popup();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv, app);
    }

## Ajustes

gtkmm has various widgets that can be visually adjusted using the mouse or the keyboard, such as the Range widgets (described in the Range Widgets section). There are also a few widgets that display some adjustable part of a larger area, such as the Viewport widget. These widgets have Gtk::Adjustment objects that express this common part of their API.

So that applications can react to changes, for instance when a user moves a scrollbar, Gtk::Adjustment has a `value_changed` signal. You can then use the get_value() method to discover the new value.

### Criando um ajuste

The Gtk::Adjustment is created by its create() method which is as follows:

    Glib::RefPtr<Gtk::Adjustment> Gtk::Adjustment::create(
      double value,
      double lower,
      double upper,
      double step_increment = 1,
      double page_increment = 10,
      double page_size = 0);

The value argument is the initial value of the adjustment, usually corresponding to the topmost or leftmost position of an adjustable widget. The lower and upper arguments specify the possible range of values which the adjustment can hold. The step_increment argument specifies the smaller of the two increments by which the user can change the value, while the page_increment is the larger one. The page_size argument usually corresponds somehow to the visible area of a panning widget. The upper argument is used to represent the bottommost or rightmost coordinate in a panning widget's child.

### Usando ajustes o caminho fácil

Os widgets ajustáveis ​​podem ser grosseiramente divididos naqueles que usam e requerem unidades específicas para estes valores, e aqueles que tratá-los como números arbitrários.

The group which treats the values as arbitrary numbers includes the Range widgets (Scrollbar and Scale), the ScaleButton widget, and the SpinButton widget. These widgets are typically "adjusted" directly by the user with the mouse or keyboard. They will treat the lower and upper values of an adjustment as a range within which the user can manipulate the adjustment's value. By default, they will only modify the value of an adjustment.

The other group includes the Viewport widget and the ScrolledWindow widget. All of these widgets use pixel values for their adjustments. These are also typically adjusted indirectly using scrollbars. While all widgets which use adjustments can either create their own adjustments or use ones you supply, you'll generally want to let this particular category of widgets create its own adjustments.

If you share an adjustment object between a Scrollbar and a TextView widget, manipulating the scrollbar will automagically adjust the TextView widget. You can set it up like this:

    // creates its own adjustments
    Gtk::TextView textview;
    // uses the newly-created adjustment for the scrollbar as well
    Gtk::Scrollbar vscrollbar(textview.get_vadjustment(), Gtk::Orientation::VERTICAL);

### Ajustamento interno

OK, you say, that's nice, but what if I want to create my own handlers to respond when the user adjusts a Range widget or a SpinButton. To access the value of a Gtk::Adjustment, you can use the get_value() and set_value() methods:

As mentioned earlier, Gtk::Adjustment can emit signals. This is, of course, how updates happen automatically when you share an Adjustment object between a Scrollbar and another adjustable widget; all adjustable widgets connect signal handlers to their adjustment's `value_changed` signal, as can your program.

So, for example, if you have a Scale widget, and you want to change the rotation of a picture whenever its value changes, you would create a signal handler like this:

    void cb_rotate_picture(MyPicture* picture)
    {
      picture->set_rotation(adj->get_value());
    ...

and connect it to the scale widget's adjustment like this:

    adj->signal_value_changed().connect(sigc::bind<MyPicture*>(sigc::mem_fun(*this,
        &cb_rotate_picture), picture));

What if a widget reconfigures the upper or lower fields of its Adjustment, such as when a user adds more text to a text widget? In this case, it emits the `changed` signal.

Range widgets typically connect a handler to this signal, which changes their appearance to reflect the change - for example, the size of the slider in a scrollbar will grow or shrink in inverse proportion to the difference between the lower and upper values of its Adjustment.

You probably won't ever need to attach a handler to this signal, unless you're writing a new type of range widget.

    adjustment->signal_changed();

## Caixas de diálogo

Gtk::Dialog and the classes derived from it, are deprecated since gtkmm 4.10. They can still be used in gtkmm4 applications, provided GTKMM_DISABLE_DEPRECATED and GDKMM_DISABLE_DEPRECATED are not defined. Some of the dialog classes are replaced by classes that are available since gtkmm 4.10.

The examples in this chapter use classes that are available since gtkmm 4.10. Similar examples with the deprecated classes are available in the gtkmm-4-0 branch in the git repository.

Dialogs are used as secondary windows, to provide specific information or to ask questions. Gtk::Dialog windows contain a few pre-packed widgets to ensure consistency, and a `response` signal which is emitted when the user dismisses the dialog.

There are several derived Dialog classes which you might find useful. Gtk::MessageDialog is used for most simple notifications. But at other times you might need to derive your own dialog class to provide more complex functionality.

To pack widgets into a custom dialog, you should pack them into the Gtk::Box, available via get_content_area(). To just add a Button to the bottom of the Dialog, you could use the add_button() method.

The `response` signal handler receives an `int`. This may be a value from the Gtk::ResponseType if the user closed the dialog by clicking a standard button, or it could be the custom response value that you specified when using add_button().

To show the dialog, call set_visible(true). If the same dialog instance will be shown several times, you must also call set_hide_on_close(), or else the dialog will be destroyed when it's closed. Connect to the `response` signal, if you want to know which button was pressed. The `response` signal handler is also where you should hide the dialog.

Reference

### AlertDialog and MessageDialog

MessageDialog (deprecated since gtkmm 4.10) and AlertDialog (available since gtkmm 4.10) are convenience classes, used to create simple, standard message dialogs, with a message and buttons for user response.

AlertDialog Reference

MessageDialog Reference

#### Exemplo

AlertDialog

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_button_info_clicked();
      void on_button_question_clicked();
      void on_question_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result);

      //Child widgets:
      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Info;
      Gtk::Button m_Button_Question;

      Glib::RefPtr<Gtk::AlertDialog> m_pDialog;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/messagedialog.h>
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_ButtonBox(Gtk::Orientation::VERTICAL),
      m_Button_Info("Show Info AlertDialog"),
      m_Button_Question("Show Question AlertDialog")
    {
      set_title("Gtk::AlertDialog example");

      set_child(m_ButtonBox);

      m_ButtonBox.append(m_Button_Info);
      m_Button_Info.set_expand(true);
      m_Button_Info.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_info_clicked) );

      m_ButtonBox.append(m_Button_Question);
      m_Button_Question.set_expand(true);
      m_Button_Question.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_question_clicked) );
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_info_clicked()
    {
      if (!m_pDialog)
        m_pDialog = Gtk::AlertDialog::create();
      else
      {
        // Reset values that may have been set by on_button_question_clicked().
        m_pDialog->set_buttons({});
        m_pDialog->set_default_button(-1);
        m_pDialog->set_cancel_button(-1);
      }

      m_pDialog->set_message("This is an INFO AlertDialog.");
      m_pDialog->set_detail("And this is the secondary text that explains things.");
      m_pDialog->show(*this);
    }

    void ExampleWindow::on_button_question_clicked()
    {
      if (!m_pDialog)
        m_pDialog = Gtk::AlertDialog::create();
      m_pDialog->set_message("This is a QUESTION AlertDialog.");
      m_pDialog->set_detail("And this is the secondary text that explains things.");
      m_pDialog->set_buttons({"Cancel", "Retry", "OK"});
      m_pDialog->set_default_button(2); // OK button or Return key
      m_pDialog->set_cancel_button(0); // Cancel button or Escape key
      m_pDialog->choose(*this,
        sigc::mem_fun(*this, &ExampleWindow::on_question_dialog_finish));
    }

    void ExampleWindow::on_question_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result)
    {
      try
      {
        const int response_id = m_pDialog->choose_finish(result);
        switch (response_id)
        {
        case 0:
          std::cout << "Cancel clicked." << std::endl;
          break;
        case 1:
          std::cout << "Retry clicked." << std::endl;
          break;
        case 2:
          std::cout << "OK clicked." << std::endl;
          break;
        default:
          std::cout << "Unexpected response: " << response_id << std::endl;
          break;
        }
      }
      catch (const Gtk::DialogError& err)
      {
        // Can be thrown by m_pDialog->choose_finish(result).
        std::cout << "DialogError, " << err.what() << std::endl;
      }
      catch (const Glib::Error& err)
      {
        std::cout << "Unexpected exception. " << err.what() << std::endl;
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### FileDialog and FileChooserDialog

The FileChooserDialog (deprecated since gtkmm 4.10) and FileDialog (available since gtkmm 4.10) are suitable for use with "Open" or "Save" menu items.

Most of the useful member methods for FileChooserDialog are actually in the Gtk::FileChooser base class.

FileDialog Reference

FileChooserDialog Reference

#### Exemplo

FileDialog

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_button_file_clicked();
      void on_button_folder_clicked();
      void on_file_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result,
        const Glib::RefPtr<Gtk::FileDialog>& dialog);
      void on_folder_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result,
        const Glib::RefPtr<Gtk::FileDialog>& dialog);

      //Child widgets:
      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_File;
      Gtk::Button m_Button_Folder;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_ButtonBox(Gtk::Orientation::VERTICAL),
      m_Button_File("Choose File"),
      m_Button_Folder("Choose Folder")
    {
      set_title("Gtk::FileDialog example");

      set_child(m_ButtonBox);

      m_ButtonBox.append(m_Button_File);
      m_Button_File.set_expand(true);
      m_Button_File.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_file_clicked) );

      m_ButtonBox.append(m_Button_Folder);
      m_Button_Folder.set_expand(true);
      m_Button_Folder.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_folder_clicked) );
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_file_clicked()
    {
      auto dialog = Gtk::FileDialog::create();

      // Add filters, so that only certain file types can be selected:
      auto filters = Gio::ListStore<Gtk::FileFilter>::create();

      auto filter_text = Gtk::FileFilter::create();
      filter_text->set_name("Text files");
      filter_text->add_mime_type("text/plain");
      filters->append(filter_text);

      auto filter_cpp = Gtk::FileFilter::create();
      filter_cpp->set_name("C/C++ files");
      filter_cpp->add_mime_type("text/x-c");
      filter_cpp->add_mime_type("text/x-c++");
      filter_cpp->add_mime_type("text/x-c-header");
      filters->append(filter_cpp);

      auto filter_any = Gtk::FileFilter::create();
      filter_any->set_name("Any files");
      filter_any->add_pattern("*");
      filters->append(filter_any);

      dialog->set_filters(filters);

      // Show the dialog and wait for a user response:
      dialog->open(sigc::bind(sigc::mem_fun(
        *this, &ExampleWindow::on_file_dialog_finish), dialog));
    }

    void ExampleWindow::on_file_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result,
      const Glib::RefPtr<Gtk::FileDialog>& dialog)
    {
      // Handle the response:
      try
      {
        auto file = dialog->open_finish(result);

        // Notice that this is a std::string, not a Glib::ustring.
        auto filename = file->get_path();
        std::cout << "File selected: " <<  filename << std::endl;
      }
      catch (const Gtk::DialogError& err)
      {
        // Can be thrown by dialog->open_finish(result).
        std::cout << "No file selected. " << err.what() << std::endl;
      }
      catch (const Glib::Error& err)
      {
        std::cout << "Unexpected exception. " << err.what() << std::endl;
      }
    }

    void ExampleWindow::on_button_folder_clicked()
    {
      auto dialog = Gtk::FileDialog::create();

      // Show the dialog and wait for a user response:
      dialog->select_folder(sigc::bind(sigc::mem_fun(
        *this, &ExampleWindow::on_folder_dialog_finish), dialog));
    }

    void ExampleWindow::on_folder_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result,
      const Glib::RefPtr<Gtk::FileDialog>& dialog)
    {
      // Handle the response:
      try
      {
        auto folder = dialog->select_folder_finish(result);
        std::cout << "Folder selected: " << folder->get_path() << std::endl;
      }
      catch (const Gtk::DialogError& err)
      {
        // Can be thrown by dialog->select_folder_finish(result).
        std::cout << "No folder selected. " << err.what() << std::endl;
      }
      catch (const Glib::Error& err)
      {
        std::cout << "Unexpected exception. " << err.what() << std::endl;
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### ColorDialog and ColorChooserDialog

The ColorChooserDialog (deprecated since gtkmm 4.10) and ColorDialog (available since gtkmm 4.10) allow the user to choose a color. The ColorButton (deprecated since gtkmm 4.10) and ColorDialogButton (available since gtkmm 4.10) open a color selection dialog when it is clicked.

ColorDialog Reference

ColorChooserDialog Reference

#### Exemplo

ColorDialog

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_color_button_color_set();
      void on_button_dialog_clicked();
      void on_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result);

      //Draw function:
      void on_drawing_area_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);

      //Child widgets:
      Gtk::Box m_VBox;
      Gtk::ColorDialogButton m_ColorDialogButton;
      Gtk::Button m_Button_Dialog;
      Gtk::DrawingArea m_DrawingArea; //To show the color.

      Glib::RefPtr<Gtk::ColorDialog> m_pDialog;
      Gdk::RGBA m_Color;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL, 5),
      m_Button_Dialog("Choose Color")
    {
      set_title("Gtk::ColorDialog example");
      set_default_size(200, 200);

      m_pDialog = Gtk::ColorDialog::create();
      m_ColorDialogButton.set_dialog(m_pDialog);

      set_child(m_VBox);

      m_VBox.append(m_ColorDialogButton);
      m_ColorDialogButton.property_rgba().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_color_button_color_set));

      m_VBox.append(m_Button_Dialog);
      m_Button_Dialog.signal_clicked().connect(sigc::mem_fun(*this,
        &ExampleWindow::on_button_dialog_clicked) );

      //Set start color:
      m_Color.set_red(0.0);
      m_Color.set_green(0.0);
      m_Color.set_blue(1.0);
      m_Color.set_alpha(1.0); //opaque
      m_ColorDialogButton.set_rgba(m_Color);

      m_VBox.append(m_DrawingArea);
      m_DrawingArea.set_expand(true);
      m_DrawingArea.set_draw_func(sigc::mem_fun(*this, &ExampleWindow::on_drawing_area_draw));
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_color_button_color_set()
    {
      //Store the chosen color:
      m_Color = m_ColorDialogButton.get_rgba();
      m_DrawingArea.queue_draw();
    }

    void ExampleWindow::on_button_dialog_clicked()
    {
      m_pDialog->choose_rgba(*this, m_Color,
        sigc::mem_fun(*this, &ExampleWindow::on_dialog_finish));
    }

    void ExampleWindow::on_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result)
    {
      try
      {
        // If this call changes the color, it will trigger a call to
        // on_color_button_color_set().
        m_ColorDialogButton.set_rgba(m_pDialog->choose_rgba_finish(result));

        // This is what you should do if m_ColorDialogButton and
        // on_color_button_color_set() did not exist:
        //m_Color = m_pDialog->choose_rgba_finish(result);
        //m_DrawingArea.queue_draw();
      }
      catch (const Gtk::DialogError& err)
      {
        // Can be thrown by m_pDialog->choose_rgba_finish(result).
        std::cout << "No color selected. " << err.what() << std::endl;
      }
      catch (const Glib::Error& err)
      {
        std::cout << "Unexpected exception. " << err.what() << std::endl;
      }
    }

    void ExampleWindow::on_drawing_area_draw(const Cairo::RefPtr<Cairo::Context>& cr, int, int)
    {
      Gdk::Cairo::set_source_rgba(cr, m_Color);
      cr->paint();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### FontDialog and FontChooserDialog

The FontChooserDialog (deprecated since gtkmm 4.10) and FontDialog (available since gtkmm 4.10) allow the user to choose a font. The FontButton (deprecated since gtkmm 4.10) and FontDialogButton (available since gtkmm 4.10) open a font chooser dialog when it is clicked.

FontDialog Reference

FontChooserDialog Reference

#### Exemplo

FontDialog

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_font_button_font_set();
      void on_button_dialog_clicked();
      void on_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result);

      //Child widgets:
      Gtk::Box m_ButtonBox;
      Gtk::FontDialogButton m_FontDialogButton;
      Gtk::Button m_Button_Dialog;

      Glib::RefPtr<Gtk::FontDialog> m_pDialog;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_ButtonBox(Gtk::Orientation::VERTICAL),
      m_Button_Dialog("Choose Font")
    {
      set_title("Gtk::FontDialog example");

      set_child(m_ButtonBox);

      m_pDialog = Gtk::FontDialog::create();

      m_ButtonBox.append(m_FontDialogButton);
      m_FontDialogButton.set_dialog(m_pDialog);
      m_FontDialogButton.set_font_desc(Pango::FontDescription("Sans 10"));
      m_FontDialogButton.set_expand(true);
      m_FontDialogButton.set_use_font(true);
      m_FontDialogButton.set_use_size(true);
      m_FontDialogButton.property_font_desc().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_font_button_font_set));

      m_ButtonBox.append(m_Button_Dialog);
      m_Button_Dialog.set_expand(true);
      m_Button_Dialog.signal_clicked().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_dialog_clicked));
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_font_button_font_set()
    {
      auto font_name = m_FontDialogButton.get_font_desc().to_string();
      std::cout << "Font chosen: " << font_name << std::endl;
    }

    void ExampleWindow::on_button_dialog_clicked()
    {
      // Get the previously selected font description from the FontDialogButton.
      m_pDialog->choose_font(*this,
        sigc::mem_fun(*this, &ExampleWindow::on_dialog_finish),
        m_FontDialogButton.get_font_desc());
    }

    void ExampleWindow::on_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result)
    {
      try
      {
        // If this call changes the font, it will trigger a call to
        // on_font_button_font_set().
        m_FontDialogButton.set_font_desc(m_pDialog->choose_font_finish(result));
      }
      catch (const Gtk::DialogError& err)
      {
        // Can be thrown by m_pDialog->choose_font_finish(result).
        std::cout << "No font selected. " << err.what() << std::endl;
      }
      catch (const Glib::Error& err)
      {
        std::cout << "Unexpected exception. " << err.what() << std::endl;
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Non-modal AboutDialog

The AboutDialog offers a simple way to display information about a program, like its logo, name, copyright, website and license.

Most dialogs in this chapter are modal, that is, they freeze the rest of the application while they are shown. It's also possible to create a non-modal dialog, which does not freeze other windows in the application. The following example shows a non-modal AboutDialog. This is perhaps not the kind of dialog you would normally make non-modal, but non-modal dialogs can be useful in other cases. E.g. gedit's search-and-replace dialog is non-modal.

Reference

#### Exemplo

AboutDialog

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_clicked();

      //Child widgets:
      Gtk::Box m_VBox;
      Gtk::Label m_Label;
      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button;
      Gtk::AboutDialog m_Dialog;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Label("The AboutDialog is non-modal. "
        "You can select parts of this text while the AboutDialog is shown."),
      m_ButtonBox(Gtk::Orientation::VERTICAL),
      m_Button("Show AboutDialog")
    {
      set_title("Gtk::AboutDialog example");
      set_default_size(400, 150);

      set_child(m_VBox);

      m_VBox.append(m_Label);
      m_Label.set_expand(true);
      m_Label.set_wrap(true);
      m_Label.set_selectable(true);

      m_VBox.append(m_ButtonBox);
      m_ButtonBox.append(m_Button);
      m_Button.set_expand(true);
      m_Button.set_halign(Gtk::Align::CENTER);
      m_Button.set_valign(Gtk::Align::CENTER);
      m_Button.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_clicked) );

      m_Dialog.set_transient_for(*this);
      m_Dialog.set_hide_on_close();

      m_Dialog.set_logo(Gdk::Texture::create_from_resource("/about/gtkmm_logo.gif"));
      m_Dialog.set_program_name("Example application");
      m_Dialog.set_version("1.0.0");
      m_Dialog.set_copyright("Murray Cumming");
      m_Dialog.set_comments("This is just an example application.");
      m_Dialog.set_license("LGPL");

      m_Dialog.set_website("https://gtkmm.gnome.org");
      m_Dialog.set_website_label("gtkmm website");

      std::vector<Glib::ustring> list_authors;
      list_authors.push_back("Murray Cumming");
      list_authors.push_back("Somebody Else");
      list_authors.push_back("AN Other");
      m_Dialog.set_authors(list_authors);

      m_Button.grab_focus();
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_clicked()
    {
      m_Dialog.set_visible(true);

      //Bring it to the front, in case it was already shown:
      m_Dialog.present();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `aboutdialog.gresource.xml` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <gresources>
      <gresource prefix="/about">
        <file>gtkmm_logo.gif</file>
      </gresource>
    </gresources>

### Custom Dialog

When none of the predefined dialog classes suit your needs, you can make your own dialog by deriving a class from Window and fill it with the widgets you need.

Window Reference

#### Exemplo

Window Dialog

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>
    #include "namedialog.h"

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_button_clicked();
      void on_dialog_response(const Glib::ustring& response);
      void on_dialog_hidden();

      //Child widgets:
      Gtk::Button m_Button;

      NameDialog m_Dialog;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `namedialog.h` (For use with gtkmm 4)

    #ifndef GTKMM_NAME_DIALOG_H_
    #define GTKMM_NAME_DIALOG_H_

    #include <gtkmm.h>

    class NameDialog : public Gtk::Window
    {
    public:
      NameDialog();
      ~NameDialog() override;

      void buttons_clicked_connect(const sigc::slot<void(const Glib::ustring&)>& slot);
      Glib::ustring get_entry1() const;
      Glib::ustring get_entry2() const;

    protected:
      //Member widgets:
      Gtk::Grid m_Grid;
      Gtk::Image m_Image;
      Gtk::Label m_Label1;
      Gtk::Label m_Label2;
      Gtk::Entry m_Entry1;
      Gtk::Entry m_Entry2;
      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_OK;
      Gtk::Button m_Button_Cancel;
    };

    #endif /* GTKMM_NAME_DIALOG_H_ */

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_Button("Show Dialog"),
      m_Dialog()
    {
      set_title("Custom Dialog example");

      set_child(m_Button);
      m_Button.signal_clicked().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_clicked));

      m_Dialog.set_default_size(250, 100);
      m_Dialog.set_transient_for(*this);
      m_Dialog.set_modal();
      m_Dialog.set_hide_on_close();
      m_Dialog.buttons_clicked_connect(
        sigc::mem_fun(*this, &ExampleWindow::on_dialog_response));
      m_Dialog.signal_hide().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_dialog_hidden));
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_clicked()
    {
      m_Dialog.set_visible(true);
    }

    void ExampleWindow::on_dialog_response(const Glib::ustring& response)
    {
      m_Dialog.set_visible(false);

      if (response == "OK")
        std::cout << "Name: " << m_Dialog.get_entry1() << " "
          << m_Dialog.get_entry2() << std::endl;
      else
        std::cout << response << " button clicked" << std::endl;
    }

    void ExampleWindow::on_dialog_hidden()
    {
      std::cout << "Dialog hidden" << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `namedialog.cc` (For use with gtkmm 4)

    NameDialog::NameDialog()
    : m_Label1("_First name", true),
      m_Label2("_Second name", true),
      m_ButtonBox(Gtk::Orientation::HORIZONTAL, 5),
      m_Button_OK("_OK", true),
      m_Button_Cancel("_Cancel", true)
    {
      set_destroy_with_parent(true);

      set_title("Name Dialog");
      set_child(m_Grid);

      m_Grid.set_row_spacing(4);
      m_Grid.set_column_spacing(4);
      m_Grid.set_expand(true);

      m_Image.set_from_icon_name("dialog-question");
      m_Image.set_icon_size(Gtk::IconSize::LARGE);
      m_Grid.attach(m_Image, 0, 0, 1, 2);

      m_Grid.attach(m_Label1, 1, 0);
      m_Grid.attach(m_Entry1, 2, 0);
      m_Label1.set_mnemonic_widget(m_Entry1);

      m_Grid.attach(m_Label2, 1, 1);
      m_Grid.attach(m_Entry2, 2, 1);
      m_Label2.set_mnemonic_widget(m_Entry2);

      m_Grid.attach(m_ButtonBox, 0, 2, 3, 1);
      m_ButtonBox.set_halign(Gtk::Align::END);
      m_ButtonBox.append(m_Button_OK);
      m_ButtonBox.append(m_Button_Cancel);
    }

    void NameDialog::buttons_clicked_connect(
      const sigc::slot<void(const Glib::ustring&)>& slot)
    {
      m_Button_OK.signal_clicked().connect(sigc::bind(slot, "OK"));
      m_Button_Cancel.signal_clicked().connect(sigc::bind(slot, "Cancel"));
    }

    Glib::ustring NameDialog::get_entry1() const
    {
      return m_Entry1.get_text();
    }

    Glib::ustring NameDialog::get_entry2() const
    {
      return m_Entry2.get_text();
    }

    NameDialog::~NameDialog()
    {
    }

## The DrawingArea Widget

The DrawingArea widget is a blank window that gives you the freedom to create any graphic you desire. Along with that freedom comes the responsibility to draw on the widget. When a widget is first shown, or when it is covered and then uncovered again it needs to redraw itself. Most widgets have code to do this, but the DrawingArea does not, allowing you to write your own draw function to determine how the contents of the widget will be drawn. This is done by setting a draw function with a call to the set_draw_func() member function.

GTK uses the Cairo drawing API. With gtkmm, you may use the cairomm C++ API for cairo.

You can draw very sophisticated shapes using Cairo, but the methods to do so are quite basic. Cairo provides methods for drawing straight lines, curved lines, and arcs (including circles). These basic shapes can be combined to create more complex shapes and paths which can be filled with solid colors, gradients, patterns, and other things. In addition, Cairo can perform complex transformations, do compositing of images, and render antialiased text.

Cairo e pango

Although Cairo can render text, it's not meant to be a replacement for Pango. Pango is a better choice if you need to perform more advanced text rendering such as wrapping or ellipsizing text. Drawing text with Cairo should only be done if the text is part of a graphic.

In this section of the tutorial, we'll cover the basic Cairo drawing model, describe each of the basic drawing elements in some detail (with examples), and then present a simple application that uses Cairo to draw a custom clock widget.

### Modelo de desenho com cairo

The basic concept of drawing in Cairo involves defining 'invisible' paths and then stroking or filling them to make them visible.

To do any drawing in gtkmm with Cairo, you must first get a Cairo::Context object. This class holds all of the graphics state parameters that describe how drawing is to be done. This includes information such as line width, color, the surface to draw to, and many other things. This allows the actual drawing functions to take fewer arguments to simplify the interface. Usually, you use the Cairo::Context that you get as input data to the draw function that you set with the call to set_draw_func(). It's also possible to create a Cairo::Context by calling the Gdk::Surface::create_cairo_context() and Gdk::CairoContext::cairo_create() functions. Since Cairo contexts are reference-counted objects, cairo_create() returns a Cairo::RefPtr<Cairo::Context> object. (Note the difference between Gdk::CairoContext and Cairo::Context.)

The following example shows how to set up a Cairo context with a foreground color of red and a width of 2. Any drawing functions that use this context will use these settings.

    Gtk::DrawingArea myArea;
    auto gdkCairoContext = myArea.get_surface()->create_cairo_context();
    auto myContext = gdkCairoContext->cairo_create();
    myContext->set_source_rgb(1.0, 0.0, 0.0);
    myContext->set_line_width(2.0);

Each Cairo::Context is associated with a particular Gdk::Surface, so the first line of the above example creates a Gtk::DrawingArea widget and the next two lines use its associated Gdk::Surface to create a Cairo::Context object. The final two lines change the graphics state of the context.

There are a number of graphics state variables that can be set for a Cairo context. The most common context attributes are color (using set_source_rgb() or set_source_rgba() for translucent colors), line width (using set_line_width()), line dash pattern (using set_dash()), line cap style (using set_line_cap()), and line join style (using set_line_join()), and font styles (using set_font_size(), set_font_face() and others). There are many other settings as well, such as transformation matrices, fill rules, whether to perform antialiasing, and others. For further information, see the cairomm API documentation.

The current state of a Cairo::Context can be saved to an internal stack of saved states and later be restored to the state it was in when you saved it. To do this, use the save() method and the restore() method. This can be useful if you need to temporarily change the line width and color (or any other graphics setting) in order to draw something and then return to the previous settings. In this situation, you could call Cairo::Context::save(), change the graphics settings, draw the lines, and then call Cairo::Context::restore() to restore the original graphics state. Multiple calls to save() and restore() can be nested; each call to restore() restores the state from the matching paired save().

It is good practice to put all modifications to the graphics state between save()/restore() function calls. For example, if you have a function that takes a Cairo::Context reference as an argument, you might implement it as follows:

    void doSomething(const Cairo::RefPtr<Cairo::Context>& context, int x)
    {
        context->save();
        // change graphics state
        // perform drawing operations
        context->restore();
    }

The draw function that you set with a call to set_draw_func() is called with a Cairo context that you shall use for drawing in the Gtk::DrawingArea widget. It is not necessary to save and restore this Cairo context in the draw function.

### Desenho de linhas retas

Now that we understand the basics of the Cairo graphics library, we're almost ready to start drawing. We'll start with the simplest of drawing elements: the straight line. But first you need to know a little bit about Cairo's coordinate system. The origin of the Cairo coordinate system is located in the upper-left corner of the window with positive x values to the right and positive y values going down.

Since the Cairo graphics library was written with support for multiple output targets (the X window system, PNG images, OpenGL, etc), there is a distinction between user-space and device-space coordinates. The mapping between these two coordinate systems defaults to one-to-one so that integer values map roughly to pixels on the screen, but this setting can be adjusted if desired. Sometimes it may be useful to scale the coordinates so that the full width and height of a window both range from 0 to 1 (the 'unit square') or some other mapping that works for your application. This can be done with the Cairo::Context::scale() function.

#### Exemplo

In this example, we'll construct a small but fully functional gtkmm program and draw some lines into the window. The lines are drawn by creating a path and then stroking it. A path is created using the functions Cairo::Context::move_to() and Cairo::Context::line_to(). The function move_to() is similar to the act of lifting your pen off of the paper and placing it somewhere else -- no line is drawn between the point you were at and the point you moved to. To draw a line between two points, use the line_to() function.

After you've finished creating your path, you still haven't drawn anything visible yet. To make the path visible, you must use the function stroke() which will stroke the current path with the line width and style specified in your Cairo::Context object. After stroking, the current path will be cleared so that you can start on your next path.

Many Cairo drawing functions have a _preserve() variant. Normally drawing functions such as clip(), fill(), or stroke() will clear the current path. If you use the _preserve() variant, the current path will be retained so that you can use the same path with the next drawing function.

Área de desenho - Linhas

Source Code

File: `myarea.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_MYAREA_H
    #define GTKMM_EXAMPLE_MYAREA_H

    #include <gtkmm/drawingarea.h>

    class MyArea : public Gtk::DrawingArea
    {
    public:
      MyArea();
      virtual ~MyArea();

    protected:
      void on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);
    };

    #endif // GTKMM_EXAMPLE_MYAREA_H

File: `main.cc` (For use with gtkmm 4)

    #include "myarea.h"
    #include <gtkmm/application.h>
    #include <gtkmm/window.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();

    protected:
      MyArea m_area;
    };

    ExampleWindow::ExampleWindow()
    {
      set_title("DrawingArea");
      set_child(m_area);
    }

    int main(int argc, char** argv)
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `myarea.cc` (For use with gtkmm 4)

    #include "myarea.h"
    #include <cairomm/context.h>

    MyArea::MyArea()
    {
      set_draw_func(sigc::mem_fun(*this, &MyArea::on_draw));
    }

    MyArea::~MyArea()
    {
    }

    void MyArea::on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height)
    {
      // coordinates for the center of the window
      int xc, yc;
      xc = width / 2;
      yc = height / 2;

      cr->set_line_width(10.0);

      // draw red lines out from the center of the window
      cr->set_source_rgb(0.8, 0.0, 0.0);
      cr->move_to(0, 0);
      cr->line_to(xc, yc);
      cr->line_to(0, height);
      cr->move_to(xc, yc);
      cr->line_to(width, yc);
      cr->stroke();
    }

This program contains a single class, MyArea, which is a subclass of Gtk::DrawingArea and contains an on_draw() member function. This function becomes the draw function by a call to set_draw_func() in MyArea's constructor. on_draw() is then called whenever the image in the drawing area needs to be redrawn. It is passed a Cairo::RefPtr pointer to a Cairo::Context that we use for the drawing. The actual drawing code sets the color we want to use for drawing by using set_source_rgb() which takes arguments defining the Red, Green, and Blue components of the desired color (valid values are between 0 and 1). After setting the color, we created a new path using the functions move_to() and line_to(), and then stroked this path with stroke().

Desenho com coordenadas relativas

In the example above we drew everything using absolute coordinates. You can also draw using relative coordinates. For a straight line, this is done with the function Cairo::Context::rel_line_to().

#### Estilos de linha

In addition to drawing basic straight lines, there are a number of things that you can customize about a line. You've already seen examples of setting a line's color and width, but there are others as well.

If you've drawn a series of lines that form a path, you may want them to join together in a certain way. Cairo offers three different ways to join lines together: Miter, Bevel, and Round. These are show below:

Different join types in Cairo

The line join style is set using the function Cairo::Context::set_line_join().

Line ends can have different styles as well. The default style is for the line to start and stop exactly at the destination points of the line. This is called a Butt cap. The other options are Round (uses a round ending, with the center of the circle at the end point) or Square (uses a squared ending, with the center of the square at the end point). This setting is set using the function Cairo::Context::set_line_cap().

There are other things you can customize as well, including creating dashed lines and other things. For more information, see the Cairo API documentation. Dashed lines are shown in the example in the Drawing Curved Lines section.

#### Desenhando linhas finas

If you try to draw one pixel wide lines, you may notice that the line sometimes comes up blurred and wider than it ought to be. This happens because Cairo will try to draw from the selected position, to both sides (half to each), so if you're positioned right on the intersection of the pixels, and want a one pixel wide line, Cairo will try to use half of each adjacent pixel, which isn't possible (a pixel is the smallest unit possible). This happens when the width of the line is an odd number of pixels (not just one pixel).

The trick is to position in the middle of the pixel where you want the line to be drawn, and thus guaranteeing you get the desired results. See Cairo FAQ.

Drawing Area - Thin Lines

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm/window.h>
    #include <gtkmm/box.h>
    #include <gtkmm/checkbutton.h>
    #include "myarea.h"

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_toggled();

    private:
      Gtk::Box m_HBox;
      MyArea m_Area_Lines;
      Gtk::CheckButton m_Button_FixLines;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `myarea.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_MYAREA_H
    #define GTKMM_EXAMPLE_MYAREA_H

    #include <gtkmm/drawingarea.h>

    class MyArea : public Gtk::DrawingArea
    {
    public:
      MyArea();
      virtual ~MyArea();

      void fix_lines(bool fix = true);

    protected:
      void on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);

    private:
      double m_fix;
    };

    #endif // GTKMM_EXAMPLE_MYAREA_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_HBox(Gtk::Orientation::HORIZONTAL),
      m_Button_FixLines("Fix lines")
    {
      set_title("Thin lines example");

      m_HBox.append(m_Area_Lines);
      m_HBox.append(m_Button_FixLines);

      set_child(m_HBox);

      m_Button_FixLines.signal_toggled().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_button_toggled));

      // Synchonize the drawing in m_Area_Lines with the state of the toggle button.
      on_button_toggled();
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_toggled()
    {
      m_Area_Lines.fix_lines(m_Button_FixLines.get_active());
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `myarea.cc` (For use with gtkmm 4)

    #include "myarea.h"

    MyArea::MyArea()
    : m_fix (0)
    {
      set_content_width(200);
      set_content_height(100);
      set_draw_func(sigc::mem_fun(*this, &MyArea::on_draw));
    }

    MyArea::~MyArea()
    {
    }

    void MyArea::on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height)
    {
      cr->set_line_width(1.0);

      // draw one line, every two pixels
      // without the 'fix', you won't notice any space between the lines,
      // since each one will occupy two pixels (width)
      for (int i = 0; i < width; i += 2)
      {
        cr->move_to(i + m_fix, 0);
        cr->line_to(i + m_fix, height);
      }

      cr->stroke();
    }

    // Toogle between both values (0 or 0.5)
    void MyArea::fix_lines(bool fix)
    {
      // to get the width right, we have to draw in the middle of the pixel
      m_fix = fix ? 0.5 : 0.0;

      // force the redraw of the image
      queue_draw();
    }

### Desenhando linhas curvadas

In addition to drawing straight lines Cairo allows you to easily draw curved lines (technically a cubic Bézier spline) using the Cairo::Context::curve_to() and Cairo::Context::rel_curve_to() functions. These functions take coordinates for a destination point as well as coordinates for two 'control' points. This is best explained using an example, so let's dive in.

#### Exemplo

This simple application draws a curve with Cairo and displays the control points for each end of the curve.

Drawing Area - Curve

Source Code

File: `myarea.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_MYAREA_H
    #define GTKMM_EXAMPLE_MYAREA_H

    #include <gtkmm/drawingarea.h>

    class MyArea : public Gtk::DrawingArea
    {
    public:
      MyArea();
      virtual ~MyArea();

    protected:
      void on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);
    };

    #endif // GTKMM_EXAMPLE_MYAREA_H

File: `main.cc` (For use with gtkmm 4)

    #include "myarea.h"
    #include <gtkmm/application.h>
    #include <gtkmm/window.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();

    protected:
      MyArea m_area;
    };

    ExampleWindow::ExampleWindow()
    {
      set_title("DrawingArea");
      set_child(m_area);
    }

    int main(int argc, char** argv)
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `myarea.cc` (For use with gtkmm 4)

    #include "myarea.h"
    #include <cairomm/context.h>
    #include <vector>

    MyArea::MyArea()
    {
      set_draw_func(sigc::mem_fun(*this, &MyArea::on_draw));
    }

    MyArea::~MyArea()
    {
    }

    void MyArea::on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height)
    {
      const double x0=0.1, y0=0.5, // start point
                   x1=0.4, y1=0.9, // control point #1
                   x2=0.6, y2=0.1, // control point #2
                   x3=0.9, y3=0.5; // end point
      const std::vector<double> dashes = {0.08, 0.05};

      // scale to unit square (0 to 1 width and height)
      cr->scale(width, height);

      // draw curve
      cr->set_line_width(0.05);
      cr->move_to(x0, y0);
      cr->curve_to(x1, y1, x2, y2, x3, y3);
      cr->stroke();

      // show first control point (red)
      cr->set_line_width(0.03);
      cr->set_dash(dashes, 0.0);
      cr->set_source_rgba(1.0, 0.2, 0.2, 0.6);
      cr->set_line_cap(Cairo::Context::LineCap::ROUND);
      cr->move_to(x1, y1);
      cr->line_to (x0, y0);
      cr->stroke();

      // show second control point (blue)
      cr->set_source_rgba(0.2, 0.2, 1.0, 0.6);
      cr->set_line_cap(Cairo::Context::LineCap::BUTT);
      cr->move_to(x2, y2);
      cr->line_to (x3, y3);
      cr->stroke();
    }

The only difference between this example and the straight line example is in the on_draw() function, but there are a few new concepts and functions introduced here, so let's examine them briefly.

We make a call to Cairo::Context::scale(), passing in the width and height of the drawing area. This scales the user-space coordinate system such that the width and height of the widget are both equal to 1.0 'units'. There's no particular reason to scale the coordinate system in this case, but sometimes it can make drawing operations easier.

The call to Cairo::Context::curve_to() should be fairly self-explanatory. The first pair of coordinates define the control point for the beginning of the curve. The second set of coordinates define the control point for the end of the curve, and the last set of coordinates define the destination point. To make the concept of control points a bit easier to visualize, a line has been drawn from each control point to the end-point on the curve that it is associated with. Note that these control point lines are both translucent. This is achieved with a variant of set_source_rgb() called set_source_rgba(). This function takes a fourth argument specifying the alpha value of the color (valid values are between 0 and 1).

The control point lines are dashed lines. These are just two possible variations. Dashed lines can be more complicated. For instance the dashes can have different lengths like in dash-dotted lines.

### Drawing Arcs and Circles

With Cairo, the same function is used to draw arcs, circles, or ellipses: Cairo::Context::arc(). This function takes five arguments. The first two are the coordinates of the center point of the arc, the third argument is the radius of the arc, and the final two arguments define the start and end angle of the arc. All angles are defined in radians, so drawing a circle is the same as drawing an arc from 0 to 2 * M_PI radians. An angle of 0 is in the direction of the positive X axis (in user-space). An angle of M_PI/2 radians (90 degrees) is in the direction of the positive Y axis (in user-space). Angles increase in the direction from the positive X axis toward the positive Y axis. So with the default transformation matrix, angles increase in a clockwise direction. (Remember that the positive Y axis points downwards.)

To draw an ellipse, you can scale the current transformation matrix by different amounts in the X and Y directions. For example, to draw an ellipse with center at `x`, `y` and size `width`, `height`:

    context->save();
    context->translate(x, y);
    context->scale(width / 2.0, height / 2.0);
    context->arc(0.0, 0.0, 1.0, 0.0, 2 * M_PI);
    context->restore();

#### Exemplo

Here's an example of a simple program that draws an arc, a circle and an ellipse into a drawing area.

Área de desenho - Arcos

Source Code

File: `myarea.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_MYAREA_H
    #define GTKMM_EXAMPLE_MYAREA_H

    #include <gtkmm/drawingarea.h>

    class MyArea : public Gtk::DrawingArea
    {
    public:
      MyArea();
      virtual ~MyArea();

    protected:
      void on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);
    };

    #endif // GTKMM_EXAMPLE_MYAREA_H

File: `main.cc` (For use with gtkmm 4)

    #include "myarea.h"
    #include <gtkmm/application.h>
    #include <gtkmm/window.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();

    protected:
      MyArea m_area;
    };

    ExampleWindow::ExampleWindow()
    {
      set_title("DrawingArea");
      set_child(m_area);
    }

    int main(int argc, char** argv)
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `myarea.cc` (For use with gtkmm 4)

    #include "myarea.h"
    #include <cairomm/context.h>
    #include <cmath>

    MyArea::MyArea()
    {
      set_draw_func(sigc::mem_fun(*this, &MyArea::on_draw));
    }

    MyArea::~MyArea()
    {
    }

    void MyArea::on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height)
    {
      const int lesser = std::min(width, height);

      // coordinates for the center of the window
      const int xc = width / 2;
      const int yc = height / 2;

      cr->set_line_width(lesser * 0.02);  // outline thickness changes
                                          // with window size

      // first draw a simple unclosed arc
      cr->save();
      cr->arc(width / 3.0, height / 4.0, lesser / 4.0, -(M_PI / 5.0), M_PI);
      cr->close_path();   // line back to start point
      cr->set_source_rgb(0.0, 0.8, 0.0);
      cr->fill_preserve();
      cr->restore();  // back to opaque black
      cr->stroke();   // outline it

      // now draw a circle
      cr->save();
      cr->arc(xc, yc, lesser / 4.0, 0.0, 2.0 * M_PI); // full circle
      cr->set_source_rgba(0.0, 0.0, 0.8, 0.6);    // partially translucent
      cr->fill_preserve();
      cr->restore();  // back to opaque black
      cr->stroke();

      // and finally an ellipse
      double ex, ey, ew, eh;
      // center of ellipse
      ex = xc;
      ey = 3.0 * height / 4.0;
      // ellipse dimensions
      ew = 3.0 * width / 4.0;
      eh = height / 3.0;

      cr->save();

      cr->translate(ex, ey);  // make (ex, ey) == (0, 0)
      cr->scale(ew / 2.0, eh / 2.0);  // for width: ew / 2.0 == 1.0
                                      // for height: eh / 2.0 == 1.0

      cr->arc(0.0, 0.0, 1.0, 0.0, 2 * M_PI);  // 'circle' centered at (0, 0)
                                              // with 'radius' of 1.0

      cr->set_source_rgba(0.8, 0.0, 0.0, 0.7);
      cr->fill_preserve();
      cr->restore();  // back to opaque black
      cr->stroke();
    }

There are a couple of things to note about this example code. Again, the only real difference between this example and the previous ones is the on_draw() function, so we'll limit our focus to that function. In addition, the first part of the function is nearly identical to the previous examples, so we'll skip that portion.

Note that in this case, we've expressed nearly everything in terms of the height and width of the window, including the width of the lines. Because of this, when you resize the window, everything scales with the window. Also note that there are three drawing sections in the function and each is wrapped with a save()/restore() pair so that we're back at a known state after each drawing.

The section for drawing an arc introduces one new function, close_path(). This function will in effect draw a straight line from the current point back to the first point in the path. There is a significant difference between calling close_path() and manually drawing a line back to the starting point, however. If you use close_path(), the lines will be nicely joined together. If you use line_to() instead, the lines will end at the same point, but Cairo won't do any special joining.

Desenhando no sentido anti-horário

The function Cairo::Context::arc_negative() is exactly the same as Cairo::Context::arc() but the angles go the opposite direction.

### Desenhando texto

#### Desenhando texto com pango

Text is drawn via Pango Layouts. The easiest way to create a Pango::Layout is to use Gtk::Widget::create_pango_layout(). Once created, the layout can be manipulated in various ways, including changing the text, font, etc. Finally, the layout can be rendered using the Pango::Layout::show_in_cairo_context() method.

#### Exemplo

Here is an example of a program that draws some text, some of it upside-down. The Printing chapter contains another example of drawing text.

Área de desenho - Texto

Source Code

File: `myarea.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_MYAREA_H
    #define GTKMM_EXAMPLE_MYAREA_H

    #include <gtkmm/drawingarea.h>

    class MyArea : public Gtk::DrawingArea
    {
    public:
      MyArea();
      virtual ~MyArea();

    protected:
      void on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);

    private:
      void draw_rectangle(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);
      void draw_text(const Cairo::RefPtr<Cairo::Context>& cr, int rectangle_width, int rectangle_height);

    };

    #endif // GTKMM_EXAMPLE_MYAREA_H

File: `main.cc` (For use with gtkmm 4)

    #include "myarea.h"
    #include <gtkmm/application.h>
    #include <gtkmm/window.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();

    protected:
      MyArea m_area;
    };

    ExampleWindow::ExampleWindow()
    {
      set_title("Drawing text example");
      set_child(m_area);
    }

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `myarea.cc` (For use with gtkmm 4)

    #include "myarea.h"

    MyArea::MyArea()
    {
      set_draw_func(sigc::mem_fun(*this, &MyArea::on_draw));
    }

    MyArea::~MyArea()
    {
    }

    void MyArea::on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height)
    {
      const int rectangle_width = width;
      const int rectangle_height = height / 2;

      // Draw a black rectangle
      cr->set_source_rgb(0.0, 0.0, 0.0);
      draw_rectangle(cr, rectangle_width, rectangle_height);

      // and some white text
      cr->set_source_rgb(1.0, 1.0, 1.0);
      draw_text(cr, rectangle_width, rectangle_height);

      // flip the image vertically
      // see http://www.cairographics.org/documentation/cairomm/reference/classCairo_1_1Matrix.html
      // the -1 corresponds to the yy part (the flipping part)
      // the height part is a translation (we could have just called cr->translate(0, height) instead)
      // it's height and not height / 2, since we want this to be on the second part of our drawing
      // (otherwise, it would draw over the previous part)
      Cairo::Matrix matrix(1.0, 0.0, 0.0, -1.0, 0.0, height);

      // apply the matrix
      cr->transform(matrix);

      // white rectangle
      cr->set_source_rgb(1.0, 1.0, 1.0);
      draw_rectangle(cr, rectangle_width, rectangle_height);

      // black text
      cr->set_source_rgb(0.0, 0.0, 0.0);
      draw_text(cr, rectangle_width, rectangle_height);
    }

    void MyArea::draw_rectangle(const Cairo::RefPtr<Cairo::Context>& cr,
                                int width, int height)
    {
      cr->rectangle(0, 0, width, height);
      cr->fill();
    }

    void MyArea::draw_text(const Cairo::RefPtr<Cairo::Context>& cr,
                           int rectangle_width, int rectangle_height)
    {
      // https://gnome.pages.gitlab.gnome.org/pangomm/classPango_1_1FontDescription.html
      Pango::FontDescription font;

      font.set_family("Monospace");
      font.set_weight(Pango::Weight::BOLD);

      // https://gnome.pages.gitlab.gnome.org/pangomm/classPango_1_1Layout.html
      auto layout = create_pango_layout("Hi there!");

      layout->set_font_description(font);

      int text_width;
      int text_height;

      //get the text dimensions (it updates the variables -- by reference)
      layout->get_pixel_size(text_width, text_height);

      // Position the text in the middle
      cr->move_to((rectangle_width-text_width)/2, (rectangle_height-text_height)/2);

      layout->show_in_cairo_context(cr);
    }

### Desenhando imagens

There is a method for drawing from a Gdk::Pixbuf to a Cairo::Context. A Gdk::Pixbuf buffer is a useful wrapper around a collection of pixels, which can be read from files, and manipulated in various ways.

Probably the most common way of creating Gdk::Pixbufs is to use Gdk::Pixbuf::create_from_file() or Gdk::Pixbuf::create_from_resource(), which can read an image file, such as a png file into a pixbuf ready for rendering.

The Gdk::Pixbuf can be rendered by setting it as the source pattern of the Cairo context with Gdk::Cairo::set_source_pixbuf(). Then draw the image with either Cairo::Context::paint() (to draw the whole image), or Cairo::Context::rectangle() and Cairo::Context::fill() (to fill the specified rectangle). set_source_pixbuf() is not a member of Cairo::Context. It takes a Cairo::Context as its first parameter.

Here is a small bit of code to tie it all together: (Note that usually you wouldn't load the image every time in the draw signal handler! It's just shown here to keep it all together.)

    void MyArea::on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height)
    {
      auto image = Gdk::Pixbuf::create_from_file("myimage.png");
      // Draw the image at 110, 90, except for the outermost 10 pixels.
      Gdk::Cairo::set_source_pixbuf(cr, image, 100, 80);
      cr->rectangle(110, 90, image->get_width()-20, image->get_height()-20);
      cr->fill();
    }

#### Exemplo

Here is an example of a simple program that draws an image. The program loads the image from a resource file. See the Gio::Resource and glib-compile-resources section. Use glib-compile-resources to compile the resources into a C source file that can be compiled and linked with the C++ code. E.g.

    $ glib-compile-resources --target=resources.c --generate-source image.gresource.xml

Área de desenho - Imagens

Source Code

File: `myarea.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_MYAREA_H
    #define GTKMM_EXAMPLE_MYAREA_H

    #include <gtkmm/drawingarea.h>
    #include <gdkmm/pixbuf.h>

    class MyArea : public Gtk::DrawingArea
    {
    public:
      MyArea();
      virtual ~MyArea();

    protected:
      void on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);

      Glib::RefPtr<Gdk::Pixbuf> m_image;
    };

    #endif // GTKMM_EXAMPLE_MYAREA_H

File: `main.cc` (For use with gtkmm 4)

    #include "myarea.h"
    #include <gtkmm/application.h>
    #include <gtkmm/window.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();

    protected:
      MyArea m_area;
    };

    ExampleWindow::ExampleWindow()
    {
      set_title("DrawingArea");
      set_default_size(300, 200);
      set_child(m_area);
    }

    int main(int argc, char** argv)
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `myarea.cc` (For use with gtkmm 4)

    #include "myarea.h"
    #include <cairomm/context.h>
    #include <giomm/resource.h>
    #include <gdkmm/general.h> // set_source_pixbuf()
    #include <glibmm/fileutils.h>
    #include <iostream>

    MyArea::MyArea()
    {
      try
      {
        // The fractal image has been created by the XaoS program.
        // http://xaos.sourceforge.net
        m_image = Gdk::Pixbuf::create_from_resource("/image/fractal_image.png");
      }
      catch(const Gio::ResourceError& ex)
      {
        std::cerr << "ResourceError: " << ex.what() << std::endl;
      }
      catch(const Gdk::PixbufError& ex)
      {
        std::cerr << "PixbufError: " << ex.what() << std::endl;
      }

      // Show at least a quarter of the image.
      if (m_image)
      {
        set_content_width(m_image->get_width()/2);
        set_content_height(m_image->get_height()/2);
      }

      // Set the draw function.
      set_draw_func(sigc::mem_fun(*this, &MyArea::on_draw));
    }

    MyArea::~MyArea()
    {
    }

    void MyArea::on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height)
    {
      if (!m_image)
        return;

      // Draw the image in the middle of the drawing area, or (if the image is
      // larger than the drawing area) draw the middle part of the image.
      Gdk::Cairo::set_source_pixbuf(cr, m_image,
        (width - m_image->get_width())/2, (height - m_image->get_height())/2);
      cr->paint();
    }

File: `image.gresource.xml` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <gresources>
      <gresource prefix="/image">
        <file>fractal_image.png</file>
      </gresource>
    </gresources>

### Example Application: Creating a Clock with Cairo

Now that we've covered the basics of drawing with Cairo, let's try to put it all together and create a simple application that actually does something. The following example uses Cairo to create a custom Clock widget. The clock has a second hand, a minute hand, and an hour hand, and updates itself every second.

Source Code

File: `clock.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_CLOCK_H
    #define GTKMM_EXAMPLE_CLOCK_H

    #include <gtkmm/drawingarea.h>

    class Clock : public Gtk::DrawingArea
    {
    public:
      Clock();
      virtual ~Clock();

    protected:
      void on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);

      bool on_timeout();

      double m_radius;
      double m_line_width;
    };

    #endif // GTKMM_EXAMPLE_CLOCK_H

File: `clock.cc` (For use with gtkmm 4)

    #include <ctime>
    #include <cmath>
    #include <cairomm/context.h>
    #include <glibmm/main.h>
    #include "clock.h"

    Clock::Clock()
    : m_radius(0.42), m_line_width(0.05)
    {
      Glib::signal_timeout().connect( sigc::mem_fun(*this, &Clock::on_timeout), 1000 );
      set_draw_func(sigc::mem_fun(*this, &Clock::on_draw));
    }

    Clock::~Clock()
    {
    }

    void Clock::on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height)
    {
      // scale to unit square and translate (0, 0) to be (0.5, 0.5), i.e.
      // the center of the window
      cr->scale(width, height);
      cr->translate(0.5, 0.5);
      cr->set_line_width(m_line_width);

      cr->save();
      cr->set_source_rgba(0.337, 0.612, 0.117, 0.9);   // green
      cr->paint();
      cr->restore();
      cr->arc(0, 0, m_radius, 0, 2 * M_PI);
      cr->save();
      cr->set_source_rgba(1.0, 1.0, 1.0, 0.8);
      cr->fill_preserve();
      cr->restore();
      cr->stroke_preserve();
      cr->clip();

      //clock ticks
      for (int i = 0; i < 12; i++)
      {
        double inset = 0.05;

        cr->save();
        cr->set_line_cap(Cairo::Context::LineCap::ROUND);

        if(i % 3 != 0)
        {
          inset *= 0.8;
          cr->set_line_width(0.03);
        }

        cr->move_to(
          (m_radius - inset) * cos (i * M_PI / 6),
          (m_radius - inset) * sin (i * M_PI / 6));
        cr->line_to (
          m_radius * cos (i * M_PI / 6),
          m_radius * sin (i * M_PI / 6));
        cr->stroke();
        cr->restore(); /* stack-pen-size */
      }

      // store the current time
      time_t rawtime;
      time(&rawtime);
      struct tm * timeinfo = localtime (&rawtime);

      // compute the angles of the indicators of our clock
      double minutes = timeinfo->tm_min * M_PI / 30;
      double hours = timeinfo->tm_hour * M_PI / 6;
      double seconds= timeinfo->tm_sec * M_PI / 30;

      cr->save();
      cr->set_line_cap(Cairo::Context::LineCap::ROUND);

      // draw the seconds hand
      cr->save();
      cr->set_line_width(m_line_width / 3);
      cr->set_source_rgba(0.7, 0.7, 0.7, 0.8); // gray
      cr->move_to(0, 0);
      cr->line_to(sin(seconds) * (m_radius * 0.9),
        -cos(seconds) * (m_radius * 0.9));
      cr->stroke();
      cr->restore();

      // draw the minutes hand
      cr->set_source_rgba(0.117, 0.337, 0.612, 0.9);   // blue
      cr->move_to(0, 0);
      cr->line_to(sin(minutes + seconds / 60) * (m_radius * 0.8),
        -cos(minutes + seconds / 60) * (m_radius * 0.8));
      cr->stroke();

      // draw the hours hand
      cr->set_source_rgba(0.337, 0.612, 0.117, 0.9);   // green
      cr->move_to(0, 0);
      cr->line_to(sin(hours + minutes / 12.0) * (m_radius * 0.5),
        -cos(hours + minutes / 12.0) * (m_radius * 0.5));
      cr->stroke();
      cr->restore();

      // draw a little dot in the middle
      cr->arc(0, 0, m_line_width / 3.0, 0, 2 * M_PI);
      cr->fill();
    }

    bool Clock::on_timeout()
    {
      // force our program to redraw the entire clock.
      queue_draw();
      return true;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "clock.h"
    #include <gtkmm/application.h>
    #include <gtkmm/window.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();

    protected:
      Clock m_clock;
    };

    ExampleWindow::ExampleWindow()
    {
      set_title("Cairomm Clock");
      set_child(m_clock);
    }

    int main(int argc, char** argv)
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

As before, almost all of the interesting stuff is done in the draw function on_draw(). Before we dig into the draw function, notice that the constructor for the Clock widget connects a handler function on_timeout() to a timer with a timeout period of 1000 milliseconds (1 second). This means that on_timeout() will get called once per second. The sole responsibility of this function is to invalidate the window so that gtkmm will be forced to redraw it.

Now let's take a look at the code that performs the actual drawing. The first section of on_draw() should be pretty familiar by now. This example again scales the coordinate system to be a unit square so that it's easier to draw the clock as a percentage of window size so that it will automatically scale when the window size is adjusted. Furthermore, the coordinate system is scaled over and down so that the (0, 0) coordinate is in the very center of the window.

The function Cairo::Context::paint() is used here to set the background color of the window. This function takes no arguments and fills the current surface (or the clipped portion of the surface) with the source color currently active. After setting the background color of the window, we draw a circle for the clock outline, fill it with white, and then stroke the outline in black. Notice that both of these actions use the _preserve variant to preserve the current path, and then this same path is clipped to make sure that our next lines don't go outside the outline of the clock.

After drawing the outline, we go around the clock and draw ticks for every hour, with a larger tick at 12, 3, 6, and 9. Now we're finally ready to implement the time-keeping functionality of the clock, which simply involves getting the current values for hours, minutes and seconds, and drawing the hands at the correct angles.

## Arrastar e soltar

The Gtk::DragSource and Gtk::DropTarget event controllers have methods and signals which are used for Drag and Drop.

### Sources and Targets

Things are dragged from `sources` to be dropped on `targets`. Each source and target has information about the data formats that it can send or receive, provided by Gdk::ContentFormats. A drop target will only accept a dragged item if they both share a compatible format. Appropriate signals will then be emitted, telling the signal handlers which format was used.

Gdk::ContentFormats objects contain information about available GTypes and mime types (media types).

### Métodos

Widgets can be identified as sources or targets using Gtk::DragSource and Gtk::DropTarget event controllers.

    auto source = Gtk::DragSource::create();
    m_source_widget.add_controller(source);

Some DragSource methods:

- `void set_content(const Glib::RefPtr<Gdk::ContentProvider>& content)`: Sets a content provider on the drag source.

- `void set_actions(Gdk::DragAction actions)`: Sets the actions on the drag source. For instance `Gdk::DragAction::COPY | Gdk::DragAction::MOVE`.

- `void set_icon(const Glib::RefPtr<const Gdk::Paintable>& paintable, int hot_x, int hot_y)`: Sets a paintable to use as icon during DND operations.

    auto target = Gtk::DropTarget::create(gtype, actions);
    m_target_widget.add_controller(target);

Some DropTarget methods:

- `void set_gtypes(const std::vector<GType>& types)`: Sets the supported types for this drop target.

- `void set_actions(Gdk::DragAction actions)`: Sets the actions that this drop target supports.

- `Glib::ValueBase get_value() const`: Gets the current drop data, as a Glib::Value.

- `void reject()`: Rejects the ongoing drop operation. This function should be used when delaying the decision on whether to accept a drag or not until after reading the data.

### Sinais

When a drop target has accepted a dragged item, certain signals will be emitted, depending on what action has been selected. For instance, the user might have held down the Shift key to specify a `move` rather than a `copy`. Remember that the user can only select the actions which you have specified in your calls to Gtk::DragSource::set_actions() and Gtk::DropTarget::set_actions().

The source widget will emit these DragSource signals:

- `drag_begin`: Provides a Gdk::Drag.

- `prepare`: Shall return a Gdk::ContentProvider, with the data to use for the drag that is about to start.

- `drag_end`: Provides a Gdk::Drag, and a bool that tells if the drag was performing a `move` and the data should be deleted.

- `drag_cancel`: Emitted on the drag source when a drag has failed.

The target widget will emit these DropTarget signals:

- `enter`: Provides coordinates. Shall return the preferred Gdk::DragAction.

- `motion`: Provides coordinates. Shall return the preferred Gdk::DragAction.

- `leave`: Emitted on the drop site when the pointer leaves the widget.

- `accept`: Provides a Gdk::Drop. You can call the status() method of the Gdk::Drop to indicate which actions will be accepted.

- `drop`: Provides the data being dropped and coordinates. Shall return a bool indicating whether the drop was accepted.

The following signals call only one signal handler when emitted. When you connect a handler to such a signal, your signal handler must be called before (instead of) the default handler, otherwise it won't be called. Set the `after` parameter in connect() to `false`.

- Gtk::DragSource::signal_prepare()

- Gtk::DropTarget::signal_enter()

- Gtk::DropTarget::signal_motion()

- Gtk::DropTarget::signal_accept()

- Gtk::DropTarget::signal_drop()

### Exemplo

Here is a very simple example, demonstrating a drag and drop `Copy` operation:

Arrastar e soltar

Source Code

File: `dndwindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_DNDWINDOW_H
    #define GTKMM_EXAMPLE_DNDWINDOW_H

    #include <gdkmm/drop.h>
    #include <gtkmm/box.h>
    #include <gtkmm/label.h>
    #include <gtkmm/window.h>
    #include <gtkmm/button.h>

    class DnDWindow : public Gtk::Window
    {

    public:
      DnDWindow();
      virtual ~DnDWindow();

    protected:
      //Signal handlers:
      Glib::RefPtr<Gdk::ContentProvider> on_label_drag_prepare_data(double x, double y);
      bool on_button_drop_drop_data(const Glib::ValueBase& value, double x, double y);

      //Member widgets:
      Gtk::Box m_HBox;
      Gtk::Label m_Label_Drag;
      Gtk::Button m_Button_Drop;
    };

    #endif // GTKMM_EXAMPLE_DNDWINDOW_H

File: `dndwindow.cc` (For use with gtkmm 4)

    #include "dndwindow.h"
    #include <gdkmm/contentprovider.h>
    #include <gtkmm/dragsource.h>
    #include <gtkmm/droptarget.h>
    #include <iostream>

    DnDWindow::DnDWindow()
    : m_Label_Drag("Drag Here\n"),
      m_Button_Drop("Drop here\n")
    {
      set_title("DnD example");

      set_child(m_HBox);

      //Drag site:

      //Make m_Label_Drag a DnD drag source:
      auto source = Gtk::DragSource::create();
      source->set_actions(Gdk::DragAction::COPY);
      source->signal_prepare().connect(
        sigc::mem_fun(*this, &DnDWindow::on_label_drag_prepare_data), false);
      m_Label_Drag.add_controller(source);

      m_HBox.append(m_Label_Drag);
      m_Label_Drag.set_expand(true);

      //Drop site:

      //Make m_Button_Drop a DnD drop destination:
      const GType ustring_type = Glib::Value<Glib::ustring>::value_type();
      auto target = Gtk::DropTarget::create(ustring_type, Gdk::DragAction::COPY);
      target->signal_drop().connect(
        sigc::mem_fun(*this, &DnDWindow::on_button_drop_drop_data), false);
      m_Button_Drop.add_controller(target);

      m_HBox.append(m_Button_Drop);
      m_Button_Drop.set_expand(true);
    }

    DnDWindow::~DnDWindow()
    {
    }

    // In this simple example where just a small amount of data is copied,
    // it would be reasonable to store the ContentProvider in the DragSource.
    // Then this signal handler would be unnecessary.
    Glib::RefPtr<Gdk::ContentProvider> DnDWindow::on_label_drag_prepare_data(double, double)
    {
      Glib::Value<Glib::ustring> ustring_value;
      ustring_value.init(ustring_value.value_type());
      ustring_value.set("I'm Data!");
      return Gdk::ContentProvider::create(ustring_value);
    }

    bool DnDWindow::on_button_drop_drop_data(const Glib::ValueBase& value, double, double)
    {
      if (G_VALUE_HOLDS(value.gobj(), Glib::Value<Glib::ustring>::value_type()))
      {
        // We got the value type that we expected.
        Glib::Value<Glib::ustring> ustring_value;
        ustring_value.init(value.gobj());
        const Glib::ustring dropped_string = ustring_value.get();

        std::cout << "Received \"" << dropped_string << "\" in button " << std::endl;
        return true;
      }
      else
      {
        std::cout << "Received unexpected data type \""
          << G_VALUE_TYPE_NAME(value.gobj()) << "\" in button " << std::endl;
        return false;
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "dndwindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<DnDWindow>(argc, argv);
    }

There is a more complex example in examples/others/dnd.

## Área de transferência

Simple text copy-paste functionality is provided for free by widgets such as Gtk::Entry and Gtk::TextView, but you might need special code to deal with your own data formats. For instance, a drawing program would need special code to allow copy and paste within a view, or between documents.

You can get a clipboard instance with Gtk::Widget::get_clipboard() or Gdk::Display::get_clipboard().

Your application doesn't need to wait for clipboard operations, particularly between the time when the user chooses Copy and then later chooses Paste. Many Gdk::Clipboard methods take sigc::slots which specify callback methods. When Gdk::Clipboard is ready, it will call these methods, providing the requested data.

Reference

### Formats

Different applications contain different types of data, and they might make that data available in a variety of formats. gtkmm calls these data types `format`s.

For instance, gedit can supply and receive the `text/plain` mime type, so you can paste data into gedit from any application that supplies that format. Or two different image editing applications might supply and receive a variety of image formats. As long as one application can receive one of the formats that the other supplies then you will be able to copy data from one to the other.

Clipboard data can be in a variety of binary formats. This chapter, and the examples, assume that the data is 8-bit text. This would allow us to use an XML format for the clipboard data. However this would probably not be appropriate for binary data such as images.

The Drag and Drop API uses the same mechanism. You should probably use the same data formats for both Clipboard and Drag and Drop operations.

### Copiar

When the user asks to copy some data, you should copy the data to the Clipboard. For instance,

    void ExampleWindow::on_button_copy()
    {
      get_clipboard()->set_text("example_custom_target");
    }

### Colar

When the user asks to paste data from the Clipboard, you should request a specific format and provide a callback method which will be called with the actual data. For instance:

    void ExampleWindow::on_button_paste()
    {
      get_clipboard()->read_text_async(sigc::mem_fun(*this,
                  &ExampleWindow::on_clipboard_received));
    }

Here is an example callback method:

    void ExampleWindow::on_clipboard_received(Glib::RefPtr<Gio::AsyncResult>& result)
    {
      auto text = get_clipboard()->read_text_finish(result);
      //Do something with the pasted data.
    }

#### Discovering the available formats

To find out what formats are currently available on the Clipboard for pasting, call the get_formats() method. Then call a Gdk::ContentFormats method to find out if a format that your application supports is available.

### Examples

#### Simples

This example allows copy and pasting of application-specific data, using the standard text format. Although this is simple, it's not ideal because it does not identify the Clipboard data as being of a particular type.

Área de transferência - Simples

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_copy();
      void on_button_paste();

      void on_clipboard_text_received(Glib::RefPtr<Gio::AsyncResult>& result);

      Glib::ustring m_strData;

      //Child widgets:
      Gtk::Box m_VBox;

      Gtk::Label m_Label;

      Gtk::Grid m_Grid;
      Gtk::ToggleButton m_ButtonA1, m_ButtonA2, m_ButtonB1, m_ButtonB2;

      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Copy, m_Button_Paste;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Label("Select cells in the grid, click Copy, then open a second "
            "instance of this example to try pasting the copied data."),
      m_ButtonA1("A1"), m_ButtonA2("A2"), m_ButtonB1("B1"), m_ButtonB2("B2"),
      m_Button_Copy("_Copy", /* mnemonic= */ true), m_Button_Paste("_Paste", true)
    {
      set_title("Gtk::Clipboard example");

      m_VBox.set_margin(12);
      set_child(m_VBox);

      m_VBox.append(m_Label);

      //Fill Grid:
      m_VBox.append(m_Grid);
      m_Grid.set_expand(true);
      m_Grid.set_row_homogeneous(true);
      m_Grid.set_column_homogeneous(true);
      m_Grid.attach(m_ButtonA1, 0, 0);
      m_Grid.attach(m_ButtonA2, 1, 0);
      m_Grid.attach(m_ButtonB1, 0, 1);
      m_Grid.attach(m_ButtonB2, 1, 1);

      //Add ButtonBox to bottom:
      m_VBox.append(m_ButtonBox);
      m_VBox.set_spacing(6);

      //Fill ButtonBox:
      m_ButtonBox.append(m_Button_Copy);
      m_Button_Copy.set_hexpand(true);
      m_Button_Copy.set_halign(Gtk::Align::END);
      m_Button_Copy.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_copy) );
      m_ButtonBox.append(m_Button_Paste);
      m_Button_Paste.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_paste) );
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_copy()
    {
      //Build a string representation of the stuff to be copied:
      //Ideally you would use XML, with an XML parser here:
      m_strData = m_ButtonA1.get_active() ? "1" : "0";
      m_strData += m_ButtonA2.get_active() ? "1" : "0";
      m_strData += m_ButtonB1.get_active() ? "1" : "0";
      m_strData += m_ButtonB2.get_active() ? "1" : "0";

      // Gdk::Clipboard::set_text() does not take a copy of the text.
      // The text can only be pasted (in this program or in some other program)
      // for as long as it exists.
      get_clipboard()->set_text(m_strData);
    }

    void ExampleWindow::on_button_paste()
    {
      //Tell the clipboard to call our method when it is ready:
      get_clipboard()->read_text_async(sigc::mem_fun(*this,
                  &ExampleWindow::on_clipboard_text_received));
    }

    void ExampleWindow::on_clipboard_text_received(Glib::RefPtr<Gio::AsyncResult>& result)
    {
      Glib::ustring text;
      try
      {
        text = get_clipboard()->read_text_finish(result);
      }
      catch (const Glib::Error& err)
      {
        // Print an error about why pasting failed.
        // Usually you probably want to ignore such failures,
        // but for demonstration purposes, we show the error.
        std::cout << "Pasting failed: " << err.what() << std::endl;
      }

      //See comment in on_button_copy() about this silly clipboard format.
      if(text.size() >= 4)
      {
        m_ButtonA1.set_active( text[0] == '1' );
        m_ButtonA2.set_active( text[1] == '1' );
        m_ButtonB1.set_active( text[2] == '1' );
        m_ButtonB2.set_active( text[3] == '1' );
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      // Gio::Application::Flags::NON_UNIQUE because it shall be possible to run
      // several instances of this application simultaneously.
      auto app = Gtk::Application::create(
        "org.gtkmm.example", Gio::Application::Flags::NON_UNIQUE);

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

#### Ideal

This is like the simple example, but it

1. Defines a custom clipboard target, though the format is still text.

2. It uses the Gdk::ContentFormats::signal_changed() signal and disables the Paste button if it can't use anything on the clipboard.

Área de transferência - Ideal

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_copy();
      void on_button_paste();

      void on_clipboard_content_changed();

      void on_clipboard_received(Glib::RefPtr<Gio::AsyncResult>& result);
      void on_clipboard_received_status(Glib::RefPtr<Gio::AsyncResult>& result);

      void update_paste_status(); //Disable the paste button if there is nothing to paste.

      Glib::ustring m_strData;

      //Child widgets:
      Gtk::Box m_VBox;

      Gtk::Label m_Label;

      Gtk::Grid m_Grid;
      Gtk::ToggleButton m_ButtonA1, m_ButtonA2, m_ButtonB1, m_ButtonB2;

      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Copy, m_Button_Paste;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>
    #include <string>

    namespace
    {

    const char example_format_custom[] = "gtkmmclipboardexample";

    } // anonymous namespace

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Label("Select cells in the grid, click Copy, then open a second instance "
              "of this example to try pasting the copied data.\nOr try pasting the "
              "text representation into gedit."),
      m_ButtonA1("A1"), m_ButtonA2("A2"), m_ButtonB1("B1"), m_ButtonB2("B2"),
      m_Button_Copy("_Copy", /* mnemonic= */ true), m_Button_Paste("_Paste", true)
    {
      set_title("Gtk::Clipboard example");

      m_VBox.set_margin(12);
      set_child(m_VBox);

      m_VBox.append(m_Label);

      //Fill Grid:
      m_VBox.append(m_Grid);
      m_Grid.set_expand(true);
      m_Grid.set_row_homogeneous(true);
      m_Grid.set_column_homogeneous(true);
      m_Grid.attach(m_ButtonA1, 0, 0);
      m_Grid.attach(m_ButtonA2, 1, 0);
      m_Grid.attach(m_ButtonB1, 0, 1);
      m_Grid.attach(m_ButtonB2, 1, 1);

      //Add ButtonBox to bottom:
      m_VBox.append(m_ButtonBox);
      m_VBox.set_spacing(6);

      //Fill ButtonBox:
      m_ButtonBox.append(m_Button_Copy);
      m_Button_Copy.set_hexpand(true);
      m_Button_Copy.set_halign(Gtk::Align::END);
      m_Button_Copy.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_copy) );
      m_ButtonBox.append(m_Button_Paste);
      m_Button_Paste.signal_clicked().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_button_paste) );

      //Connect a signal handler that will be called when the contents of
      //the clipboard change.
      get_clipboard()->signal_changed().connect(sigc::mem_fun(*this,
                  &ExampleWindow::on_clipboard_content_changed));

      update_paste_status();
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_copy()
    {
      //Build a string representation of the stuff to be copied:
      //Ideally you would use XML, with an XML parser here:
      m_strData = example_format_custom;
      m_strData += m_ButtonA1.get_active() ? " A1" : "";
      m_strData += m_ButtonA2.get_active() ? " A2" : "";
      m_strData += m_ButtonB1.get_active() ? " B1" : "";
      m_strData += m_ButtonB2.get_active() ? " B2" : "";

      // Gdk::Clipboard::set_text() does not take a copy of the text.
      // The text can only be pasted (in this program or in some other program)
      // for as long as it exists.
      get_clipboard()->set_text(m_strData);
    }

    void ExampleWindow::on_button_paste()
    {
      //Tell the clipboard to call our method when it is ready:
      get_clipboard()->read_text_async(sigc::mem_fun(*this,
                  &ExampleWindow::on_clipboard_received));
    }

    void ExampleWindow::on_clipboard_content_changed()
    {
      update_paste_status();
    }

    void ExampleWindow::on_clipboard_received(Glib::RefPtr<Gio::AsyncResult>& result)
    {
      Glib::ustring text;
      try
      {
        text = get_clipboard()->read_text_finish(result);
      }
      catch (const Glib::Error& err)
      {
        // Print an error about why pasting failed.
        // Usually you probably want to ignore such failures,
        // but for demonstration purposes, we show the error.
        std::cout << "Pasting failed: " << err.what() << std::endl;
      }

      if (text.find(example_format_custom) == 0)
      {
        // It's the expected format.
        m_ButtonA1.set_active(text.find("A1") != std::string::npos);
        m_ButtonA2.set_active(text.find("A2") != std::string::npos);
        m_ButtonB1.set_active(text.find("B1") != std::string::npos);
        m_ButtonB2.set_active(text.find("B2") != std::string::npos);
      }
      else
      {
        // Unexpected format. Disable the Paste button.
        std::cout << "Unexpected pasted text: \"" << text << "\"" << std::endl;
        m_Button_Paste.set_sensitive(false);
      }
    }

    void ExampleWindow::update_paste_status()
    {
      // Disable the paste button if there is nothing to paste.
      get_clipboard()->read_text_async(sigc::mem_fun(*this,
                  &ExampleWindow::on_clipboard_received_status));
    }

    void ExampleWindow::on_clipboard_received_status(Glib::RefPtr<Gio::AsyncResult>& result)
    {
      Glib::ustring text;
      try
      {
        text = get_clipboard()->read_text_finish(result);
      }
      catch (const Glib::Error&)
      {
      }

      const bool bPasteIsPossible = text.find(example_format_custom) == 0;

      // Enable/Disable the Paste button appropriately:
      m_Button_Paste.set_sensitive(bPasteIsPossible);
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      // Gio::Application::Flags::NON_UNIQUE because it shall be possible to run
      // several instances of this application simultaneously.
      auto app = Gtk::Application::create(
        "org.gtkmm.example", Gio::Application::Flags::NON_UNIQUE);

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

## Imprimindo

At the application development level, gtkmm's printing API provides dialogs that are consistent across applications and allows use of Cairo's common drawing API, with Pango-driven text rendering. In the implementation of this common API, platform-specific backends and printer-specific drivers are used.

### PrintOperation

The primary object is Gtk::PrintOperation, allocated for each print operation. To handle page drawing connect to its signals, or inherit from it and override the default virtual signal handlers. PrintOperation automatically handles all the settings affecting the print loop.

#### Sinais

The PrintOperation::run() method starts the print loop, during which various signals are emitted:

- `begin_print`: You must handle this signal, because this is where you create and set up a Pango::Layout using the provided Gtk::PrintContext, and break up your printing output into pages.

- `paginate`: Pagination is potentially slow so if you need to monitor it you can call the PrintOperation::set_show_progress() method and handle this signal.

- For each page that needs to be rendered, the following signals are emitted:

  - `request_page_setup`: Provides a PrintContext, page number and Gtk::PageSetup. Handle this signal if you need to modify page setup on a per-page basis.

  - `draw_page`: You must handle this signal, which provides a PrintContext and a page number. The PrintContext should be used to create a Cairo::Context into which the provided page should be drawn. To render text, iterate over the Pango::Layout you created in the `begin_print` handler.

- `end_print`: A handler for it is a safe place to free any resources related to a PrintOperation. If you have your custom class that inherits from PrintOperation, it is naturally simpler to do it in the destructor.

- `done`: This signal is emitted when printing is finished, meaning when the print data is spooled. Note that the provided `Gtk::PrintOperation::Result` may indicate that an error occurred. In any case you probably want to notify the user about the final status.

- `status_changed`: Emitted whenever a print job's status changes, until it is finished. Call the PrintOperation::set_track_print_status() method to monitor the job status after spooling. To see the status, use get_status() or get_status_string().

Reference

### Configurar página

The PrintOperation class has a method called set_default_page_setup() which selects the default paper size, orientation and margins. To show a page setup dialog from your application, use the Gtk::run_page_setup_dialog() method, which returns a Gtk::PageSetup object with the chosen settings. Use this object to update a PrintOperation and to access the selected Gtk::PaperSize, `Gtk::PageOrientation` and printer-specific margins.

You should save the chosen Gtk::PageSetup so you can use it again if the page setup dialog is shown again.

Por exemplo,

    // Within a class that inherits from Gtk::Window and keeps m_refPageSetup
    // and m_refSettings as members...
    auto new_page_setup = Gtk::run_page_setup_dialog(*this, m_refPageSetup, m_refSettings);
    m_refPageSetup = new_page_setup;

Reference

The Cairo coordinate system, in the `draw_page` handler, is automatically rotated to the current page orientation. It is normally within the printer margins, but you can change that via the PrintOperation::set_use_full_page() method. The default measurement unit is device pixels. To select other units, use the PrintOperation::set_unit() method.

### Processamento de texto

Text rendering is done using Pango. The Pango::Layout object for printing should be created by calling the PrintContext::create_pango_layout() method. The PrintContext object also provides the page metrics, via get_width() and get_height(). The number of pages can be set with PrintOperation::set_n_pages(). To actually render the Pango text in `on_draw_page`, get a Cairo::Context with PrintContext::get_cairo_context() and show the Pango::LayoutLines that appear within the requested page number.

See an example of exactly how this can be done.

### Operações assíncronas

By default, PrintOperation::run() returns when a print operation is completed. If you need to run a non-blocking print operation, call PrintOperation::set_allow_async(). Note that set_allow_async() is not supported on all platforms, however the `done` signal will still be emitted.

run() may return `PrintOperation::Result::IN_PROGRESS`. To track status and handle the result or error you need to implement signal handlers for the `done` and `status_changed` signals:

Por exemplo,

    // in class ExampleWindow's method...
    auto op = PrintOperation::create();
    // ...set up op...
    op->signal_done().connect(sigc::bind(sigc::mem_fun(
      *this, &ExampleWindow::on_printoperation_done), op));
    // run the op

Second, check for an error and connect to the `status_changed` signal. For instance:

    void ExampleWindow::on_printoperation_done(Gtk::PrintOperation::Result result,
      const Glib::RefPtr<PrintOperation>& op)
    {
      if (result == Gtk::PrintOperation::Result::ERROR)
        //notify user
      else if (result == Gtk::PrintOperation::Result::APPLY)
        //Update PrintSettings with the ones used in this PrintOperation

      if (! op->is_finished())
        op->signal_status_changed().connect(sigc::bind(sigc::mem_fun(
          *this, &ExampleWindow::on_printoperation_status_changed), op));
    }

Finally, check the status. For instance,

    void ExampleWindow::on_printoperation_status_changed(const Glib::RefPtr<PrintOperation>& op)
    {
      if (op->is_finished())
        //the print job is finished
      else
        //get the status with get_status() or get_status_string()

      //update UI
    }

### Exportar para PDF

The 'Print to file' option is available in the print dialog, without the need for extra implementation. However, it is sometimes useful to generate a pdf file directly from code. For instance,

    auto op = Gtk::PrintOperation::create();
    // ...set up op...
    op->set_export_filename("test.pdf");
    auto res = op->run(Gtk::PrintOperation::Action::EXPORT);

### Estendendo o diálogo de impressão

You may add a custom tab to the print dialog:

- Set the title of the tab via PrintOperation::set_custom_tab_label(), create a new widget and return it from the `create_custom_widget` signal handler. You'll probably want this to be a container widget, packed with some others.

- Get the data from the widgets in the `custom_widget_apply` signal handler.

Although the `custom_widget_apply` signal provides the widget you previously created, to simplify things you can keep the widgets you expect to contain some user input as class members. For example, let's say you have a Gtk::Entry called `m_Entry` as a member of your CustomPrintOperation class:

    Gtk::Widget* CustomPrintOperation::on_create_custom_widget()
    {
      set_custom_tab_label("My custom tab");

      auto hbox = new Gtk::Box(Gtk::Orientation::HORIZONTAL, 8);
      hbox->set_margin(6);

      auto label = Gtk::make_managed<Gtk::Label>("Enter some text: ");
      hbox->append(*label);

      hbox->append(m_Entry);

      return hbox;
    }

    void CustomPrintOperation::on_custom_widget_apply(Gtk::Widget* /* widget */)
    {
      auto user_input = m_Entry.get_text();
      //...
    }

The example in examples/book/printing/advanced demonstrates this.

### Visualização

The native GTK print dialog has a preview button, but you may also start a preview directly from an application:

    // in a class that inherits from Gtk::Window...
    auto op = PrintOperation::create();
    // ...set up op...
    op->run(Gtk::PrintOperation::Action::PREVIEW, *this);

On Unix, the default preview handler uses an external viewer program. On Windows, the native preview dialog will be shown. If necessary you may override this behavior and provide a custom preview dialog. See the example located in /examples/book/printing/advanced.

### PrintDialog

Since gtkmm 4.14 Gtk::PrintDialog is an alternative to Gtk::PrintOperation. PrintDialog uses the same PageSetup and PrintSettings classes as PrintOperation. The rendering with Cairo and Pango is also similar.

### Examples

#### Simples

The following example demonstrates how to print some input from a user interface using PrintOperation. It shows how to implement `on_begin_print` and `on_draw_page`, as well as how to track print status and update the print settings.

Impressão - Simples

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    // This file is part of the printing/simple and printing/advanced examples

    #include <gtkmm.h>

    class PrintFormOperation;

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow(const Glib::RefPtr<Gtk::Application>& app);
      virtual ~ExampleWindow();

    protected:

      void build_main_menu(const Glib::RefPtr<Gtk::Application>& app);

      void print_or_preview(Gtk::PrintOperation::Action print_action);

      //PrintOperation signal handlers.
      //We handle these so can get necessary information to update the UI or print settings.
      //Our derived PrintOperation class also overrides some default signal handlers.
      void on_printoperation_status_changed();
      void on_printoperation_done(Gtk::PrintOperation::Result result);

      //Action signal handlers:
      void on_menu_file_new();
      void on_menu_file_page_setup();
      void on_menu_file_print_preview();
      void on_menu_file_print();
      void on_menu_file_quit();

      //Printing-related objects:
      Glib::RefPtr<Gtk::PageSetup> m_refPageSetup;
      Glib::RefPtr<Gtk::PrintSettings> m_refSettings;
      Glib::RefPtr<PrintFormOperation> m_refPrintFormOperation;

      //Child widgets:
      Gtk::Box m_VBox;
      Gtk::Grid m_Grid;

      Gtk::Label m_NameLabel;
      Gtk::Entry m_NameEntry;

      Gtk::Label m_SurnameLabel;
      Gtk::Entry m_SurnameEntry;

      Gtk::Label m_CommentsLabel;
      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::TextView m_TextView;

      Glib::RefPtr<Gtk::TextBuffer> m_refTextBuffer;

      Gtk::Label m_Statusbar;

      Glib::RefPtr<Gtk::Builder> m_refBuilder;

      Glib::RefPtr<Gtk::AlertDialog> m_refDialog;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `printformoperation.h` (For use with gtkmm 4)

    #ifndef GTKMM_PRINT_FORM_OPERATION_H
    #define GTKMM_PRINT_FORM_OPERATION_H

    #include <gtkmm.h>
    #include <pangomm.h>
    #include <vector>

    //We derive our own class from PrintOperation,
    //so we can put the actual print implementation here.
    class PrintFormOperation : public Gtk::PrintOperation
    {
     public:
      static Glib::RefPtr<PrintFormOperation> create();
      virtual ~PrintFormOperation();

      void set_name(const Glib::ustring& name) { m_Name = name; }
      void set_comments(const Glib::ustring& comments) { m_Comments = comments; }

     protected:
      PrintFormOperation();

      //PrintOperation default signal handler overrides:
      void on_begin_print(const Glib::RefPtr<Gtk::PrintContext>& context) override;
      void on_draw_page(const Glib::RefPtr<Gtk::PrintContext>& context, int page_nr) override;

      Glib::ustring m_Name;
      Glib::ustring m_Comments;
      Glib::RefPtr<Pango::Layout> m_refLayout;
      std::vector<int> m_PageBreaks; // line numbers where a page break occurs
    };

    #endif // GTKMM_PRINT_FORM_OPERATION_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include "printformoperation.h"
    #include <iostream>

    ExampleWindow::ExampleWindow(const Glib::RefPtr<Gtk::Application>& app)
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_NameLabel("Name"),
      m_SurnameLabel("Surname"),
      m_CommentsLabel("Comments")
    {
      m_refPageSetup = Gtk::PageSetup::create();
      m_refSettings = Gtk::PrintSettings::create();

      set_title("gtkmm Printing Example");
      set_default_size(400, 300);

      set_child(m_VBox);

      build_main_menu(app);

      m_VBox.append(m_Grid);

      //Arrange the widgets inside the grid:
      m_Grid.set_expand(true);
      m_Grid.set_row_spacing(5);
      m_Grid.set_column_spacing(5);
      m_Grid.attach(m_NameLabel, 0, 0);
      m_Grid.attach(m_NameEntry, 1, 0);

      m_Grid.attach(m_SurnameLabel, 0, 1);
      m_Grid.attach(m_SurnameEntry, 1, 1);

      //Add the TextView, inside a ScrolledWindow:
      m_ScrolledWindow.set_child(m_TextView);

      //Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);

      m_Grid.attach(m_CommentsLabel, 0, 2);
      m_Grid.attach(m_ScrolledWindow, 1, 2);
      m_ScrolledWindow.set_expand(true);

      m_refTextBuffer = Gtk::TextBuffer::create();
      m_TextView.set_buffer(m_refTextBuffer);

      m_Statusbar.set_hexpand(true);
      m_VBox.append(m_Statusbar);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::build_main_menu(const Glib::RefPtr<Gtk::Application>& app)
    {
      //Create actions for menus and toolbars:
      auto refActionGroup = Gio::SimpleActionGroup::create();

      //File menu:
      refActionGroup->add_action("new",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_new));

      refActionGroup->add_action("pagesetup",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_page_setup));

      refActionGroup->add_action("printpreview",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_print_preview));

      refActionGroup->add_action("print",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_print));

      refActionGroup->add_action("quit",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_quit));

      insert_action_group("example", refActionGroup);

      // When the menubar is a child of a Gtk::Window, keyboard accelerators are not
      // automatically fetched from the Gio::Menu.
      // See the examples/book/menus/main_menu example for an alternative way of
      // adding the menubar when using Gtk::ApplicationWindow.
      app->set_accel_for_action("example.new", "<Primary>n");
      app->set_accel_for_action("example.print", "<Primary>p");
      app->set_accel_for_action("example.quit", "<Primary>q");

      m_refBuilder = Gtk::Builder::create();

      // Layout the actions in a menubar:
      Glib::ustring ui_menu_info =
        "<interface>"
        "  <menu id='menu-example'>"
        "    <submenu>"
        "      <attribute name='label' translatable='yes'>_File</attribute>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_New</attribute>"
        "          <attribute name='action'>example.new</attribute>"
        "        </item>"
        "      </section>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>Page _Setup...</attribute>"
        "          <attribute name='action'>example.pagesetup</attribute>"
        "        </item>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>Print Preview</attribute>"
        "          <attribute name='action'>example.printpreview</attribute>"
        "        </item>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_Print...</attribute>"
        "          <attribute name='action'>example.print</attribute>"
        "        </item>"
        "      </section>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_Quit</attribute>"
        "          <attribute name='action'>example.quit</attribute>"
        "        </item>"
        "      </section>"
        "    </submenu>"
        "  </menu>"
        "</interface>";

      try
      {
        m_refBuilder->add_from_string(ui_menu_info);
      }
      catch(const Glib::Error& ex)
      {
        std::cerr << "building menus failed: " << ex.what();
      }

      // Layout the actions in a toolbar:
      Glib::ustring ui_toolbar_info =
        "<!-- Generated with glade 3.18.3 and then changed manually -->"
        "<interface>"
          "<object class='GtkBox' id='toolbar'>"
            "<property name='can_focus'>False</property>"
            "<property name='spacing'>3</property>"
            "<child>"
              "<object class='GtkButton' id='toolbutton_new'>"
                "<property name='can_focus'>False</property>"
                "<property name='tooltip_text' translatable='yes'>New</property>"
                "<property name='action_name'>example.new</property>"
                "<property name='icon_name'>document-new</property>"
                "<property name='hexpand'>False</property>"
                "<property name='vexpand'>False</property>"
              "</object>"
            "</child>"
            "<child>"
              "<object class='GtkButton' id='toolbutton_print'>"
                "<property name='can_focus'>False</property>"
                "<property name='tooltip_text' translatable='yes'>Print</property>"
                "<property name='action_name'>example.print</property>"
                "<property name='icon_name'>document-print</property>"
                "<property name='hexpand'>False</property>"
                "<property name='vexpand'>False</property>"
              "</object>"
            "</child>"
            "<child>"
              "<object class='GtkSeparator' id='separator1'>"
                "<property name='can_focus'>False</property>"
                "<property name='hexpand'>False</property>"
                "<property name='vexpand'>False</property>"
              "</object>"
            "</child>"
            "<child>"
              "<object class='GtkButton' id='toolbutton_quit'>"
                "<property name='can_focus'>False</property>"
                "<property name='tooltip_text' translatable='yes'>Quit</property>"
                "<property name='action_name'>example.quit</property>"
                "<property name='icon_name'>application-exit</property>"
                "<property name='hexpand'>False</property>"
                "<property name='vexpand'>False</property>"
              "</object>"
            "</child>"
          "</object>"
        "</interface>";

      try
      {
        m_refBuilder->add_from_string(ui_toolbar_info);
      }
      catch(const Glib::Error& ex)
      {
        std::cerr << "building toolbar failed: " << ex.what();
      }

      // Get the menubar and add it to a container widget:
      auto object = m_refBuilder->get_object("menu-example");
      auto gmenu = std::dynamic_pointer_cast<Gio::Menu>(object);
      if (!gmenu)
        g_warning("GMenu not found");
      else
      {
        auto pMenuBar = Gtk::make_managed<Gtk::PopoverMenuBar>(gmenu);

        // Add the PopoverMenuBar to the window:
        m_VBox.append(*pMenuBar);
      }

      // Get the toolbar and add it to a container widget:
      auto toolbar = m_refBuilder->get_widget<Gtk::Box>("toolbar");
      if (!toolbar)
        g_warning("toolbar not found");
      else
        m_VBox.append(*toolbar);
    }

    void ExampleWindow::on_printoperation_status_changed()
    {
      Glib::ustring status_msg;

      if (m_refPrintFormOperation->is_finished())
      {
        status_msg = "Print job completed.";
      }
      else
      {
        //You could also use get_status().
        status_msg = m_refPrintFormOperation->get_status_string();
      }

      m_Statusbar.set_text(status_msg);
    }

    void ExampleWindow::on_printoperation_done(Gtk::PrintOperation::Result result)
    {
      //Printing is "done" when the print data is spooled.

      if (result == Gtk::PrintOperation::Result::ERROR)
      {
        if (!m_refDialog)
          m_refDialog = Gtk::AlertDialog::create("Error printing form");
        m_refDialog->show(*this);
      }
      else if (result == Gtk::PrintOperation::Result::APPLY)
      {
        //Update PrintSettings with the ones used in this PrintOperation:
        m_refSettings = m_refPrintFormOperation->get_print_settings();
      }

      if (!m_refPrintFormOperation->is_finished())
      {
        //We will connect to the status-changed signal to track status
        //and update a status bar. In addition, you can, for example,
        //keep a list of active print operations, or provide a progress dialog.
        m_refPrintFormOperation->signal_status_changed().connect(sigc::mem_fun(*this,
                        &ExampleWindow::on_printoperation_status_changed));
      }
    }

    void ExampleWindow::print_or_preview(Gtk::PrintOperation::Action print_action)
    {
      //Create a new PrintOperation with our PageSetup and PrintSettings:
      //(We use our derived PrintOperation class)
      m_refPrintFormOperation = PrintFormOperation::create();

      m_refPrintFormOperation->set_name(m_NameEntry.get_text() + " " + m_SurnameEntry.get_text());
      m_refPrintFormOperation->set_comments(m_refTextBuffer->get_text(false /*Don't include hidden*/));
      // In the printing/advanced example, the font will be set through a custom tab
      // in the print dialog.

      m_refPrintFormOperation->set_track_print_status();
      m_refPrintFormOperation->set_default_page_setup(m_refPageSetup);
      m_refPrintFormOperation->set_print_settings(m_refSettings);

      m_refPrintFormOperation->signal_done().connect(sigc::mem_fun(*this,
                      &ExampleWindow::on_printoperation_done));
      try
      {
        m_refPrintFormOperation->run(print_action /* print or preview */, *this);
      }
      catch (const Gtk::PrintError& ex)
      {
        //See documentation for exact Gtk::PrintError error codes.
        std::cerr << "An error occurred while trying to run a print operation:"
            << ex.what() << std::endl;
      }
    }

    void ExampleWindow::on_menu_file_new()
    {
      //Clear entries and textview:
      m_NameEntry.set_text("");
      m_SurnameEntry.set_text("");
      m_refTextBuffer->set_text("");
      m_TextView.set_buffer(m_refTextBuffer);
    }

    void ExampleWindow::on_menu_file_page_setup()
    {
      //Show the page setup dialog, asking it to start with the existing settings:
      auto new_page_setup =
          Gtk::run_page_setup_dialog(*this, m_refPageSetup, m_refSettings);

      //Save the chosen page setup dialog for use when printing, previewing, or
      //showing the page setup dialog again:
      m_refPageSetup = new_page_setup;
    }

    void ExampleWindow::on_menu_file_print_preview()
    {
      print_or_preview(Gtk::PrintOperation::Action::PREVIEW);
    }

    void ExampleWindow::on_menu_file_print()
    {
      print_or_preview(Gtk::PrintOperation::Action::PRINT_DIALOG);
    }

    void ExampleWindow::on_menu_file_quit()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv, app);
    }

File: `printformoperation.cc` (For use with gtkmm 4)

    #include "printformoperation.h"

    PrintFormOperation::PrintFormOperation()
    {
    }

    PrintFormOperation::~PrintFormOperation()
    {
    }

    Glib::RefPtr<PrintFormOperation> PrintFormOperation::create()
    {
      return Glib::make_refptr_for_instance<PrintFormOperation>(new PrintFormOperation());
    }

    void PrintFormOperation::on_begin_print(
            const Glib::RefPtr<Gtk::PrintContext>& print_context)
    {
      //Create and set up a Pango layout for PrintData based on the passed
      //PrintContext: We then use this to calculate the number of pages needed, and
      //the lines that are on each page.
      m_refLayout = print_context->create_pango_layout();

      Pango::FontDescription font_desc("sans 12");
      m_refLayout->set_font_description(font_desc);

      const double width = print_context->get_width();
      const double height = print_context->get_height();

      m_refLayout->set_width(static_cast<int>(width * Pango::SCALE));

      //Set and mark up the text to print:
      Glib::ustring marked_up_form_text;
      marked_up_form_text += "<b>Name</b>: " + m_Name + "\n\n";
      marked_up_form_text += "<b>Comments</b>: " + m_Comments;

      m_refLayout->set_markup(marked_up_form_text);

      //Set the number of pages to print by determining the line numbers
      //where page breaks occur:
      const int line_count = m_refLayout->get_line_count();

      Glib::RefPtr<Pango::LayoutLine> layout_line;
      double page_height = 0;

      for (int line = 0; line < line_count; ++line)
      {
        Pango::Rectangle ink_rect, logical_rect;

        layout_line = m_refLayout->get_line(line);
        layout_line->get_extents(ink_rect, logical_rect);

        const double line_height = logical_rect.get_height() / 1024.0;

        if (page_height + line_height > height)
        {
          m_PageBreaks.push_back(line);
          page_height = 0;
        }

        page_height += line_height;
      }

      set_n_pages(m_PageBreaks.size() + 1);
    }

    void PrintFormOperation::on_draw_page(
            const Glib::RefPtr<Gtk::PrintContext>& print_context, int page_nr)
    {
      //Decide which lines we need to print in order to print the specified page:
      int start_page_line = 0;
      int end_page_line = 0;

      if(page_nr == 0)
      {
        start_page_line = 0;
      }
      else
      {
        start_page_line = m_PageBreaks[page_nr - 1];
      }

      if(page_nr < static_cast<int>(m_PageBreaks.size()))
      {
        end_page_line = m_PageBreaks[page_nr];
      }
      else
      {
        end_page_line = m_refLayout->get_line_count();
      }

      //Get a Cairo Context, which is used as a drawing board:
      Cairo::RefPtr<Cairo::Context> cairo_ctx = print_context->get_cairo_context();

      //We'll use black letters:
      cairo_ctx->set_source_rgb(0, 0, 0);

      //Render Pango LayoutLines over the Cairo context:
      auto iter = m_refLayout->get_iter();

      double start_pos = 0;
      int line_index = 0;

      do
      {
        if(line_index >= start_page_line)
        {
          auto layout_line = iter.get_line();
          auto logical_rect = iter.get_line_logical_extents();
          int baseline = iter.get_baseline();

          if (line_index == start_page_line)
          {
            start_pos = logical_rect.get_y() / 1024.0;
          }

          cairo_ctx->move_to(logical_rect.get_x() / 1024.0,
            baseline / 1024.0 - start_pos);

          layout_line->show_in_cairo_context(cairo_ctx);
        }

        line_index++;
      }
      while(line_index < end_page_line && iter.next_line());
    }

#### PrintDialog

The following example demonstrates how to print some input from a user interface using PrintDialog. The user interface is similar to the previous example.

Printing - PrintDialog

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class PrintFormDialog;

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow(const Glib::RefPtr<Gtk::Application>& app);
      ~ExampleWindow() override;

    protected:
      void build_main_menu(const Glib::RefPtr<Gtk::Application>& app);

      // Action signal handlers:
      void on_menu_file_new();
      void on_menu_file_print_setup();
      void on_menu_file_print();
      void on_menu_file_quit();

      // Printing-related objects:
      Glib::RefPtr<PrintFormDialog> m_refPrintFormDialog;

      // Child widgets:
      Gtk::Box m_VBox;
      Gtk::Grid m_Grid;

      Gtk::Label m_NameLabel;
      Gtk::Entry m_NameEntry;

      Gtk::Label m_SurnameLabel;
      Gtk::Entry m_SurnameEntry;

      Gtk::Label m_CommentsLabel;
      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::TextView m_TextView;

      Glib::RefPtr<Gtk::TextBuffer> m_refTextBuffer;

      Glib::RefPtr<Gtk::Builder> m_refBuilder;
    };
    #endif //GTKMM_EXAMPLEWINDOW_H

File: `printformdialog.h` (For use with gtkmm 4)

    #ifndef GTKMM_PRINT_FORM_DIALOG_H
    #define GTKMM_PRINT_FORM_DIALOG_H

    #include <gtkmm.h>
    #include <pangomm.h>
    #include <vector>

    #define HAS_PRINT_DIALOG GTKMM_CHECK_VERSION(4,13,1)

    #if HAS_PRINT_DIALOG
    // We derive our own class from PrintDialog,
    // so we can put the actual print implementation here.
    class PrintFormDialog : public Gtk::PrintDialog
    {
    public:
      static Glib::RefPtr<PrintFormDialog> create();
      virtual ~PrintFormDialog();

      void set_name(const Glib::ustring& name) { m_Name = name; }
      void set_comments(const Glib::ustring& comments) { m_Comments = comments; }
      void do_setup(Gtk::Window* parent);
      void do_print(Gtk::Window* parent);

    protected:
      PrintFormDialog();

      // PrintDialog callback slots:
      void on_setup_finish(const Glib::RefPtr<Gio::AsyncResult>& result);
      void on_print_finish(const Glib::RefPtr<Gio::AsyncResult>& result);
      Cairo::ErrorStatus write_func(const unsigned char* data, unsigned int length,
        Glib::RefPtr<Gio::OutputStream>& stream);
      void do_printing(const Cairo::RefPtr<Cairo::Context>& cairo_ctx);

      Glib::ustring m_Name;
      Glib::ustring m_Comments;
      Glib::RefPtr<Pango::Layout> m_refLayout;
      Glib::RefPtr<Gtk::PrintSetup> m_refPrintSetup;
    };
    #endif // HAS_PRINT_DIALOG

    #endif // GTKMM_PRINT_FORM_DIALOG_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include "printformdialog.h"
    #include <iostream>

    ExampleWindow::ExampleWindow(const Glib::RefPtr<Gtk::Application>& app)
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_NameLabel("Name"),
      m_SurnameLabel("Surname"),
      m_CommentsLabel("Comments")
    {
      set_title("gtkmm PrintDialog Example");
      set_default_size(400, 300);

    #if HAS_PRINT_DIALOG
      // Create a PrintDialog. (We use our derived PrintDialog class.)
      m_refPrintFormDialog = PrintFormDialog::create();
    #endif // HAS_PRINT_DIALOG

      set_child(m_VBox);

      build_main_menu(app);

      m_VBox.append(m_Grid);

      // Arrange the widgets inside the grid:
      m_Grid.set_expand(true);
      m_Grid.set_row_spacing(5);
      m_Grid.set_column_spacing(5);
      m_Grid.attach(m_NameLabel, 0, 0);
      m_Grid.attach(m_NameEntry, 1, 0);

      m_Grid.attach(m_SurnameLabel, 0, 1);
      m_Grid.attach(m_SurnameEntry, 1, 1);

      // Add the TextView, inside a ScrolledWindow:
      m_ScrolledWindow.set_child(m_TextView);

      // Only show the scrollbars when they are necessary:
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);

      m_Grid.attach(m_CommentsLabel, 0, 2);
      m_Grid.attach(m_ScrolledWindow, 1, 2);
      m_ScrolledWindow.set_expand(true);

      m_refTextBuffer = Gtk::TextBuffer::create();
      m_TextView.set_buffer(m_refTextBuffer);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::build_main_menu(const Glib::RefPtr<Gtk::Application>& app)
    {
      // Create actions for menus and toolbars:
      auto refActionGroup = Gio::SimpleActionGroup::create();

      // File menu:
      refActionGroup->add_action("new",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_new));

      refActionGroup->add_action("printsetup",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_print_setup));

      refActionGroup->add_action("print",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_print));

      refActionGroup->add_action("quit",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_quit));

      insert_action_group("example", refActionGroup);

      // When the menubar is a child of a Gtk::Window, keyboard accelerators are not
      // automatically fetched from the Gio::Menu.
      // See the examples/book/menus/main_menu example for an alternative way of
      // adding the menubar when using Gtk::ApplicationWindow.
      app->set_accel_for_action("example.new", "<Primary>n");
      app->set_accel_for_action("example.print", "<Primary>p");
      app->set_accel_for_action("example.quit", "<Primary>q");

      m_refBuilder = Gtk::Builder::create();

      // Layout the actions in a menubar:
      Glib::ustring ui_menu_info =
        "<interface>"
        "  <menu id='menu-example'>"
        "    <submenu>"
        "      <attribute name='label' translatable='yes'>_File</attribute>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_New</attribute>"
        "          <attribute name='action'>example.new</attribute>"
        "        </item>"
        "      </section>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>Print _Setup...</attribute>"
        "          <attribute name='action'>example.printsetup</attribute>"
        "        </item>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_Print...</attribute>"
        "          <attribute name='action'>example.print</attribute>"
        "        </item>"
        "      </section>"
        "      <section>"
        "        <item>"
        "          <attribute name='label' translatable='yes'>_Quit</attribute>"
        "          <attribute name='action'>example.quit</attribute>"
        "        </item>"
        "      </section>"
        "    </submenu>"
        "  </menu>"
        "</interface>";

      try
      {
        m_refBuilder->add_from_string(ui_menu_info);
      }
      catch(const Glib::Error& ex)
      {
        std::cerr << "building menus failed: " << ex.what();
      }

      // Layout the actions in a toolbar:
      Glib::ustring ui_toolbar_info =
        "<!-- Generated with glade 3.18.3 and then changed manually -->"
        "<interface>"
          "<object class='GtkBox' id='toolbar'>"
            "<property name='can_focus'>False</property>"
            "<property name='spacing'>3</property>"
            "<child>"
              "<object class='GtkButton' id='toolbutton_new'>"
                "<property name='can_focus'>False</property>"
                "<property name='tooltip_text' translatable='yes'>New</property>"
                "<property name='action_name'>example.new</property>"
                "<property name='icon_name'>document-new</property>"
                "<property name='hexpand'>False</property>"
                "<property name='vexpand'>False</property>"
              "</object>"
            "</child>"
            "<child>"
              "<object class='GtkButton' id='toolbutton_print'>"
                "<property name='can_focus'>False</property>"
                "<property name='tooltip_text' translatable='yes'>Print</property>"
                "<property name='action_name'>example.print</property>"
                "<property name='icon_name'>document-print</property>"
                "<property name='hexpand'>False</property>"
                "<property name='vexpand'>False</property>"
              "</object>"
            "</child>"
            "<child>"
              "<object class='GtkSeparator' id='separator1'>"
                "<property name='can_focus'>False</property>"
                "<property name='hexpand'>False</property>"
                "<property name='vexpand'>False</property>"
              "</object>"
            "</child>"
            "<child>"
              "<object class='GtkButton' id='toolbutton_quit'>"
                "<property name='can_focus'>False</property>"
                "<property name='tooltip_text' translatable='yes'>Quit</property>"
                "<property name='action_name'>example.quit</property>"
                "<property name='icon_name'>application-exit</property>"
                "<property name='hexpand'>False</property>"
                "<property name='vexpand'>False</property>"
              "</object>"
            "</child>"
          "</object>"
        "</interface>";

      try
      {
        m_refBuilder->add_from_string(ui_toolbar_info);
      }
      catch(const Glib::Error& ex)
      {
        std::cerr << "building toolbar failed: " << ex.what();
      }

      // Get the menubar and add it to a container widget:
      auto object = m_refBuilder->get_object("menu-example");
      auto gmenu = std::dynamic_pointer_cast<Gio::Menu>(object);
      if (!gmenu)
        g_warning("GMenu not found");
      else
      {
        auto pMenuBar = Gtk::make_managed<Gtk::PopoverMenuBar>(gmenu);

        // Add the PopoverMenuBar to the window:
        m_VBox.append(*pMenuBar);
      }

      // Get the toolbar and add it to a container widget:
      auto toolbar = m_refBuilder->get_widget<Gtk::Box>("toolbar");
      if (!toolbar)
        g_warning("toolbar not found");
      else
        m_VBox.append(*toolbar);
    }

    void ExampleWindow::on_menu_file_new()
    {
      // Clear entries and textview:
      m_NameEntry.set_text("");
      m_SurnameEntry.set_text("");
      m_refTextBuffer->set_text("");
      m_TextView.set_buffer(m_refTextBuffer);
    }

    void ExampleWindow::on_menu_file_print_setup()
    {
    #if HAS_PRINT_DIALOG
      m_refPrintFormDialog->do_setup(this);
    #else
      std::cout << "Gtk::PrintDialog is not available.\n";
    #endif // HAS_PRINT_DIALOG
    }

    void ExampleWindow::on_menu_file_print()
    {
    #if HAS_PRINT_DIALOG
      m_refPrintFormDialog->set_name(m_NameEntry.get_text() + " " + m_SurnameEntry.get_text());
      m_refPrintFormDialog->set_comments(m_refTextBuffer->get_text(false /*Don't include hidden*/));
      m_refPrintFormDialog->do_print(this);
    #else
      std::cout << "Gtk::PrintDialog is not available.\n";
    #endif // HAS_PRINT_DIALOG
    }

    void ExampleWindow::on_menu_file_quit()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv, app);
    }

File: `printformdialog.cc` (For use with gtkmm 4)

    #include "printformdialog.h"
    #include <iostream>

    #if HAS_PRINT_DIALOG
    PrintFormDialog::PrintFormDialog()
    {
      set_page_setup(Gtk::PageSetup::create());
      set_print_settings(Gtk::PrintSettings::create());
    }

    PrintFormDialog::~PrintFormDialog()
    {
    }

    Glib::RefPtr<PrintFormDialog> PrintFormDialog::create()
    {
      return Glib::make_refptr_for_instance<PrintFormDialog>(new PrintFormDialog());
    }

    void PrintFormDialog::do_setup(Gtk::Window* parent)
    {
      set_title("Print setup");
      if (parent)
        setup(*parent, sigc::mem_fun(*this, &PrintFormDialog::on_setup_finish));
      else
        setup(sigc::mem_fun(*this, &PrintFormDialog::on_setup_finish));
    }

    void PrintFormDialog::do_print(Gtk::Window* parent)
    {
      set_title("Printing");
      if (parent)
        print(*parent, sigc::mem_fun(*this, &PrintFormDialog::on_print_finish));
      else
        print(sigc::mem_fun(*this, &PrintFormDialog::on_print_finish));
    }

    void PrintFormDialog::on_setup_finish(const Glib::RefPtr<Gio::AsyncResult>& result)
    {
      try
      {
        m_refPrintSetup = setup_finish(result);
        if (m_refPrintSetup)
        {
          set_page_setup(m_refPrintSetup->get_page_setup());
          set_print_settings(m_refPrintSetup->get_print_settings());
        }
      }
      catch (const Gtk::DialogError& err)
      {
        // Can be thrown by setup_finish(result).
        std::cout << "No setup selected. " << err.what() << std::endl;
      }
      catch (const Glib::Error& err)
      {
        std::cout << "Unexpected exception. " << err.what() << std::endl;
      }
    }

    void PrintFormDialog::on_print_finish(const Glib::RefPtr<Gio::AsyncResult>& result)
    {
      Glib::RefPtr<Gio::OutputStream> outputStream;
      try
      {
        outputStream = print_finish(result);
      }
      catch (const Gtk::DialogError& err)
      {
        // Can be thrown by print_finish(result).
        std::cout << "No output stream. " << err.what() << std::endl;
        return;
      }
      catch (const Glib::Error& err)
      {
        std::cout << "Unexpected exception. " << err.what() << std::endl;
        return;
      }
      const double paper_width = get_page_setup()->get_paper_width(Gtk::Unit::POINTS);
      const double paper_height = get_page_setup()->get_paper_height(Gtk::Unit::POINTS);
      auto cairo_surface = Cairo::PdfSurface::create_for_stream(
        sigc::bind(sigc::mem_fun(*this, &PrintFormDialog::write_func), outputStream),
        paper_width, paper_height);
      auto cairo_ctx = Cairo::Context::create(cairo_surface);

      do_printing(cairo_ctx);

      // cairo_surface->finish() calls write_func(),
      // which must be done before the stream is closed.
      cairo_surface->finish();
      try
      {
        outputStream->close();
      }
      catch (const Glib::Error& err)
      {
        std::cout << "Error closing stream. " << err.what() << std::endl;
      }
    }

    Cairo::ErrorStatus PrintFormDialog::write_func(const unsigned char* data,
      unsigned int length, Glib::RefPtr<Gio::OutputStream>& stream)
    {
      try
      {
        gsize bytes_written = 0;
        stream->write_all(data, length, bytes_written);
      }
      catch (const Glib::Error& err)
      {
        std::cout << "Error writing to stream. " << err.what() << std::endl;
        return CAIRO_STATUS_WRITE_ERROR;
      }
      return CAIRO_STATUS_SUCCESS;
    }
    void PrintFormDialog::do_printing(const Cairo::RefPtr<Cairo::Context>& cairo_ctx)
    {
      m_refLayout = Pango::Layout::create(cairo_ctx);
      m_refLayout->set_font_description(Pango::FontDescription("sans 12"));

      const auto page_setup = get_page_setup();
      const double page_width = page_setup->get_page_width(Gtk::Unit::POINTS);
      const double page_height = page_setup->get_page_height(Gtk::Unit::POINTS);
      const double left_margin = page_setup->get_left_margin(Gtk::Unit::POINTS);
      const double top_margin = page_setup->get_top_margin(Gtk::Unit::POINTS);
      m_refLayout->set_width(static_cast<int>(page_width * Pango::SCALE));
      m_refLayout->set_wrap(Pango::WrapMode::WORD_CHAR);
      cairo_ctx->translate(left_margin, top_margin);

      // Set and mark up the text to print:
      Glib::ustring marked_up_form_text =
        "<b>Name</b>: " + m_Name + "\n\n" +
        "<b>Comments</b>: " + m_Comments;
      m_refLayout->set_markup(marked_up_form_text);

      // We'll use black letters:
      cairo_ctx->set_source_rgb(0, 0, 0);

      // Render Pango LayoutLines over the Cairo context:
      const double inverse_pango_scale = 1.0 / Pango::SCALE;
      double page_y = 0.0;
      auto iter = m_refLayout->get_iter();
      double start_y_pos = iter.get_line_logical_extents().get_y() * inverse_pango_scale;
      do
      {
        const auto layout_line = iter.get_line();
        const auto logical_rect = iter.get_line_logical_extents();
        const double line_height = logical_rect.get_height() * inverse_pango_scale;

        if (page_y + line_height > page_height)
        {
          // Start a new page.
          cairo_ctx->show_page();
          page_y = 0.0;
          start_y_pos = logical_rect.get_y() * inverse_pango_scale;
        }
        page_y += line_height;

        cairo_ctx->move_to(logical_rect.get_x() * inverse_pango_scale,
          iter.get_baseline() * inverse_pango_scale - start_y_pos);
        layout_line->show_in_cairo_context(cairo_ctx);
      }
      while (iter.next_line());

      cairo_ctx->show_page();
    }
    #endif // HAS_PRINT_DIALOG

## Documentos usados recentemente

gtkmm provides an easy way to manage recently used documents. This functionality is implemented in the Gtk::RecentManager class.

Each item in the list of recently used files is identified by its URI, and can have associated metadata. The metadata can be used to specify how the file should be displayed, a description of the file, its mime type, which application registered it, whether it's private to the registering application, and several other things.

### RecentManager

RecentManager acts as a database of recently used files. You use this class to register new files, remove files from the list, or look up recently used files. There is one list of recently used files per user.

You can create a new RecentManager, but you'll most likely just want to use the default one. You can get a reference to the default RecentManager with get_default().

#### Adding Items to the List of Recent Files

To add a new file to the list of recent documents, in the simplest case, you only need to provide the URI. For example:

    auto recent_manager = Gtk::RecentManager::get_default();
    recent_manager->add_item(uri);

If you want to register a file with metadata, you can pass a RecentManager::Data parameter to add_item(). The metadata that can be set on a particular file item is as follows:

- `app_exec`: The command line to be used to launch this resource. This string may contain the "f" and "u" escape characters which will be expanded to the resource file path and URI respectively

- `app_name`: The name of the application that registered the resource

- `description`: A short description of the resource as a UTF-8 encoded string

- `display_name`: The name of the resource to be used for display as a UTF-8 encoded string

- `groups`: A list of groups associated with this item. Groups are essentially arbitrary strings associated with a particular resource. They can be thought of as 'categories' (such as "email", "graphics", etc) or tags for the resource.

- `is_private`: Whether this resource should be visible only to applications that have registered it or not

- `mime_type`: O tipo MIME do recurso

In addition to adding items to the list, you can also look up items from the list and modify or remove items.

#### Looking up Items in the List of Recent Files

To look up recently used files, RecentManager provides several functions. To look up a specific item by its URI, you can use the lookup_item() function, which will return a RecentInfo class. If the specified URI did not exist in the list of recent files, lookup_item() throws a RecentManagerError exception. For example:

    Glib::RefPtr<Gtk::RecentInfo> info;
    try
    {
      info = recent_manager->lookup_item(uri);
    }
    catch(const Gtk::RecentManagerError& ex)
    {
      std::cerr << "RecentManagerError: " << ex.what() << std::endl;
    }
    if (info)
    {
      // item was found
    }

A RecentInfo object is essentially an object containing all of the metadata about a single recently-used file. You can use this object to look up any of the properties listed above.

If you don't want to look for a specific URI, but instead want to get a list of all recently used items, RecentManager provides the get_items() function. The return value of this function is a std::vector of all recently used files. The following code demonstrates how you might get a list of recently used files:

    auto info_list = recent_manager->get_items();

The maximum age of items in the recently used files list can be set with Gtk::Settings::property_gtk_recent_files_max_age(). Default value: 30 days.

#### Modificando a lista de arquivos recentes

There may be times when you need to modify the list of recent files. For instance, if a file is moved or renamed, you may need to update the file's location in the recent files list so that it doesn't point to an incorrect location. You can update an item's location by using move_item().

In addition to changing a file's URI, you can also remove items from the list, either one at a time or by clearing them all at once. The former is accomplished with remove_item(), the latter with purge_items().

The functions move_item(), remove_item() and purge_items() have no effect on the actual files that are referred to by the URIs, they only modify the list of recent files.

### FileChooser and FileDialog

FileChooser is an interface that can be implemented by widgets displaying a list of files. gtkmm provides three built-in implementations for choosing recent files or other files: FileChooserWidget, FileChooserDialog, and FileChooserNative.

FileChooserWidget is a simple widget for displaying a list of recently used files or other files. FileChooserWidget is the basic building block for FileChooserDialog, but you can embed it into your user interface if you want to.

FileChooser and the classes that implement it are deprecated since gtkmm 4.10. They have been replaced by FileDialog, which is available since gtkmm 4.10.

#### Simple FileDialog example

Shown below is a simple example of how to use the FileDialog class in a program. This simple program has a menubar with a File Dialog menu item. When you select this menu item, a dialog pops up showing a list of files. If you select Recent in the sidebar, the list of recently used files is shown.

If this is the first time you're using a program that uses the Recent Files framework, the dialog may be empty at first. Otherwise it should show the list of recently used documents registered by other applications.

After selecting the File Dialog menu item and the Recent sidebar item, you should see something similar to the following window.

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow(const Glib::RefPtr<Gtk::Application>& app);
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_menu_file_files_dialog();
      void on_menu_file_quit();
      void on_menu_file_new();
      void on_dialog_finish(Glib::RefPtr<Gio::AsyncResult>& result);

      //Child widgets:
      Gtk::Box m_Box;

      Glib::RefPtr<Gtk::Builder> m_refBuilder;
      Glib::RefPtr<Gio::SimpleActionGroup> m_refActionGroup;

      Glib::RefPtr<Gtk::RecentManager> m_refRecentManager;
      Glib::RefPtr<Gtk::FileDialog> m_refFileDialog;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow(const Glib::RefPtr<Gtk::Application>& app)
    : m_Box(Gtk::Orientation::VERTICAL),
      m_refRecentManager(Gtk::RecentManager::get_default())
    {
      set_title("Recent files example");
      set_default_size(300, 150);

      //We can put a PopoverMenuBar at the top of the box and other stuff below it.
      set_child(m_Box);

      //Create actions for menus and toolbars:
      m_refActionGroup = Gio::SimpleActionGroup::create();

      //File menu:
      m_refActionGroup->add_action("new",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_new));

      //A menu item to open the file dialog:
      m_refActionGroup->add_action("files-dialog",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_files_dialog));

      m_refActionGroup->add_action("quit",
        sigc::mem_fun(*this, &ExampleWindow::on_menu_file_quit) );

      insert_action_group("example", m_refActionGroup);

      m_refBuilder = Gtk::Builder::create();

      // When the menubar is a child of a Gtk::Window, keyboard accelerators are not
      // automatically fetched from the Gio::Menu.
      // See the examples/book/menus/main_menu example for an alternative way of
      // adding the menubar when using Gtk::ApplicationWindow.
      app->set_accel_for_action("example.new", "<Primary>n");
      app->set_accel_for_action("example.files-dialog", "<Primary>o");
      app->set_accel_for_action("example.quit", "<Primary>q");

      //Layout the actions in a menubar and a toolbar:
      const char* ui_info =
        "<interface>"
        "  <menu id='menubar'>"
        "    <submenu>"
        "      <attribute name='label' translatable='yes'>_File</attribute>"
        "      <item>"
        "        <attribute name='label' translatable='yes'>_New</attribute>"
        "        <attribute name='action'>example.new</attribute>"
        "        <attribute name='accel'>&lt;Primary&gt;n</attribute>"
        "      </item>"
        "      <item>"
        "        <attribute name='label' translatable='yes'>File _Dialog</attribute>"
        "        <attribute name='action'>example.files-dialog</attribute>"
        "        <attribute name='accel'>&lt;Primary&gt;o</attribute>"
        "      </item>"
        "      <item>"
        "        <attribute name='label' translatable='yes'>_Quit</attribute>"
        "        <attribute name='action'>example.quit</attribute>"
        "        <attribute name='accel'>&lt;Primary&gt;q</attribute>"
        "      </item>"
        "    </submenu>"
        "  </menu>"
        "  <object class='GtkBox' id='toolbar'>"
        "    <property name='can_focus'>False</property>"
        "    <child>"
        "      <object class='GtkButton' id='toolbutton_new'>"
        "        <property name='can_focus'>False</property>"
        "        <property name='tooltip_text' translatable='yes'>New</property>"
        "        <property name='action_name'>example.new</property>"
        "        <property name='icon_name'>document-new</property>"
        "        <property name='hexpand'>False</property>"
        "        <property name='vexpand'>False</property>"
        "      </object>"
        "    </child>"
        "    <child>"
        "      <object class='GtkButton' id='toolbutton_quit'>"
        "        <property name='can_focus'>False</property>"
        "        <property name='tooltip_text' translatable='yes'>Quit</property>"
        "        <property name='action_name'>example.quit</property>"
        "        <property name='icon_name'>application-exit</property>"
        "        <property name='hexpand'>False</property>"
        "        <property name='vexpand'>False</property>"
        "      </object>"
        "    </child>"
        "  </object>"
        "</interface>";

      try
      {
        m_refBuilder->add_from_string(ui_info);
      }
      catch(const Glib::Error& ex)
      {
        std::cerr << "building menubar and toolbar failed: " <<  ex.what();
      }

      //Get the menubar and toolbar widgets, and add them to a container widget:
      auto object = m_refBuilder->get_object("menubar");
      auto gmenu = std::dynamic_pointer_cast<Gio::Menu>(object);
      if (gmenu)
      {
        //Menubar:
        auto pMenubar = Gtk::make_managed<Gtk::PopoverMenuBar>(gmenu);
        m_Box.append(*pMenubar);
      }
      else
        g_warning("GMenu not found");

      auto pToolbar = m_refBuilder->get_widget<Gtk::Box>("toolbar");
      if (pToolbar)
        //Toolbar:
        m_Box.append(*pToolbar);
      else
        g_warning("toolbar not found");
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_menu_file_new()
    {
      std::cout << " New File" << std::endl;
    }

    void ExampleWindow::on_menu_file_quit()
    {
      close(); // Closes the main window to stop the app->make_window_and_run().
    }

    void ExampleWindow::on_menu_file_files_dialog()
    {
      if (!m_refFileDialog)
      {
        m_refFileDialog = Gtk::FileDialog::create();
        m_refFileDialog->set_modal(true);
      }
      m_refFileDialog->open(*this, sigc::mem_fun(*this, &ExampleWindow::on_dialog_finish));
    }

    void ExampleWindow::on_dialog_finish(Glib::RefPtr<Gio::AsyncResult>& result)
    {
      Glib::RefPtr<Gio::File> file;
      try
      {
        file = m_refFileDialog->open_finish(result);
      }
      catch (const Gtk::DialogError& err)
      {
        std::cout << "No file selected, " << err.what() << std::endl;
        return;
      }

      auto selected_uri = file->get_uri();
      std::cout << "URI selected = " << selected_uri << std::endl;
      std::cout << (m_refRecentManager->has_item(selected_uri) ? "A" : "Not a")
        << " recently used file" << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv, app);
    }

The constructor for ExampleWindow creates the menu and the toolbar using Builder (see for more information). It then adds the menu and the toolbar to the window.

#### Filtering Files

For any of the FileChooser classes, if you don't wish to display all of the items in the list of files, you can filter the list to show only those that you want. You can filter the list with the help of the FileFilter class. This class allows you to filter files by their name (add_pattern()), or their mime type (add_mime_type()).

After you've created and set up the filter to match only the items you want, you can apply a filter to a chooser widget with the FileChooser::add_filter() function.

## Keyboard and Mouse Events

Event signals differ in some ways from other signals. These differences are described in the Event signals section in the appendix. Here we will use keyboard events and mouse events to show how events can be used in a program.

### Visão geral

Whenever you press or release a key, an event is emitted. You can add an event controller and connect a signal handler to handle such events.

The event signal handler will receive arguments that depend on the type of event. For key press events the arguments are (guint `keyval`, guint `keycode`, Gdk::ModifierType `state`). As described in the appendix, the key press event signal handler returns a bool value, to indicate that the signal is fully handled (`true`) or allow event propagation (`false`).

To determine which key was pressed or released, you read the value of the `keyval` argument and compare it with a constant in the `<gdk/gdkkeysyms.h>` header file. The states of modifier keys (shift, ctrl, etc.) are available as bit-flags in `state`.

Here's a simple example:

    bool MyClass::on_key_pressed(guint keyval, guint, Gdk::ModifierType state)
    {
      if (keyval == GDK_KEY_1 &&
        (state & (Gdk::ModifierType::SHIFT_MASK | Gdk::ModifierType::CONTROL_MASK |
         Gdk::ModifierType::ALT_MASK)) == Gdk::ModifierType::ALT_MASK)
      {
        handle_alt_press();
        return true;
      }
      return false;
    }

    // in MyClass constructor
    auto controller = Gtk::EventControllerKey::create();
    controller->signal_key_pressed().connect(
      sigc::mem_fun(*this, &MyClass::on_key_pressed), false);
    add_controller(controller);

#### Exemplo

In this example there are three keyboard shortcuts: Alt+1 selects the first radio button, Alt+2 selects the second one, and the Esc key closes the window.

Eventos de teclado - Simples

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:

      ExampleWindow();
      virtual ~ExampleWindow();

    private:
      // Signal handler:
      bool on_window_key_pressed(guint keyval, guint keycode, Gdk::ModifierType state);

      Gtk::Box m_container;
      Gtk::CheckButton m_first;
      Gtk::CheckButton m_second;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    {
      set_title("Keyboard Events");
      m_container.set_margin(10);
      set_child(m_container);

      // Radio buttons:
      m_first.set_label("First");
      m_second.set_label("Second");

      m_second.set_group(m_first);
      m_first.set_active();

      // Main Container:
      m_container.set_orientation(Gtk::Orientation::HORIZONTAL);
      m_container.append(m_first);
      m_container.append(m_second);

      // Events.
      auto controller = Gtk::EventControllerKey::create();
      controller->signal_key_pressed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_window_key_pressed), false);
      add_controller(controller);
    }

    bool ExampleWindow::on_window_key_pressed(guint keyval, guint, Gdk::ModifierType state)
    {
      //Gdk::ModifierType::ALT_MASK -> the 'Alt' key(mask)
      //GDK_KEY_1 -> the '1' key
      //GDK_KEY_2 -> the '2' key

      //select the first radio button, when we press alt + 1
      if((keyval == GDK_KEY_1) &&
        (state & (Gdk::ModifierType::SHIFT_MASK | Gdk::ModifierType::CONTROL_MASK | Gdk::ModifierType::ALT_MASK)) == Gdk::ModifierType::ALT_MASK)
      {
        m_first.set_active();
        //returning true, cancels the propagation of the event
        return true;
      }
      else if((keyval == GDK_KEY_2) &&
        (state & (Gdk::ModifierType::SHIFT_MASK | Gdk::ModifierType::CONTROL_MASK | Gdk::ModifierType::ALT_MASK)) == Gdk::ModifierType::ALT_MASK)
      {
        //and the second radio button, when we press alt + 2
        m_second.set_active();
        return true;
      }
      else if(keyval == GDK_KEY_Escape)
      {
        //close the window, when the 'esc' key is pressed
        close();
        return true;
      }

      //the event has not been handled
      return false;
    }

    ExampleWindow::~ExampleWindow()
    {
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Propagação de eventos

As described in the appendix event signals are propagated in 3 phases:

1. Capture phase - runs from the toplevel down to the event widget.

2. Target phase - runs only on the event widget.

3. Bubble phase - runs from the event widget up to the toplevel.

A keyboard event is first sent to the toplevel window (Gtk::Window), where it will be checked for any keyboard shortcuts that may be set (accelerator keys and mnemonics, used for selecting menu items from the keyboard). After this (and assuming the event wasn't handled), it is propagated down until it reaches the widget which has keyboard focus. The event will then propagate up until it reaches the top-level widget, or until you stop the propagation by returning `true` from an event handler.

Notice, that after canceling an event, no other function will be called (even if it is from the same widget).

#### Exemplo

In this example there are 9 EventControllerKeys, 3 in each of a Gtk::Window, a Gtk::Box and a Gtk::Label. In each of the widgets there is one event controller for each propagation phase.

The purpose of this example is to show the steps the event takes when it is emitted.

When you write in the label, a key press event will be emitted, which will go first, in the capture phase, to the toplevel window (Gtk::Window), then down to its child, the box, then to the box's child, the label with the keyboard focus. In the target phase the event goes only to the widget with the keyboard focus (the label). In the bubble phase the event goes first to the widget with the keyboard focus (the label), then to its parent (the box), then to the box's parent (the window). If the event propagates all the way down to the label and then up to the window without being stopped, the text you're writing will appear in the Label above the Label you're writing in.

Eventos de teclado - Propagação de eventos

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EVENT_PROPAGATION_H
    #define GTKMM_EVENT_PROPAGATION_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:

      ExampleWindow();
      ~ExampleWindow() override;

    private:
      // Signal handlers:
      bool label2_key_pressed(guint keyval, guint keycode, Gdk::ModifierType state, const Glib::ustring& phase);
      bool box_key_pressed(guint keyval, guint keycode, Gdk::ModifierType state, const Glib::ustring& phase);
      bool window_key_pressed(guint keyval, guint keycode, Gdk::ModifierType state, const Glib::ustring& phase);

      bool m_first = true;
      Gtk::Box m_container;
      Gtk::Frame m_frame;
      Gtk::Label m_label1 {"A label"};
      Gtk::Label m_label2 {"Write here"};
      Gtk::CheckButton m_checkbutton_can_propagate_down {"Can propagate down in the capture phase"};
      Gtk::CheckButton m_checkbutton_can_propagate_up {"Can propagate up in the bubble phase"};
    };

    #endif //GTKMM_EVENT_PROPAGATION_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow()
    {
      set_title("Event Propagation");
      m_container.set_margin(10);
      set_child(m_container);

      m_frame.set_child(m_label2);
      m_label2.set_selectable();
      m_checkbutton_can_propagate_down.set_active();
      m_checkbutton_can_propagate_up.set_active();

      // Main container
      m_container.set_orientation(Gtk::Orientation::VERTICAL);
      m_container.append(m_label1);
      m_container.append(m_frame);
      m_container.append(m_checkbutton_can_propagate_down);
      m_container.append(m_checkbutton_can_propagate_up);

      // Event controllers
      const bool after = false; // Run before or after the default signal handlers.

      // Called in the capture phase of the event handling.
      auto controller = Gtk::EventControllerKey::create();
      controller->set_propagation_phase(Gtk::PropagationPhase::CAPTURE);
      controller->signal_key_pressed().connect(
        sigc::bind(sigc::mem_fun(*this, &ExampleWindow::label2_key_pressed), "capture"), after);
      m_label2.add_controller(controller);

      controller = Gtk::EventControllerKey::create();
      controller->set_propagation_phase(Gtk::PropagationPhase::CAPTURE);
      controller->signal_key_pressed().connect(
        sigc::bind(sigc::mem_fun(*this, &ExampleWindow::box_key_pressed), "capture"), after);
      m_container.add_controller(controller);

      controller = Gtk::EventControllerKey::create();
      controller->set_propagation_phase(Gtk::PropagationPhase::CAPTURE);
      controller->signal_key_pressed().connect(
        sigc::bind(sigc::mem_fun(*this, &ExampleWindow::window_key_pressed), "capture"), after);
      add_controller(controller);

      // Called in the target phase of the event handling.
      controller = Gtk::EventControllerKey::create();
      controller->set_propagation_phase(Gtk::PropagationPhase::TARGET);
      controller->signal_key_pressed().connect(
        sigc::bind(sigc::mem_fun(*this, &ExampleWindow::label2_key_pressed), "target"), after);
      m_label2.add_controller(controller);

      controller = Gtk::EventControllerKey::create();
      controller->set_propagation_phase(Gtk::PropagationPhase::TARGET);
      controller->signal_key_pressed().connect(
        sigc::bind(sigc::mem_fun(*this, &ExampleWindow::box_key_pressed), "target"), after);
      m_container.add_controller(controller);

      controller = Gtk::EventControllerKey::create();
      controller->set_propagation_phase(Gtk::PropagationPhase::TARGET);
      controller->signal_key_pressed().connect(
        sigc::bind(sigc::mem_fun(*this, &ExampleWindow::window_key_pressed), "target"), after);
      add_controller(controller);

      // Called in the bubble phase of the event handling.
      // This is the default, if set_propagation_phase() is not called.
      controller = Gtk::EventControllerKey::create();
      controller->set_propagation_phase(Gtk::PropagationPhase::BUBBLE);
      controller->signal_key_pressed().connect(
        sigc::bind(sigc::mem_fun(*this, &ExampleWindow::label2_key_pressed), "bubble"), after);
      m_label2.add_controller(controller);

      controller = Gtk::EventControllerKey::create();
      controller->set_propagation_phase(Gtk::PropagationPhase::BUBBLE);
      controller->signal_key_pressed().connect(
        sigc::bind(sigc::mem_fun(*this, &ExampleWindow::box_key_pressed), "bubble"), after);
      m_container.add_controller(controller);

      controller = Gtk::EventControllerKey::create();
      controller->set_propagation_phase(Gtk::PropagationPhase::BUBBLE);
      controller->signal_key_pressed().connect(
        sigc::bind(sigc::mem_fun(*this, &ExampleWindow::window_key_pressed), "bubble"), after);
      add_controller(controller);
    }

    // By changing the return value we allow, or don't allow, the event to propagate to other elements.
    bool ExampleWindow::label2_key_pressed(guint keyval, guint, Gdk::ModifierType, const Glib::ustring& phase)
    {
      std::cout << "Label,  " << phase << " phase" << std::endl;

      if (phase == "bubble")
      {
        const gunichar unichar = gdk_keyval_to_unicode(keyval);
        if (unichar != 0)
        {
          if (m_first)
          {
            m_label2.set_label("");
            m_first = false;
          }
          if (unichar == '\b')
            m_label2.set_label("");
          else
          {
            const Glib::ustring newchar(1, unichar);
            m_label2.set_label(m_label2.get_label() + newchar);
          }
        }

        if (!m_checkbutton_can_propagate_up.get_active())
          return true; // Don't propagate
      }
      return false;
    }

    bool ExampleWindow::box_key_pressed(guint, guint, Gdk::ModifierType, const Glib::ustring& phase)
    {
      std::cout << "Box,    " << phase << " phase" << std::endl;

      // Let it propagate
      return false;
    }

    // This will set the second label's text in the first label every time a key is pressed.
    bool ExampleWindow::window_key_pressed(guint, guint, Gdk::ModifierType, const Glib::ustring& phase)
    {
      if (phase == "capture")
        std::cout << std::endl;
      std::cout << "Window, " << phase << " phase";

      // Checking if the second label is on focus, otherwise the label would get
      // changed by pressing keys on the window (when the label is not on focus),
      // even if m_checkbutton_can_propagate_up wasn't active.
      if (phase == "bubble" && m_label2.has_focus())
      {
        m_label1.set_label(m_label2.get_label());
        std::cout << ", " << m_label2.get_label();
      }
      std::cout << std::endl;

      if (phase == "capture" && !m_checkbutton_can_propagate_down.get_active())
        return true; // Don't propagate
      return false;
    }

    ExampleWindow::~ExampleWindow()
    {
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

### Mouse Events

Mouse events are similar to keyboard events. There are some differences, though.

- You use Gtk::GestureClick instead of Gtk::EventControllerKey.

- There are other event classes that can be used for handling mouse events, for instance Gtk::EventControllerMotion and Gtk::EventControllerScroll.

- Many signal handlers don't return a `bool`. You can't stop those events from propagating.

The event classes that handle mouse events are also useful for handling events from touchscreens. There are also many subclasses of Gtk::EventController which are only (or mainly) useful for touchscreens. Examples: Gtk::GestureRotate, Gtk::GestureZoom, Gtk::GestureSwipe, Gtk::GestureLongPress.

Reference

#### Exemplo

This is an expanded version of the simple keyboard events example.

Keyboard and Mouse Events

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    private:
      // Signal handlers:
      void on_window_mouse_pressed(int n_press, double x, double y);
      void on_first_button_mouse_pressed(int n_press, double x, double y);
      void on_second_button_mouse_pressed(int n_press, double x, double y);
      void on_third_button_mouse_pressed(int n_press, double x, double y);
      void on_third_button_clicked();
      void on_mouse_released(int n_press, double x, double y);
      void on_mouse_motion(double x, double y);
      bool on_mouse_scroll(double dx, double dy);
      bool on_key_pressed(guint keyval, guint keycode, Gdk::ModifierType state);

      Gtk::Box m_box;
      Gtk::CheckButton m_first;
      Gtk::CheckButton m_second;
      Gtk::Button m_third;

      Glib::RefPtr<Gtk::GestureClick> m_window_click;
      Glib::RefPtr<Gtk::GestureClick> m_first_button_click;
      Glib::RefPtr<Gtk::GestureClick> m_second_button_click;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <map>
    #include <iostream>

    namespace
    {
    std::map<unsigned int, Glib::ustring> mouse_buttons
    {
      {0, "No button"},
      {GDK_BUTTON_PRIMARY, "Primary"},
      {GDK_BUTTON_MIDDLE, "Middle"},
      {GDK_BUTTON_SECONDARY, "Secondary"},
    };
    }

    ExampleWindow::ExampleWindow()
    : m_first("First"),
      m_second("Second"),
      m_third("Click me")
    {
      set_title("Keyboard and Mouse Events");
      m_box.set_margin(10);
      set_child(m_box);

      // Radio buttons
      m_second.set_group(m_first);
      m_first.set_active();

      // Main container
      m_box.set_orientation(Gtk::Orientation::HORIZONTAL);
      m_box.append(m_first);
      m_box.append(m_second);
      m_box.append(m_third);

      // Keyboard events
      auto key_controller = Gtk::EventControllerKey::create();
      key_controller->signal_key_pressed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_key_pressed), false);
      add_controller(key_controller);

      // Mouse events, window
      auto motion_controller = Gtk::EventControllerMotion::create();
      motion_controller->signal_motion().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_mouse_motion));
      add_controller(motion_controller);

      m_window_click = Gtk::GestureClick::create();
      m_window_click->set_button(0); // All mouse buttons
      m_window_click->signal_pressed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_window_mouse_pressed));
      add_controller(m_window_click);

      auto mouse_click = Gtk::GestureClick::create();
      mouse_click->set_button(GDK_BUTTON_PRIMARY);
      mouse_click->signal_released().connect(sigc::mem_fun(*this, &ExampleWindow::on_mouse_released));
      add_controller(mouse_click);

      auto mouse_scroll = Gtk::EventControllerScroll::create();
      mouse_scroll->set_flags(Gtk::EventControllerScroll::Flags::VERTICAL);
      // Handle mouse wheel rotations
      mouse_scroll->signal_scroll().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_mouse_scroll), true);
      add_controller(mouse_scroll);

      // Mouse events, buttons
      m_first_button_click = Gtk::GestureClick::create();
      m_first_button_click->set_button(GDK_BUTTON_PRIMARY);
      m_first_button_click->signal_pressed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_first_button_mouse_pressed));
      m_first.add_controller(m_first_button_click);

      m_second_button_click = Gtk::GestureClick::create();
      m_second_button_click->set_button(GDK_BUTTON_PRIMARY);
      m_second_button_click->signal_pressed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_second_button_mouse_pressed));
      m_second.add_controller(m_second_button_click);

      mouse_click = Gtk::GestureClick::create();
      // This mouse event must be handled in the capture phase.
      // The GtkButton C class handles the event in the capture phase and
      // does not let it propagate to the bubble phase where events are
      // handled by default.
      mouse_click->set_propagation_phase(Gtk::PropagationPhase::CAPTURE);
      mouse_click->set_button(GDK_BUTTON_PRIMARY);
      mouse_click->signal_pressed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_third_button_mouse_pressed));
      m_third.add_controller(mouse_click);
      m_third.signal_clicked().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_third_button_clicked));
    }

    void ExampleWindow::on_window_mouse_pressed(int n_press, double x, double y)
    {
      const auto current_button = mouse_buttons[m_window_click->get_current_button()];
      std::cout << "Mouse pressed in window: " << current_button
        << ", " << n_press << ", " << x << ", " << y << std::endl;
    }

    void ExampleWindow::on_first_button_mouse_pressed(int n_press, double x, double y)
    {
      const auto current_button = mouse_buttons[m_first_button_click->get_current_button()];
      std::cout << "Mouse pressed in first button: " << current_button
        << ", " << n_press << ", " << x << ", " << y << std::endl;
    }

    void ExampleWindow::on_second_button_mouse_pressed(int n_press, double x, double y)
    {
      const auto current_button = mouse_buttons[m_second_button_click->get_current_button()];
      std::cout << "Mouse pressed in second button: " << current_button
        << ", " << n_press << ", " << x << ", " << y << std::endl;
    }

    void ExampleWindow::on_third_button_mouse_pressed(int n_press, double x, double y)
    {
      std::cout << "Mouse pressed in third button: "
        << n_press << ", " << x << ", " << y << std::endl;
    }

    void ExampleWindow::on_third_button_clicked()
    {
      std::cout << "Third button clicked" << std::endl;
    }

    void ExampleWindow::on_mouse_released(int n_press, double x, double y)
    {
      std::cout << "Mouse released: " << n_press << ", " << x << ", " << y << std::endl;
    }

    void ExampleWindow::on_mouse_motion(double x, double y)
    {
      std::cout << "Mouse motion: "  << x << ", " << y << std::endl;
    }

    bool ExampleWindow::on_mouse_scroll(double dx, double dy)
    {
      std::cout << "Mouse scroll: "  << dx << ", " << dy << std::endl;
      return true; // handled
    }

    bool ExampleWindow::on_key_pressed(guint keyval, guint, Gdk::ModifierType state)
    {
      // Gdk::ModifierType::ALT_MASK -> the 'Alt' key(mask)
      // GDK_KEY_1 -> the '1' key
      // GDK_KEY_2 -> the '2' key

      // Select the first radio button, when we press Alt + 1
      if ((keyval == GDK_KEY_1) &&
        (state & (Gdk::ModifierType::SHIFT_MASK | Gdk::ModifierType::CONTROL_MASK | Gdk::ModifierType::ALT_MASK)) == Gdk::ModifierType::ALT_MASK)
      {
        m_first.set_active();
        // Returning true, cancels the propagation of the event
        return true;
      }
      else if ((keyval == GDK_KEY_2) &&
        (state & (Gdk::ModifierType::SHIFT_MASK | Gdk::ModifierType::CONTROL_MASK | Gdk::ModifierType::ALT_MASK)) == Gdk::ModifierType::ALT_MASK)
      {
        // and the second radio button, when we press Alt + 2
        m_second.set_active();
        return true;
      }
      else if (keyval == GDK_KEY_Escape)
      {
        // Close the window, when the 'Esc' key is pressed
        close();
        return true;
      }

      // The event has not been handled
      return false;
    }

    ExampleWindow::~ExampleWindow()
    {
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

## Tempo limite, E/S e funções ociosas

### Tempos limites

You may be wondering how to make gtkmm do useful work while it's idling along. Happily, you have several options. Using the following methods you can create a timeout method that will be called every few milliseconds.

    sigc::connection Glib::SignalTimeout::connect(const sigc::slot<bool()>& slot,
                                          unsigned int interval, int priority = Glib::PRIORITY_DEFAULT);

The first argument is a slot you wish to have called when the timeout occurs. The second argument is the number of milliseconds between calls to that method. You receive a sigc::connection object that can be used to deactivate the connection using its disconnect() method:

    my_connection.disconnect();

Another way of destroying the connection is your signal handler. It has to be of the type sigc::slot<bool()>. As you see from the definition your signal handler has to return a value of the type `bool`. A definition of a sample method might look like this:

    bool MyCallback() { std::cout << "Hello World!\n" << std::endl; return true; }

You can stop the timeout method by returning `false` from your signal handler. Therefore, if you want your method to be called repeatedly, it should return `true`.

Here's an example of this technique:

Source Code

File: `timerexample.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_TIMEREXAMPLE_H
    #define GTKMM_EXAMPLE_TIMEREXAMPLE_H

    #include <gtkmm.h>
    #include <iostream>
    #include <map>

    class TimerExample : public Gtk::Window
    {
    public:
      TimerExample();

    protected:
      // signal handlers
      void on_button_add_timer();
      void on_button_delete_timer();
      void on_button_quit();

      // This is the callback function the timeout will call
      bool on_timeout(int timer_number);

      // Member data:

      Gtk::Box m_Box;
      Gtk::Button m_ButtonAddTimer, m_ButtonDeleteTimer, m_ButtonQuit;

      // Keep track of the timers being added:
      int m_timer_number;

      // These two constants are initialized in the constructor's member initializer:
      const int count_value;
      const int timeout_value;

      // STL map for storing our connections
      std::map<int, sigc::connection> m_timers;

      // STL map for storing our timer values.
      // Each timer counts back from COUNT_VALUE to 0 and is removed when it reaches 0
      std::map<int, int> m_counters;
    };

    #endif // GTKMM_EXAMPLE_TIMEREXAMPLE_H

File: `main.cc` (For use with gtkmm 4)

    #include "timerexample.h"
    #include <gtkmm/application.h>

    int main (int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      return app->make_window_and_run<TimerExample>(argc, argv);
    }

File: `timerexample.cc` (For use with gtkmm 4)

    #include "timerexample.h"

    TimerExample::TimerExample() :
      m_Box(Gtk::Orientation::HORIZONTAL, 10),
      m_ButtonAddTimer("_Add", true),
      m_ButtonDeleteTimer("_Remove", true),
      m_ButtonQuit("_Quit", true),
      m_timer_number(0), // start numbering the timers at 0
      count_value(5), // each timer will count down 5 times before disconnecting
      timeout_value(1500) // 1500 ms = 1.5 seconds
    {
      m_Box.set_margin(10);
      set_child(m_Box);
      m_Box.append(m_ButtonAddTimer);
      m_Box.append(m_ButtonDeleteTimer);
      m_Box.append(m_ButtonQuit);
      m_ButtonAddTimer.set_expand();
      m_ButtonDeleteTimer.set_expand();
      m_ButtonQuit.set_expand();

      // Connect the three buttons:
      m_ButtonQuit.signal_clicked().connect(sigc::mem_fun(*this,
                  &TimerExample::on_button_quit));
      m_ButtonAddTimer.signal_clicked().connect(sigc::mem_fun(*this,
                  &TimerExample::on_button_add_timer));
      m_ButtonDeleteTimer.signal_clicked().connect(sigc::mem_fun(*this,
                  &TimerExample::on_button_delete_timer));
    }

    void TimerExample::on_button_quit()
    {
      close();
    }

    void TimerExample::on_button_add_timer()
    {
      // Creation of a new object prevents long lines and shows us a little
      // how slots work.  We have 0 parameters and bool as a return value
      // after calling sigc::bind.
      sigc::slot<bool()> my_slot = sigc::bind(sigc::mem_fun(*this,
                  &TimerExample::on_timeout), m_timer_number);

      // This is where we connect the slot to the Glib::signal_timeout()
      auto conn = Glib::signal_timeout().connect(my_slot,
              timeout_value);

      // Remember the connection:
      m_timers[m_timer_number] = conn;

      // Initialize timer count:
      m_counters[m_timer_number] = count_value + 1;

      // Print some info to the console for the user:
      std::cout << "added timeout " << m_timer_number++ << std::endl;
    }

    void TimerExample::on_button_delete_timer()
    {
      // any timers?
      if(m_timers.empty())
      {
        // no timers left
        std::cout << "Sorry, there are no timers left." << std::endl;
      }
      else
      {
        // get the number of the first timer
        int timer_number = m_timers.begin()->first;

        // Give some info to the user:
        std::cout << "manually disconnecting timer " << timer_number
            << std::endl;

        // Remove the entry in the counter values
        m_counters.erase(timer_number);

        // Diconnect the signal handler:
        m_timers[timer_number].disconnect();

        // Forget the connection:
        m_timers.erase(timer_number);
      }
    }

    bool TimerExample::on_timeout(int timer_number)
    {
      // Print the timer:
      std::cout << "This is timer " << timer_number;

      // decrement and check counter value
      if (--m_counters[timer_number] == 0)
      {
        std::cout << " being disconnected" <<  std::endl;

        // delete the counter entry in the STL MAP
        m_counters.erase(timer_number);

        // delete the connection entry in the STL MAP
        m_timers.erase(timer_number);

        // Note that we do not have to explicitly call disconnect() on the
        // connection since Gtk::Main does this for us when we return false.
        return false;
      }

      // Print the timer value
      std::cout << " - " << m_counters[timer_number] << "/"
          << count_value << std::endl;

     // Keep going (do not disconnect yet):
      return true;
    }

### Monitorando E/S

A nifty feature of Glib (one of the libraries underlying gtkmm) is the ability to have it check for data on a file descriptor for you. This is especially useful for networking applications. The following method is used to do this:

    sigc::connection Glib::SignalIO::connect(const sigc::slot<bool(Glib::IOCondition)>& slot,
                                     Glib::PollFD::fd_t fd, Glib::IOCondition condition,
                                     int priority = Glib::PRIORITY_DEFAULT);

The first argument is a slot you wish to have called when the specified event (see argument 3) occurs on the file descriptor you specify using argument two. Argument three may be one or more (using `|`) of:

- Glib::IOCondition::IO_IN - Call your method when there is data ready for reading on your file descriptor.

- Glib::IOCondition::IO_OUT - Call your method when the file descriptor is ready for writing.

- Glib::IOCondition::IO_PRI - Call your method when the file descriptor has urgent data to be read.

- Glib::IOCondition::IO_ERR - Call your method when an error has occurred on the file descriptor.

- Glib::IOCondition::IO_HUP - Call your method when hung up (the connection has been broken usually for pipes and sockets).

The return value is a sigc::connection that may be used to stop monitoring this file descriptor using its disconnect() method. The slot signal handler should be declared as follows:

    bool input_callback(Glib::IOCondition condition);

where condition is as specified above. As usual the slot is created with `sigc::mem_fun()` (for a member method of an object), or `sigc::ptr_fun()` (for a function). A lambda expression can be used, if you don't need the automatic disconnection that `sigc::mem_fun()` provides when the object goes out of scope.

A little example follows. To use the example just execute it from a terminal; it doesn't create a window. It will create a pipe named `testfifo` in the current directory. Then start another shell and execute `echo "Hello" > testfifo`. The example will print each line you enter until you execute `echo "Q" > testfifo`.

Source Code

File: `main.cc` (For use with gtkmm 4)

    #include <gtkmm/application.h>
    #include <glibmm/main.h>
    #include <glibmm/iochannel.h>
    #include <fcntl.h>
    #include <iostream>

    #include <unistd.h> //The SUN Forte compiler puts F_OK here.

    //The SUN Forte compiler needs these for mkfifo:
    #include <sys/types.h>
    #include <sys/stat.h>

    Glib::RefPtr<Gtk::Application> app;

    int read_fd;
    Glib::RefPtr<Glib::IOChannel> iochannel;

    /*
      send to the fifo with:
      echo "Hello" > testfifo

      quit the program with:
      echo "Q" > testfifo
    */

    // this will be our signal handler for read operations
    // it will print out the message sent to the fifo
    // and quit the program if the message was 'Q'.
    bool MyCallback(Glib::IOCondition io_condition)
    {
      if ((io_condition & Glib::IOCondition::IO_IN) != Glib::IOCondition::IO_IN)
      {
        std::cerr << "Invalid fifo response" << std::endl;
      }
      else
      {
       Glib::ustring buf;

       iochannel->read_line(buf);
       std::cout << buf;
       if (buf == "Q\n")
         app->quit();
      }
      return true;
    }

    int main(int argc, char *argv[])
    {
      app = Gtk::Application::create("org.gtkmm.example");

      if (access("testfifo", F_OK) == -1)
      {
        // fifo doesn't exist - create it
        #ifndef DONT_HAVE_MKFIFO
        if (mkfifo("testfifo", 0666) != 0)
        {
          std::cerr << "error creating fifo" << std::endl;
          return -1;
        }
        #else
          std::cerr << "error creating fifo: This platform does not have mkfifo()"
              << std::endl;
        #endif //DONT_HAVE_MKFIFO
      }

      // Although we will only read from the fifo, we open it in read/write mode.
      // Due to a peculiarity with the poll() system call, used deep down in glib,
      // this small program will use all available CPU time, if the fifo is opened
      // as O_RDONLY. See a discussion on the gtkmm-list, e.g.
      // https://mail.gnome.org/archives/gtkmm-list/2015-September/msg00034.html
      // and the link from there to stackoverflow.
      read_fd = open("testfifo", O_RDWR);
      if (read_fd == -1)
      {
        std::cerr << "error opening fifo" << std::endl;
        return -1;
      }

      // connect the signal handler
      Glib::signal_io().connect(
        [](Glib::IOCondition io_condition){ return MyCallback(io_condition); },
        read_fd, Glib::IOCondition::IO_IN);

      // Creates a iochannel from the file descriptor
      iochannel = Glib::IOChannel::create_from_fd(read_fd);

      // and last but not least - run the application main loop
      app->hold(); // keep the application running without a window
      app->run(argc, argv);

      // now remove the temporary fifo
      if(unlink("testfifo"))
        std::cerr << "error removing fifo" << std::endl;

      return 0;
    }

### Funções ociosas

If you want to specify a method that gets called when nothing else is happening, use the following:

    sigc::connection  Glib::SignalIdle::connect(const sigc::slot<bool()>& slot,
                                        int priority = Glib::PRIORITY_DEFAULT_IDLE);

This causes gtkmm to call the specified method whenever nothing else is happening. You can add a priority (lower numbers are higher priorities). There are two ways to remove the signal handler: calling disconnect() on the sigc::connection object, or returning `false` in the signal handler, which should be declared as follows:

    bool idleFunc();

Since this is very similar to the methods above this explanation should be sufficient to understand what's going on. However, here's a little example:

Source Code

File: `idleexample.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_IDLEEXAMPLE_H
    #define GTKMM_EXAMPLE_IDLEEXAMPLE_H

    #include <gtkmm.h>
    #include <iostream>

    class IdleExample : public Gtk::Window
    {
    public:
      IdleExample();

    protected:
      // Signal Handlers:
      bool on_timer();
      bool on_idle();
      void on_button_clicked();

      // Member data:
      Gtk::Box m_Box;
      Gtk::Button m_ButtonQuit;
      Gtk::ProgressBar m_ProgressBar_c;
      Gtk::ProgressBar m_ProgressBar_d;
    };

    #endif // GTKMM_EXAMPLE_IDLEEXAMPLE_H

File: `idleexample.cc` (For use with gtkmm 4)

    #include "idleexample.h"

    IdleExample::IdleExample() :
      m_Box(Gtk::Orientation::VERTICAL, 5),
      m_ButtonQuit("_Quit", true)
    {
      m_Box.set_margin(5);

      // Put buttons into container

      // Adding a few widgets:
      set_child(m_Box);
      m_Box.append(*Gtk::make_managed<Gtk::Label>("Formatting Windows drive C:"));
      m_Box.append(*Gtk::make_managed<Gtk::Label>("100 MB"));
      m_Box.append(m_ProgressBar_c);
      m_ProgressBar_c.set_expand();

      m_Box.append(*Gtk::make_managed<Gtk::Label>(""));

      m_Box.append(*Gtk::make_managed<Gtk::Label>("Formatting Windows drive D:"));
      m_Box.append(*Gtk::make_managed<Gtk::Label>("5000 MB"));
      m_Box.append(m_ProgressBar_d);
      m_ProgressBar_d.set_expand();

      auto hbox = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::HORIZONTAL,10);
      m_Box.append(*hbox);
      hbox->append(m_ButtonQuit);
      m_ButtonQuit.set_expand();
      m_ButtonQuit.set_halign(Gtk::Align::END);
      m_ButtonQuit.set_valign(Gtk::Align::END);

      // Connect the signal handlers:
      m_ButtonQuit.signal_clicked().connect( sigc::mem_fun(*this,
                  &IdleExample::on_button_clicked) );

      // formatting drive c in timeout signal handler - called once every 50ms
      Glib::signal_timeout().connect( sigc::mem_fun(*this, &IdleExample::on_timer),
              50 );

      // formatting drive d in idle signal handler - called as quickly as possible
      Glib::signal_idle().connect( sigc::mem_fun(*this, &IdleExample::on_idle) );
    }

    void IdleExample::on_button_clicked()
    {
      close();
    }

    // this timer callback function is executed once every 50ms (set in connection
    // above).  Use timeouts when speed is not critical. (ie periodically updating
    // something).
    bool IdleExample::on_timer()
    {
      double value = m_ProgressBar_c.get_fraction();

      // Update progressbar 1/500th each time:
      m_ProgressBar_c.set_fraction(value + 0.002);

      return value < 0.99;  // return false when done
    }

    // This idle callback function is executed as often as possible, hence it is
    // ideal for processing intensive tasks.
    bool IdleExample::on_idle()
    {
      double value = m_ProgressBar_d.get_fraction();

      // Update progressbar 1/5000th each time:
      m_ProgressBar_d.set_fraction(value + 0.0002);

      return value < 0.99;  // return false when done
    }

File: `main.cc` (For use with gtkmm 4)

    #include "idleexample.h"
    #include <gtkmm/application.h>

    int main (int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      return app->make_window_and_run<IdleExample>(argc, argv);
    }

This example points out the difference of idle and timeout methods a little. If you need methods that are called periodically, and speed is not very important, then you want timeout methods. If you want methods that are called as often as possible (like calculating a fractal in background), then use idle methods.

Try executing the example and increasing the system load. The upper progress bar will increase steadily; the lower one will slow down.

## Gerenciamento de memória

### Widgets

#### Gerenciamento de memória normal em C++

gtkmm allows the programmer to control the lifetime (that is, the construction and destruction) of any widget in the same manner as any other C++ object. This flexibility allows you to use `new` and `delete` to create and destroy objects dynamically or to use regular class members (that are destroyed automatically when the class is destroyed) or to use local instances (that are destroyed when the instance goes out of scope). This flexibility is not present in some C++ GUI toolkits, which restrict the programmer to only a subset of C++'s memory management features.

An important difference in gtkmm-4.0 vs. older versions is that a C++ widgetʼs destruction no longer causes the widget to be destroyed if itʼs within a parent; in that case the C GtkWidget stays alive. If you had relied on that behavior in an older version, in gtkmm-4.0 you must now remove the widget from its parent first. See Changes in gtkmm-4.0.

Here are some examples of normal C++ memory management:

##### Class Scope widgets

If a programmer does not need dynamic memory allocation, automatic widgets in class scope may be used. One advantage of automatic widgets in class scope is that memory management is grouped in one place. The programmer does not risk memory leaks from failing to `delete` a widget.

The primary disadvantage of using class scope widgets is revealing the class implementation rather than the class interface in the class header.

    #include <gtkmm/button.h>
    #include <gtkmm/window.h>
    class Foo : public Gtk::Window
    {
    private:
      Gtk::Button theButton;
      // will be destroyed when the Foo object is destroyed
    };

##### Function scope widgets

If a programmer does not need a class scope widget, a function scope widget may also be used. The advantages to function scope over class scope are the increased data hiding and reduced dependencies.

    {
      Gtk::Button aButton;
      aButton.set_visible(true);
      ...
      app->run();
    }

However, this technique is rarely useful. Most widgets can't safely be created before the application has been registered or activated. They can't safely be deleted after Gtk::Application::run() or Gtk::Application::make_window_and_run() returns.

##### Dynamic allocation with new and delete

Usually, the programmer will prefer to allow containers to automatically destroy their children by creating them using `Gtk::make_managed()` (see below). This is not strictly required, as the `new` and `delete` operators may also be used, but modern C++ style discourages those in favor of safer models of memory management, so it is better to create widgets using `Gtk::make_managed()` and let their parent destroy them, than to manually perform dynamic allocation.

    auto pButton = new Gtk::Button("Test");
    // do something useful with pButton
    delete pButton;

Here, the programmer deletes `pButton` to prevent a memory leak.

#### Widgets gerenciados

Alternatively, you can let a widget's container control when the widget is destroyed. In most cases, you want a widget to last only as long as the container it is in. To delegate the management of a widget's lifetime to its container, create it with `Gtk::make_managed()` and then pack it into its container with Gtk::Box::append() or a similar method. Now the widget will be destroyed whenever its container is destroyed.

##### Dynamic allocation with make_managed() and append()

gtkmm provides ways including the `make_managed()` function and Gtk::Box::append() method to simplify creation and destruction of widgets whose lifetime can be managed by a parent.

Every widget except a top-level window must be added to a parent container in order to be displayed. The `manage()` function marks a widget so that when that widget is added to a parent container, said container becomes responsible for deleting the widget, meaning the user no longer needs to do so. The original way to create widgets whose lifetime is managed by their parent in this way was to call `manage()`, passing in the result of a `new` expression that created a dynamically allocated widget.

However, usually, when you create such a widget, you will already know that its parent container should be responsible for destroying it. In addition, modern C++ style discourages use of the `new` operator, which was required when passing a newly created widget to `manage()`. Therefore, gtkmm has added `make_managed()`, which combines creation and marking with `manage()` into a single step. This avoids you having to write `new`, which is discouraged in modern C++ style, and more clearly expresses intent to create a managed widget.

    MyContainer::MyContainer()
    {
      auto pButton = Gtk::make_managed<Gtk::Button>("Test");
      append(*pButton); //add *pButton to MyContainer
    }

Now, when objects of type MyContainer are destroyed, the button will also be deleted. It is no longer necessary to delete `pButton` to free the button's memory; its deletion has been delegated to the MyContainer object.

If you never added the widget to any parent container, it's your responsibility to delete it. If you add it to a container widget, and later remove it (for instance with Gtk::Box::remove()), it's deleted by the container.

Of course, a top-level container will not be added to another container. The programmer is responsible for destroying the top-level container using one of the traditional C++ techniques. Or you can let Gtk::Application::make_window_and_run() create a top-level window and delete it when it's closed.

### Recursos compartilhados

Some objects, such as Gdk::Pixbufs and Pango::Fonts, are obtained from a shared store. Therefore you cannot instantiate your own instances. These classes typically inherit from Glib::Object. Rather than requiring you to reference and unreference these objects, gtkmm uses the Glib::RefPtr<> smartpointer. Cairomm has its own smartpointer, Cairo::RefPtr<>.

Objects such as Gdk::Pixbuf can only be instantiated with a create() function. For instance,

    auto pixbuf = Gdk::Pixbuf::create_from_file(filename);

You have no way of getting a bare Gdk::Pixbuf. In the example, `pixbuf` is a smart pointer, so you can do this, much like a normal pointer:

    auto width = 0;
    if(pixbuf)
    {
      width = pixbuf->get_width();
    }

When `pixbuf` goes out of scope an unref() will happen in the background and you don't need to worry about it anymore. There's no `new` so there's no `delete`.

If you copy a RefPtr, for instance

    auto pixbuf2 = pixbuf;

or if you pass it as a method argument or a return type, then RefPtr will do any necessary referencing to ensure that the instance will not be destroyed until the last RefPtr has gone out of scope.

Veja o apêndice para obter informações detalhadas sobre RefPtr.

If you wish to learn more about smartpointers, you might look in these books:

- Bjarne Stroustrup, "The C++ Programming Language" Fourth Edition - section 34.3

- Nicolai M. Josuttis, "The C++ Standard Library" - section 4.2

## Gtk::Builder

Although you can use C++ code to instantiate and arrange widgets, this can soon become tedious and repetitive. And it requires a recompilation to show changes. The Cambalache application allows you to layout widgets on screen and then save an XML description of the arrangement. Your application can then use the Gtk::Builder API to load that XML file at runtime and obtain a pointer to specifically named widget instances.

This has the following advantages:

1. Less C++ code is required.

2. UI changes can be seen more quickly, so UIs are able to improve.

3. Designers without programming skills can create and edit UIs.

You still need C++ code to deal with User Interface changes triggered by user actions, but using Gtk::Builder for the widget layout allows you to focus on implementing that functionality.

Cambalache replaces the Glade application. Glade can generate XML files to be used with gtk3/gtkmm3, but it does not support gtk4/gtkmm4.

### Loading the .ui file

Gtk::Builder must be used via a Glib::RefPtr. Like all such classes, you need to use a create() method to instantiate it. For instance,

    auto builder = Gtk::Builder::create_from_file("basic.ui");

This will instantiate the windows defined in the `.ui` file.

To instantiate just one window, or just one of the child widgets, you can specify the name of a widget as the second parameter. For instance,

    auto builder = Gtk::Builder::create_from_file("basic.ui", "treeview_products");

### Acessando widgets

To access a widget, for instance to show a dialog, use the get_widget() method, providing the widget's name. This name should be specified in the Cambalache window. If the widget could not be found, or is of the wrong type, then the pointer will be set to `nullptr`.

The dialogs in this chapter are derived from Gtk::Window because Gtk::Dialog is deprecated since gtkmm 4.10.

    auto pDialog = builder->get_widget<Gtk::Window>("DialogBasic");

Gtk::Builder checks for a null pointer, and checks that the widget is of the expected type, and will show warnings on the command line about these.

Remember that you are not instantiating a widget with get_widget(), you are just obtaining a pointer to one that already exists. You will always receive a pointer to the same instance when you call get_widget() on the same Gtk::Builder, with the same widget name. The widgets are instantiated during Gtk::Builder::create_from_file().

get_widget() returns child widgets that are `manage()`ed (see the Memory Management chapter), so they will be deleted when their parent container is deleted. Windows (such as Dialogs) cannot be managed because they have no parent container, so you must delete them at some point. The documentation of Gtk::Builder has more to say about the memory management of different kinds of objects.

Reference

#### Exemplo

This simple example shows how to load a `.ui` file at runtime and access the widgets with Gtk::Builder.

Source Code

File: `main.cc` (For use with gtkmm 4)

    #include <gtkmm.h>
    #include <iostream>

    namespace
    {
    Gtk::Window* pDialog = nullptr;
    Glib::RefPtr<Gtk::Application> app;

    void on_button_clicked()
    {
      // When the application's only window is removed with
      // unset_application(), Gtk::Application::run() will end.
      if (pDialog)
        pDialog->unset_application();
    }

    void on_app_activate()
    {
      // Load the GtkBuilder file and instantiate its widgets:
      auto refBuilder = Gtk::Builder::create();
      try
      {
        refBuilder->add_from_file("basic.ui");
      }
      catch(const Glib::FileError& ex)
      {
        std::cerr << "FileError: " << ex.what() << std::endl;
        return;
      }
      catch(const Glib::MarkupError& ex)
      {
        std::cerr << "MarkupError: " << ex.what() << std::endl;
        return;
      }
      catch(const Gtk::BuilderError& ex)
      {
        std::cerr << "BuilderError: " << ex.what() << std::endl;
        return;
      }

      // Get the GtkBuilder-instantiated dialog:
      pDialog = refBuilder->get_widget<Gtk::Window>("DialogBasic");
      if (!pDialog)
      {
        std::cerr << "Could not get the dialog" << std::endl;
        return;
      }

      // Get the GtkBuilder-instantiated button, and connect a signal handler:
      auto pButton = refBuilder->get_widget<Gtk::Button>("quit_button");
      if (pButton)
        pButton->signal_clicked().connect([] () { on_button_clicked(); });

      // It's not possible to delete widgets after app->run() has returned.
      // Delete the dialog with its child widgets before app->run() returns.
      app->signal_window_removed().connect([](Gtk::Window* window) { delete window; });

      app->add_window(*pDialog);
      pDialog->set_visible(true);
    }
    } // anonymous namespace

    int main(int argc, char** argv)
    {
      app = Gtk::Application::create("org.gtkmm.example");

      // Instantiate a dialog when the application has been activated.
      // This can only be done after the application has been registered.
      // It's possible to call app->register_application() explicitly, but
      // usually it's easier to let app->run() do it for you.
      app->signal_activate().connect([] () { on_app_activate(); });

      return app->run(argc, argv);
    }

### Usando widgets derivados

You can use Cambalache and Gtk::Builder to layout your own custom widgets derived from gtkmm widget classes. This keeps your code organized and encapsulated, separating declarative presentation from business logic, avoiding having most of your source just be setting properties and packing in containers.

Use Gtk::Builder::get_widget_derived() like so:

    auto pDialog = Gtk::Builder::get_widget_derived<DerivedDialog>(builder, "DialogDerived");

Your derived class must have a constructor that takes a pointer to the underlying C type, and the Gtk::Builder instance. All relevant classes of gtkmm typedef their underlying C type as BaseObjectType (Gtk::Window typedefs BaseObjectType as GtkWindow, for instance).

You must call the base class's constructor in the initialization list, providing the C pointer. For instance,

    DerivedDialog::DerivedDialog(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& builder)
    : Gtk::Window(cobject)
    {
    }

You could then encapsulate the manipulation of the child widgets in the constructor of the derived class, maybe using get_widget() or get_widget_derived() again. For instance,

    DerivedDialog::DerivedDialog(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& builder)
    : Gtk::Window(cobject),
      m_builder(builder),
      // Get the GtkBuilder-instantiated Button, and connect a signal handler:
      m_pButton(m_builder->get_widget<Gtk::Button>("quit_button"))
    {
      if (m_pButton)
      {
        m_pButton->signal_clicked().connect( sigc::mem_fun(*this, &DerivedDialog::on_button_quit) );
      }
    }

It's possible to pass additional arguments from get_widget_derived() to the constructor of the derived widget. For instance, this call to get_widget_derived()

    auto pDialog = Gtk::Builder::get_widget_derived<DerivedDialog>(builder, "DialogDerived", true);

can invoke this constructor

    DerivedDialog::DerivedDialog(BaseObjectType* cobject,
      const Glib::RefPtr<Gtk::Builder>& builder, bool warning)
    : Gtk::Window(cobject),
      m_builder(builder),
      m_pButton(m_builder->get_widget<Gtk::Button>("quit_button"))
    {
      // ....
    }

#### Gtk::Builder and Glib::Property

If your derived widget uses Glib::Property, it becomes slightly more complicated. A derived widget that contains Glib::Property members must be registered with its own name in the GType system. It must be registered before any of the create_from_*() or add_from_*() methods are called, meaning that you may have to create an instance of your derived widget just to have its class registered. Your derived widget must have a constructor that has the parameters required by get_widget_derived() and calls the Glib::ObjectBase constructor to register the GType.

    DerivedButton::DerivedButton(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& builder)
    : Glib::ObjectBase("MyButton"), // The GType name will be gtkmm__CustomObject_MyButton.
      Gtk::Button(cobject),
      prop_ustring(*this, "button-ustring"),
      prop_int(*this, "button-int", 10)
    {
      // ....
    }

It is possible also to specify properties of derived widgets, declared in C++ using gtkmm, within `.ui` files and load/set these using Gtk::Builder. See the documentation of Gtk::Builder for more details on how to achieve this. Cambalache won’t recognize such properties as-is, but you should be able to add a few lines of hand-coded XML to the XML code generated by Cambalache.

#### Exemplo

This example shows how to load a `.ui` file at runtime and access the widgets via derived classes.

Source Code

File: `derivedbutton.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_DERIVED_BUTTON_H
    #define GTKMM_EXAMPLE_DERIVED_BUTTON_H

    #include <gtkmm.h>

    class DerivedButton : public Gtk::Button
    {
    public:
      DerivedButton();
      DerivedButton(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& refBuilder);
      virtual ~DerivedButton();

      // Provide proxies for the properties. The proxy allows you to connect to
      // the 'changed' signal, etc.
      Glib::PropertyProxy<Glib::ustring> property_ustring() { return prop_ustring.get_proxy(); }
      Glib::PropertyProxy<int> property_int() { return prop_int.get_proxy(); }

    private:
      Glib::Property<Glib::ustring> prop_ustring;
      Glib::Property<int> prop_int;
    };

    #endif //GTKMM_EXAMPLE_DERIVED_BUTTON_H

File: `deriveddialog.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_DERIVED_DIALOG_H
    #define GTKMM_EXAMPLE_DERIVED_DIALOG_H

    #include <gtkmm.h>
    #include "derivedbutton.h"

    class DerivedDialog : public Gtk::Window
    {
    public:
      DerivedDialog(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& refBuilder);
      DerivedDialog(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& refBuilder,
        bool is_glad);
      ~DerivedDialog() override;

    protected:
      //Signal handlers:
      void on_button_quit();

      Glib::RefPtr<Gtk::Builder> m_refBuilder;
      DerivedButton* m_pButton;
    };

    #endif //GTKMM_EXAMPLE_DERIVED_DIALOG_H

File: `derivedbutton.cc` (For use with gtkmm 4)

    #include "derivedbutton.h"
    #include <iostream>

    // For creating a dummy object in main.cc.
    DerivedButton::DerivedButton()
    : Glib::ObjectBase("MyButton"),
      prop_ustring(*this, "button-ustring"),
      prop_int(*this, "button-int", 10)
    {
    }

    DerivedButton::DerivedButton(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& /* refBuilder */)
    : // To register custom properties, you must register a custom GType.  If
      // you don't know what that means, don't worry, just remember to add
      // this Glib::ObjectBase constructor call to your class' constructor.
      // The GType name will be gtkmm__CustomObject_MyButton.
      Glib::ObjectBase("MyButton"),
      Gtk::Button(cobject),
      // register the properties with the object and give them names
      prop_ustring(*this, "button-ustring"),
      // this one has a default value
      prop_int(*this, "button-int", 10)
    {
      // Register some handlers that will be called when the values of the
      // specified parameters are changed.
      property_ustring().signal_changed().connect(
        [](){ std::cout << "- ustring property changed!" << std::endl; }
      );
      property_int().signal_changed().connect(
        [](){ std::cout << "- int property changed!" << std::endl; }
      );
    }

    DerivedButton::~DerivedButton()
    {
    }

File: `deriveddialog.cc` (For use with gtkmm 4)

    #include "deriveddialog.h"
    #include <iostream>

    DerivedDialog::DerivedDialog(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& refBuilder)
    : Gtk::Window(cobject),
      m_refBuilder(refBuilder),
      m_pButton(nullptr)
    {
      // Get the GtkBuilder-instantiated Button, and connect a signal handler:
      m_pButton = Gtk::Builder::get_widget_derived<DerivedButton>(m_refBuilder, "quit_button");
      if (m_pButton)
      {
        m_pButton->signal_clicked().connect( sigc::mem_fun(*this, &DerivedDialog::on_button_quit) );
        std::cout << "ustring, int: " << m_pButton->property_ustring()
                  << ", " << m_pButton->property_int() << std::endl;
        m_pButton->property_int() = 99;
        std::cout << "ustring, int: " << m_pButton->property_ustring()
                  << ", " << m_pButton->property_int() << std::endl;
      }
    }

    // The first two parameters are mandatory in a constructor that will be called
    // from Gtk::Builder::get_widget_derived().
    // Additional parameters, if any, correspond to additional arguments in the call
    // to Gtk::Builder::get_widget_derived().
    DerivedDialog::DerivedDialog(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& refBuilder,
      bool is_glad)
    : DerivedDialog(cobject, refBuilder) // Delegate to the other constructor
    {
      // Show an icon.
      auto content_area = refBuilder->get_widget<Gtk::Box>("dialog-content_area");
      if (!content_area)
      {
        std::cerr << "Could not get the content area" << std::endl;
        return;
      }
      auto pImage = Gtk::make_managed<Gtk::Image>();
      pImage->set_from_icon_name(is_glad ? "face-smile" : "face-sad");
      pImage->set_icon_size(Gtk::IconSize::LARGE);
      pImage->set_expand();
      content_area->append(*pImage);
    }

    DerivedDialog::~DerivedDialog()
    {
    }

    void DerivedDialog::on_button_quit()
    {
      // When the application's only window is removed with
      // unset_application(), Gtk::Application::run() will end.
      unset_application();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "deriveddialog.h"
    #include <iostream>
    #include <cstring>

    namespace
    {
    bool show_icon = false;
    bool is_glad = true;

    DerivedDialog* pDialog = nullptr;
    Glib::RefPtr<Gtk::Application> app;

    void on_app_activate()
    {
      // Create a dummy instance before the call to refBuilder->add_from_file().
      // This creation registers DerivedButton's class in the GType system.
      // This is necessary because DerivedButton contains user-defined properties
      // (Glib::Property) and is created by Gtk::Builder.
      static_cast<void>(DerivedButton());

      // Load the GtkBuilder file and instantiate its widgets:
      auto refBuilder = Gtk::Builder::create();
      try
      {
        refBuilder->add_from_file("derived.ui");
      }
      catch(const Glib::FileError& ex)
      {
        std::cerr << "FileError: " << ex.what() << std::endl;
        return;
      }
      catch(const Glib::MarkupError& ex)
      {
        std::cerr << "MarkupError: " << ex.what() << std::endl;
        return;
      }
      catch(const Gtk::BuilderError& ex)
      {
        std::cerr << "BuilderError: " << ex.what() << std::endl;
        return;
      }

      // Get the GtkBuilder-instantiated dialog:
      if (show_icon)
        pDialog = Gtk::Builder::get_widget_derived<DerivedDialog>(refBuilder, "DialogDerived", is_glad);
      else
        pDialog = Gtk::Builder::get_widget_derived<DerivedDialog>(refBuilder, "DialogDerived");

      if (!pDialog)
      {
        std::cerr << "Could not get the dialog" << std::endl;
        return;
      }

      // It's not possible to delete widgets after app->run() has returned.
      // Delete the dialog with its child widgets before app->run() returns.
      app->signal_window_removed().connect([](Gtk::Window* window) { delete window; });

      app->add_window(*pDialog);
      pDialog->set_visible(true);
    }
    } // anonymous namespace

    int main(int argc, char** argv)
    {
      int argc1 = argc;
      if (argc > 1)
      {
        if (std::strcmp(argv[1], "--glad") == 0)
        {
          show_icon = true;
          is_glad = true;
          argc1 = 1; // Don't give the command line arguments to Gtk::Application.
        }
        else if (std::strcmp(argv[1], "--sad") == 0)
        {
          show_icon = true;
          is_glad = false;
          argc1 = 1; // Don't give the command line arguments to Gtk::Application.
        }
      }

      app = Gtk::Application::create("org.gtkmm.example");

      // Instantiate a dialog when the application has been activated.
      // This can only be done after the application has been registered.
      // It's possible to call app->register_application() explicitly, but
      // usually it's easier to let app->run() do it for you.
      app->signal_activate().connect([] () { on_app_activate(); });

      return app->run(argc1, argv);
    }

## Internacionalização e localização

gtkmm applications can easily support multiple languages, including non-European languages such as Chinese and right-to-left languages such as Arabic. An appropriately-written and translated gtkmm application will use the appropriate language at runtime based on the user's environment.

You might not anticipate the need to support additional languages, but you can never rule it out. And it's easier to develop the application properly in the first place rather than retrofitting later.

The process of writing source code that allows for translation is called `internationalization`, often abbreviated to `i18n`. The `Localization` process, sometimes abbreviated as `l10n`, provides translated text for other languages, based on that source code.

The main activity in the internationalization process is finding strings seen by users and marking them for translation. You do not need to do it all at once - if you set up the necessary project infrastructure correctly then your application will work normally regardless of how many strings you've covered.

String literals should be typed in the source code in English, but surrounded by a macro. The gettext (or intltool) utility can then extract the marked strings for translation, and substitute the translated text at runtime.

### Preparando seu projeto

In the instructions below we will assume that you will not be using gettext directly, but intltool, which was written specifically for `GNOME`. intltool uses `gettext()`, which extracts strings from source code, but intltool can also combine strings from other files, for example from desktop menu details, and GUI resource files such as `.ui` files, into standard gettext `.pot/.po` files.

We also assume that you are using autotools (automake and autoconf) to build your project (although autotools is not recommended for new applications), and that you are using `./autogen.sh` from gnome-common or a similar `autogen.sh` file, which, among other things, takes care of some intltool initialization.

If you are using meson (recommended), see the Localisation chapter in Meson's manual. You can then skip this section.

An alternative to gnome-common's `autogen.sh` may look like this:

    #! /bin/sh -e
    test -n "$srcdir" || srcdir=`dirname "$0"`
    test -n "$srcdir" || srcdir=.

    autoreconf --force --install --verbose --warnings=all "$srcdir"
    echo "Running intltoolize --copy --force --automake"
    intltoolize --copy --force --automake
    test -n "$NOCONFIGURE" || "$srcdir/configure" "$@"

Create a sub-directory named `po` in your project's root directory. This directory will eventually contain all of your translations. Within it, create a file named `LINGUAS` and a file named `POTFILES.in`.

`LINGUAS` contains an alphabetically sorted list of codes identifying the languages for which your program is translated (comment lines starting with a `#` are ignored). Each language code listed in the `LINGUAS` file must have a corresponding `.po` file. So, if your program has German and Japanese translations, your `LINGUAS` file would look like this:

    # keep this file sorted alphabetically, one language code per line
    de
    ja

(In addition, you'd have the files `de.po` and `ja.po` in your `po` directory which contain the German and Japanese translations, respectively.)

`POTFILES.in` is a list of paths to all files which contain strings marked up for translation, starting from the project root directory. So for example, if your project sources were located in a subdirectory named `src`, and you had two files that contained strings that should be translated, your `POTFILES.in` file might look like this:

    src/main.cc
    src/other.cc

If you are using gettext directly, you can only mark strings for translation if they are in source code file. However, if you use intltool, you can mark strings for translation in a variety of other file formats, including `.ui` files, xml, .desktop files and several more. So, if you have designed some of the application UI in xml files then also add your `.ui` files to the list in `POTFILES.in`.

Now that there is a place to put your translations, you need to initialize intltool and gettext. Add the following code to your `configure.ac`, substituting 'programname' with the name of your program:

    IT_PROG_INTLTOOL([0.35.0])

    GETTEXT_PACKAGE=programname
    AC_SUBST(GETTEXT_PACKAGE)
    AC_DEFINE_UNQUOTED([GETTEXT_PACKAGE], ["$GETTEXT_PACKAGE"],
                       [The domain to use with gettext])
    AM_GNU_GETTEXT([external])
    AM_GNU_GETTEXT_VERSION([0.17])

    PROGRAMNAME_LOCALEDIR=[${datadir}/locale]
    AC_SUBST(PROGRAMNAME_LOCALEDIR)

This `PROGRAMNAME_LOCALEDIR` variable will be used later in the `Makefile.am` file, to define a macro that will be used when you initialize gettext in your source code.

`AM_GLIB_GNU_GETTEXT` has been an alternative to `AM_GNU_GETTEXT` and `AM_GNU_GETTEXT_VERSION`, but `AM_GLIB_GNU_GETTEXT` is now deprecated, and shall not be used in new code.

In the top-level Makefile.am:

- Add `po` to the `SUBDIRS` variable. Without this, your translations won't get built and installed when you build the program

- Define `INTLTOOL_FILES` as:

      INTLTOOL_FILES = intltool-extract.in \
                       intltool-merge.in \
                       intltool-update.in

- Add `INTLTOOL_FILES` to the `EXTRA_DIST` list of files. This ensures that when you do a `make dist`, these files will be included in the source tarball.

- Update your `DISTCLEANFILES`:

      DISTCLEANFILES = ... intltool-extract \
                       intltool-merge \
                       intltool-update \
                       po/.intltool-merge-cache

- Depending on the types of files that contain translatable strings, add code such as

      desktopdir = $(datadir)/applications
      desktop_in_files = programname.desktop.in
      desktop_DATA = $(desktop_in_files:.desktop.in=.desktop)
      @INTLTOOL_DESKTOP_RULE@

In your `src/Makefile.am`, update your `AM_CPPFLAGS` to add the following preprocessor macro definition:

    AM_CPPFLAGS = ... -DPROGRAMNAME_LOCALEDIR=\"${PROGRAMNAME_LOCALEDIR}\"

This macro will be used when you initialize `gettext` in your source code.

### Marcando strings para tradução

String literals should be typed in the source code in English, but they should be surrounded by a call to the `gettext()` function. These strings will be extracted for translation and the translations may be used at runtime instead of the original English strings.

The GNU gettext package allows you to mark strings in source code, extract those strings for translation, and use the translated strings in your application.

However, Glib defines `gettext()` support macros which are shorter wrappers in an easy-to-use form. To use these macros, include `<glibmm/i18n.h>`, and then, for example, substitute:

    display_message("Getting ready for i18n.");

with:

    display_message(_("Getting ready for i18n."));

For reference, it is possible to generate a file which contains all strings which appear in your code, even if they are not marked for translation, together with file name and line number references. To generate such a file named `my-strings`, execute the following command, within the source code directory:

    xgettext -a -o my-strings --omit-header *.cc *.h

Finally, to let your program use the translation for the current locale, add this code to the beginning of your `main.cc` file, to initialize gettext.

    bindtextdomain(GETTEXT_PACKAGE, PROGRAMNAME_LOCALEDIR);
    bind_textdomain_codeset(GETTEXT_PACKAGE, "UTF-8");
    textdomain(GETTEXT_PACKAGE);

#### Como funciona o gettext

The intltool-update or xgettext script extracts the strings and puts them in a `mypackage.pot` file. The translators of your application create their translations by first copying this `.pot` file to a `localename.po` file. A locale identifies a language and an encoding for that language, including date and numerical formats. Later, when the text in your source code has changed, the msgmerge or intltool-update script is used to update the `localename.po` files from the regenerated `.pot` file.

At install time, the `.po` files are converted to a binary format (with the extension `.mo`) and placed in a system-wide directory for locale files, for example `/usr/share/locale/`.

When the application runs, the gettext library checks the system-wide directory to see if there is a `.mo` file for the user's locale environment (you can set the locale with, for instance, "export LANG=de_DE.UTF-8" from a bash console). Later, when the program reaches a `gettext` call, it looks for a translation of a particular string. If none is found, the original string is used.

#### Testando e adicionando traduções

To convince yourself that you've done well, you may wish to add a translation for a new locale. In order to do that, go to the `po` subdirectory of your project and execute the following command:

    intltool-update --pot --gettext-package programname

That will create a file named `programname.pot`. Now copy that file to `languagecode.po`, such as `de.po` or `hu.po`. Also add that language code to `LINGUAS`. The `.po` file contains a header and a list of English strings, with space for the translated strings to be entered. Make sure you set the encoding of the `.po` file to `UTF-8`.

    "Content-Type: text/plain; charset=UTF-8\n"

It's possible that certain strings will be marked as `fuzzy` in the `.po` file. These translations will not substitute the original string. To make them appear, simply remove the `fuzzy` tag. A `fuzzy` tag appears if a string content changed, but the location is still the same.

#### Recursos

More information about what lies behind the internationalization and localization process is presented and demonstrated in:

- L10N Guidelines for Developers

- Intltool README

- How to use Git for GNOME translators

- gettext manual

### Esperando UTF8

A properly internationalized application will not make assumptions about the number of bytes in a character. That means that you shouldn't use pointer arithmetic to step through the characters in a string, and it means you shouldn't use std::string or standard C functions such as `strlen()` because they make the same assumption.

However, you probably already avoid bare char* arrays and pointer arithmetic by using std::string, so you just need to start using Glib::ustring instead. See the Basics chapter about Glib::ustring.

#### Glib::ustring and std::iostreams

Unfortunately, the integration with the standard iostreams is not completely foolproof. gtkmm converts Glib::ustrings to a locale-specific encoding (which usually is not UTF-8) if you output them to an ostream with `operator<<`. Likewise, retrieving Glib::ustrings from istream with `operator>>` causes a conversion in the opposite direction. But this scheme breaks down if you go through a std::string, e.g. by inputting text from a stream to a std::string and then implicitly converting it to a Glib::ustring. If the string contained non-ASCII characters and the current locale is not UTF-8 encoded, the result is a corrupted Glib::ustring. You can work around this with a manual conversion. For instance, to retrieve the std::string from a ostringstream:

    std::locale::global(std::locale("")); // Set the global locale to the user's preferred locale.
                                          // Usually unnecessary here, because Glib::init()
                                          // or Gtk::Application::create() does it for you.
    std::ostringstream output;
    output << percentage << " % done";
    label->set_text(Glib::locale_to_utf8(output.str()));

### Pitfalls

There are a few common mistakes that you would discover eventually yourself. But this section might help you to avoid them.

#### Mesmas strings, semânticas diferentes

Sometimes two English strings are identical but have different meanings in different contexts, so they would probably not be identical when translated. Since the English strings are used as look-up keys, this causes problems.

In these cases, you should add extra characters to the strings. For instance, use `"jumps[noun]"` and `"jumps[verb]"` instead of just `"jumps"` and strip them again outside the `gettext` call. If you add extra characters you should also add a comment for the translators before the `gettext` call. Such comments will be shown in the `.po` files. For instance:

    // note to translators: don't translate the "[noun]" part - it is
    // just here to distinguish the string from another "jumps" string
    text = strip(gettext("jumps[noun]"), "[noun]");

If you use Glib's support macros, it's easier. Use `C_()` instead of `_()`. For instance:

    GLib::ustring text(C_("noun", "jumps"));

#### Composição de strings

C programmers use `sprintf()` to compose and concatenate strings. C++ favors streams, but unfortunately, this approach makes translation difficult, because each fragment of text is translated separately, without allowing the translators to rearrange them according to the grammar of the language.

For instance, this code would be problematic:

    std::cout << _("Current amount: ") << amount
              << _(" Future: ") << future << std::endl;

    label.set_text(_("Really delete ") + filename + _(" now?"));

So you should either avoid this situation or use `Glib::ustring::compose()` which supports syntax such as:

    std::cout << Glib::ustring::compose(
                 _("Current amount: %1 Future: %2"), amount, future) << std::endl;

    label.set_text(Glib::ustring::compose(_("Really delete %1 now?"), filename));

#### Assuming the displayed size of strings

You never know how much space a string will take on screen when translated. It might very possibly be twice the size of the original English string. Luckily, most gtkmm widgets will expand at runtime to the required size.

#### Palavras incomuns

You should avoid cryptic abbreviations, slang, or jargon. They are usually difficult to translate, and are often difficult for even native speakers to understand.

#### Using non-ASCII characters in strings

Currently, gettext does not support non-ASCII characters (i.e. any characters with a code above 127) in source code. For instance, you cannot use the copyright sign (©).

To work around this, you could write a comment in the source code just before the string, telling the translators to use the special character if it is available in their languages. For English, you could then make an American English `en_US.po` translation which used that special character.

### Getting help with translations

If your program is free software, there is a whole `GNOME` subproject devoted to helping you make translations, the `GNOME` Translation Project.

The way it works is that you upload your source code to a git repository where translators can access it, then file an issue to the damned-lies project and ask to have your program added to the list of modules to translate.

Then you make sure you update the file `POTFILES.in` in the `po/` subdirectory (`intltool-update -m` can help with this) so that the translators always access updated `myprogram.pot` files, and simply freeze the strings at least a couple of days before you make a new release. Depending on the number of strings your program contains and how popular it is, the translations will then start to tick in as `.po` files.

Note that most language teams only consist of 1-3 persons, so if your program contains a lot of strings, it might last a while before anyone has the time to look at it. Also, most translators do not want to waste their time (translating is a very time-consuming task) so if they do not assess your project as being really serious (in the sense that it is polished and being maintained) they may decide to spend their time on some other project.

### Exemplo

Here is a simple example with translatable strings in C++ code. It shows what you can do if you don't use autotools or meson. It is also an example of using the Gtk::TextView widget.

This program can set the locale, if it's specified in a configuration file. This is not normal behavior. Most programs accept the locale that the user has selected, for instance with an environment variable.

Translatable Strings

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

      // Configuration file, showing configured locale.
      static const std::string config_file_name;

    protected:
      void fill_text_tag_table();
      void fill_buffer();

      void on_dropdown_changed();

      // Child widgets
      Gtk::HeaderBar m_HeaderBar;
      Gtk::DropDown m_DropDown;
      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::TextView m_TextView;

      Glib::RefPtr<Gtk::StringList> m_StringList;
      Glib::RefPtr<Gtk::TextTagTable> m_refTextTagTable;
      Glib::RefPtr<Gtk::TextBuffer> m_refTextBuffer;
    };

    #endif // GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <fstream>
    #include <iostream>
    #include <glibmm/i18n.h>

    const std::string ExampleWindow::config_file_name("appconfig.cfg");

    ExampleWindow::ExampleWindow()
    {
      set_title(_("English i18n example"));
      set_default_size(500, 300);

      // Header bar
      m_HeaderBar.set_show_title_buttons(true);
      m_HeaderBar.pack_start(m_DropDown);

      // Set headerbar as titlebar
      set_titlebar(m_HeaderBar);

      // Fill the dropdown
      const std::vector<Glib::ustring> strings{
        "Locale", "en_US.UTF-8", "de_DE.UTF-8", "cs_CZ.UTF-8", "sv_SE.UTF-8"
      };
      m_StringList = Gtk::StringList::create(strings);
      m_DropDown.set_model(m_StringList);
      m_DropDown.set_selected(0);

      m_DropDown.property_selected().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_dropdown_changed));

      // Add the TextView, inside a ScrolledWindow.
      m_ScrolledWindow.set_child(m_TextView);
      set_child(m_ScrolledWindow);

      fill_text_tag_table();
      fill_buffer();
      m_TextView.set_buffer(m_refTextBuffer);
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_dropdown_changed()
    {
      const auto selected = m_DropDown.get_selected();
      const auto text = m_StringList->get_string(selected);
      std::cout << "DropDown changed: " << text << std::endl;
      if (selected > 0)
      {
        std::ofstream myfile;
        myfile.open(config_file_name);
        if (myfile.is_open())
        {
          myfile << text << std::endl;
          myfile.close();
        }
        else
          std::cout << "Could not open file " << config_file_name << std::endl;
      }
    }

    void ExampleWindow::fill_text_tag_table()
    {
      m_refTextTagTable = Gtk::TextTagTable::create();
      auto textTag = Gtk::TextTag::create("plain-text");
      textTag->property_wrap_mode() = Gtk::WrapMode::WORD;
      m_refTextTagTable->add(textTag);

      textTag = Gtk::TextTag::create("script");
      textTag->property_wrap_mode() = Gtk::WrapMode::NONE;
      textTag->property_indent() = 20;
      textTag->property_family() = "Monospace";
      textTag->property_background() = "rgb(92%, 92%, 92%)"; // Light gray
      m_refTextTagTable->add(textTag);
    }

    void ExampleWindow::fill_buffer()
    {
      m_refTextBuffer = Gtk::TextBuffer::create(m_refTextTagTable);

      // Get beginning of buffer; each insertion will revalidate the
      // iterator to point to just after the inserted text.
      auto iter = m_refTextBuffer->begin();

      iter = m_refTextBuffer->insert_with_tag(iter,
        "To build myapp with messages in a different language, e.g. German,"
        " do this in a terminal window:\n\n",
        "plain-text");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "g++ -o myapp main.cc examplewindow.cc `pkg-config --cflags --libs gtkmm-4.0` -std=c++17\n\n",
        "script");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "Before you run myapp, create the files with translated texts:\n\n", "plain-text");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "mkdir po\n"
        "cd po\n"
        "cat >POTFILES.in <<EOF\n"
        "# List of source files containing translatable strings.\n"
        "main.cc\n"
        "examplewindow.cc\n"
        "EOF\n\n", "script");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "Export all quoted texts from source code: _(\"text\") to file myapp.pot:\n\n",
        "plain-text");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "intltool-update --pot --gettext-package myapp\n\n", "script");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "Create the de.po file:\n\n", "plain-text");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "msginit --no-translator --locale de_DE.UTF-8\n\n", "script");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "Now run poedit or some other editor, open file de.po and translate texts of messages."
        " Write the translations after 'msgstr'."
        " If charset is not UTF-8 in the .po file, change to UTF-8."
        " Then save the de.po file. (Later, to update the .po file, use ",
        "plain-text");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "intltool-update de", "script");
      iter = m_refTextBuffer->insert_with_tag(iter,
        ".) Still in the po directory, create myapp.mo from de.po:\n\n", "plain-text");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "mkdir --parents ../locale/de/LC_MESSAGES\n"
        "msgfmt --check --verbose --output-file ../locale/de/LC_MESSAGES/myapp.mo de.po\n\n",
        "script");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "Run myapp with specified language:\n\n", "plain-text");
      iter = m_refTextBuffer->insert_with_tag(iter,
        "cd ..\n"
        "LANG=de_DE.UTF-8 ./myapp\n\n", "script");
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <fstream>
    #include <iostream>
    #include <string>
    #include <locale>
    #include <clocale>
    #include <glibmm/i18n.h>

    const char* GETTEXT_PACKAGE = "myapp";
    const char* PROGRAMNAME_LOCALEDIR = "locale";

    int main(int argc, char* argv[])
    {
      std::ifstream myfile(ExampleWindow::config_file_name);
      if (myfile.is_open())
      {
        // Set the configured locale.
        std::string line;
        std::getline(myfile, line);
        std::cout <<"Preference settings: "<< line << std::endl;
        // Don't use the user's preferred locale.
        Glib::set_init_to_users_preferred_locale(false);
        Glib::setenv("LANG", line, true);
        std::cout << "getenv(LANG)= " << Glib::getenv("LANG") << '\n';
        std::setlocale(LC_ALL, line.c_str());
        myfile.close();
      }
      // If the configuration file does not exist, the user's preferred locale is used.

      bindtextdomain(GETTEXT_PACKAGE, PROGRAMNAME_LOCALEDIR);
      bind_textdomain_codeset(GETTEXT_PACKAGE, "UTF-8");
      textdomain(GETTEXT_PACKAGE);

      // Gtk::Application::create() calls Glib::init(), which sets the C++ global locale.
      auto app = Gtk::Application::create("org.gtkmm.example");

      // On startup, when std::cout is created, the global locale is the "C" locale,
      // AKA the classic locale.
      std::cout << _("English App is Running") << ", "
        << std::cout.getloc().name() << " locale: " << 1234.56 << '\n';

      // Use the new global locale for future output to std::cout.
      std::cout.imbue(std::locale());

      std::cout << _("English App is Running") << ", "
        << std::cout.getloc().name() << " locale: " << 1234.56 << '\n';
      std::cout << "Force unicode German text: Gr\xC3\xBC\xC3\x9F Gott\n";

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

## Widgets personalizados

gtkmm makes it very easy to derive new widgets by inheriting from an existing widget class, either by deriving from a container and adding child widgets, or by deriving from a single-item widget, and changing its behavior. But you might occasionally find that no suitable starting point already exists. In this case, you can implement a widget from scratch.

### Contêiners personalizados

When deriving a custom container widget directly from Gtk::Widget, you should override the following virtual methods:

- get_request_mode_vfunc(): Return what `Gtk::SizeRequestMode` is preferred by the container.

- measure_vfunc(): Calculate the minimum and natural width or height of the container.

- size_allocate_vfunc(): Position the child widgets, given the height and width that the container has actually been given.

The get_request_mode_vfunc(), measure_vfunc(), and size_allocate_vfunc() virtual methods control the layout of the child widgets. For instance, if your container has 2 child widgets, with one below the other, your get_request_mode_vfunc() might request height-for-width layout. Then your measure_vfunc() might report the maximum of the widths of the child widgets when asked to report width, and it might report the sum of their heights when asked to report height. If you want padding between the child widgets then you would add that to the width and height too. Your widget's container will use this result to ensure that your widget gets enough space, and not less. By examining each widget's parent, and its parent, this logic will eventually decide the size of the top-level window.

You are not guaranteed to get the `Gtk::SizeRequestMode` that you request. Therefore measure_vfunc() must return sensible values for all reasonable values of its input parameters. For a description of measure_vfunc()'s parameters see also the description of Gtk::Widget::measure(), which may be better documented than measure_vfunc().

size_allocate_vfunc() receives the actual height and width that the parent container has decided to give to your widget. This might be more than the minimum, or even more than the natural size, for instance if the top-level window has been expanded. You might choose to ignore the extra space and leave a blank area, or you might choose to expand your child widgets to fill the space, or you might choose to expand the padding between your widgets. It's your container, so you decide.

Your container must unparent its children before the underlying C object (a gtkmm__GtkWidget) is finalized. If your container is used as a managed widget, it shall unparent its children in a Gtk::Widget::signal_destroy() handler (available since gtkmm 4.8). If your container is not managed, that signal handler is not called. Instead the children shall be unparented in the C++ destructor. If you want your container to be useful both ways, unparent the children both in the destructor and in a signal handler. See the example code.

#### Exemplo

This example implements a container with child widgets, one above the other. Of course, in this case it would be far simpler just to use a vertical Gtk::Box or Gtk::Grid.

Contêiner personalizado

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>
    #include "mycontainer.h"

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      //Signal handlers:
      void on_button_quit();

      //Child widgets:
      Gtk::Box m_VBox;
      MyContainer m_MyContainer;
      Gtk::Button m_Button_Child;
      Gtk::Label m_Label_Child;
      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `mycontainer.h` (For use with gtkmm 4)

    #ifndef GTKMM_CUSTOM_CONTAINER_MYCONTAINER_H
    #define GTKMM_CUSTOM_CONTAINER_MYCONTAINER_H

    #include <gtkmm/widget.h>
    #include <gtkmm/version.h>

    #define HAS_SIGNAL_DESTROY GTKMM_CHECK_VERSION(4,7,1)

    class MyContainer : public Gtk::Widget
    {
    public:
      MyContainer();
      ~MyContainer() override;

      void append(Gtk::Widget& child);
      void prepend(Gtk::Widget& child);
      void remove(Gtk::Widget& child);

    protected:
      int get_nvis_children() const;

      //Overrides:
      Gtk::SizeRequestMode get_request_mode_vfunc() const override;
      void measure_vfunc(Gtk::Orientation orientation, int for_size, int& minimum, int& natural,
        int& minimum_baseline, int& natural_baseline) const override;
      void size_allocate_vfunc(int width, int height, int baseline) override;

    #if HAS_SIGNAL_DESTROY
      // Signal handler:
      void on_container_destroy();
    #endif
    };

    #endif //GTKMM_CUSTOM_CONTAINER_MYCONTAINER_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Child("Child button"),
      m_Label_Child("Child label", Gtk::Align::END, Gtk::Align::CENTER),
      m_Button_Quit("Quit")
    {
      set_title("Custom Container example");
      set_default_size(400, 200);

      m_VBox.set_margin(6);
      set_child(m_VBox);

      //Add the child widgets to the custom container:
      m_MyContainer.append(m_Button_Child);
      m_MyContainer.append(m_Label_Child);
      m_MyContainer.prepend(*Gtk::make_managed<Gtk::Label>(
        "First line\nSecond line\nThird line"));
      m_MyContainer.set_expand();
      m_VBox.append(m_MyContainer);

    #if HAS_SIGNAL_DESTROY
      // A managed custom container.
      auto container = Gtk::make_managed<MyContainer>();
      container->prepend(*Gtk::make_managed<Gtk::Label>("Second custom container"));
      container->set_expand();
      m_VBox.append(*container);
    #endif
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(6);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_button_quit) );
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `mycontainer.cc` (For use with gtkmm 4)

    #include "mycontainer.h"

    #include <algorithm> // std::max()

    // This example container is a simplified vertical Box.
    //
    // It can't be used as a managed widget, managed by another container
    // unless Gtk::Widget::signal_destroy() exists.
    // It would cause an error like
    // Gtk-WARNING **: 08:31:48.137: Finalizing gtkmm__GtkWidget 0x561b777462c0, but it still has children left:

    MyContainer::MyContainer()
    {
    #if HAS_SIGNAL_DESTROY
      signal_destroy().connect(sigc::mem_fun(*this, &MyContainer::on_container_destroy));
    #endif
    }

    MyContainer::~MyContainer()
    {
      // If MyContainer is a managed widget, the underlying C object is destructed
      // before this C++ destructor is executed.
      if (!gobj())
        return;

      // If MyContainer is not a managed widget, unparent all children here.
      while (Widget* child = get_first_child())
        child->unparent();
    }

    #if HAS_SIGNAL_DESTROY
    // This signal handler is called only if MyContainer is a managed widget.
    void MyContainer::on_container_destroy()
    {
      while (Widget* child = get_first_child())
        child->unparent();
    }
    #endif

    // Get number of visible children.
    int MyContainer::get_nvis_children() const
    {
      int nvis_children = 0;
      for (const Widget* child = get_first_child(); child; child = child->get_next_sibling())
        if (child->get_visible())
          ++nvis_children;

      return nvis_children;
    }

    Gtk::SizeRequestMode MyContainer::get_request_mode_vfunc() const
    {
      return Gtk::SizeRequestMode::HEIGHT_FOR_WIDTH;
    }

    // Discover the total amount of minimum space and natural space needed by
    // this container and its children.
    void MyContainer::measure_vfunc(Gtk::Orientation orientation, int for_size,
      int& minimum, int& natural, int& minimum_baseline, int& natural_baseline) const
    {
      // Don't use baseline alignment.
      minimum_baseline = -1;
      natural_baseline = -1;

      minimum = 0;
      natural = 0;

      // Number of visible children.
      const int nvis_children = get_nvis_children();

      if (orientation == Gtk::Orientation::HORIZONTAL)
      {
        // Divide the height equally among the visible children.
        if (for_size > 0 && nvis_children > 0)
          for_size /= nvis_children;

        // Request a width equal to the width of the widest visible child.
      }

      for (const Widget* child = get_first_child(); child; child = child->get_next_sibling())
        if (child->get_visible())
        {
          int child_minimum, child_natural, ignore;
          child->measure(orientation, for_size, child_minimum, child_natural, ignore, ignore);
          minimum = std::max(minimum, child_minimum);
          natural = std::max(natural, child_natural);
        }

      if (orientation == Gtk::Orientation::VERTICAL)
      {
        // The allocated height will be divided equally among the visible children.
        // Request a height equal to the number of visible children times the height
        // of the highest child.
        minimum *= nvis_children;
        natural *= nvis_children;
      }
    }

    void MyContainer::size_allocate_vfunc(int width, int height, int baseline)
    {
      //Do something with the space that we have actually been given:
      //(We will not be given heights or widths less than we have requested, though
      //we might get more.)

      // Number of visible children.
      const int nvis_children = get_nvis_children();

      if (nvis_children <= 0)
      {
        // No visible child.
        return;
      }

      //Assign space to the children:
      Gtk::Allocation child_allocation;
      const int height_per_child = height / nvis_children;

      //Place the first visible child at the top-left:
      child_allocation.set_x(0);
      child_allocation.set_y(0);

      //Make it take up the full width available:
      child_allocation.set_width(width);
      child_allocation.set_height(height_per_child);

      //Divide the height equally among the visible children.
      for (Widget* child = get_first_child(); child; child = child->get_next_sibling())
        if (child->get_visible())
        {
          child->size_allocate(child_allocation, baseline);
          child_allocation.set_y(child_allocation.get_y() + height_per_child);
        }
    }

    void MyContainer::append(Gtk::Widget& child)
    {
       child.insert_at_end(*this);
    }

    void MyContainer::prepend(Gtk::Widget& child)
    {
       child.insert_at_start(*this);
    }

    void MyContainer::remove(Gtk::Widget& child)
    {
      child.unparent();
    }

### Widgets personalizados

By deriving directly from Gtk::Widget you can do all the drawing for your widget directly, instead of just arranging child widgets. For instance, a Gtk::Label draws the text of the label, but does not do this by using other widgets.

When deriving from Gtk::Widget, you should override the following virtual methods. The methods marked (optional) need not be overridden in all custom widgets. The base class's methods may be appropriate.

- get_request_mode_vfunc(): (optional) Return what `Gtk::SizeRequestMode` is preferred by the widget.

- measure_vfunc(): Calculate the minimum and natural width or height of the widget.

- size_allocate_vfunc(): (optional) Position the widget, given the height and width that it has actually been given.

- on_realize(): (optional)

- on_unrealize(): (optional)

- on_map(): (optional)

- on_unmap(): (optional)

- snapshot_vfunc(): Create a render node, e.g. a Cairo::Context node, and draw on it.

The first 3 methods in the previous table are also overridden in custom containers. They are briefly described in the Custom Containers section.

#### Class Init and Instance Init Functions

Some GTK functions, if called at all, must be called from the class init function. Some other GTK functions, if called, must be called from the instance init function. If your custom widget must call any of those functions, you can derive a class from Glib::ExtraClassInit and derive your custom class from that class. The custom CSS name example shows how that's done.

#### Exemplo

This example implements a widget which draws Penrose triangles.

Widget personalizado

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>
    #include "mywidget.h"

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      void on_button_quit();

      //Child widgets:
      Gtk::Grid m_Grid;
      MyWidget m_MyWidgetS1;
      MyWidget m_MyWidgetS2;
      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `mywidget.h` (For use with gtkmm 4)

    #ifndef GTKMM_CUSTOM_WIDGET_MYWIDGET_H
    #define GTKMM_CUSTOM_WIDGET_MYWIDGET_H

    #include <gtkmm/widget.h>
    #include <gtkmm/border.h>
    #include <gdkmm/rgba.h>

    class MyWidget : public Gtk::Widget
    {
    public:
      MyWidget();
      ~MyWidget() override;

    protected:
      // Overrides:
      Gtk::SizeRequestMode get_request_mode_vfunc() const override;
      void measure_vfunc(Gtk::Orientation orientation, int for_size, int& minimum, int& natural,
        int& minimum_baseline, int& natural_baseline) const override;
      void on_map() override;
      void on_unmap() override;
      void on_realize() override;
      void on_unrealize() override;
      void snapshot_vfunc(const Glib::RefPtr<Gtk::Snapshot>& snapshot) override;

      Gtk::Border m_padding;
      Gdk::RGBA m_foreground{0.0, 0.0, 1.0};
      Gdk::RGBA m_background{1.0, 0.0, 0.0};
    };

    #endif //GTKMM_CUSTOM_WIDGET_MYWIDGET_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_Button_Quit("Quit")
    {
      set_title("Custom Widget example");
      set_default_size(600, 400);

      m_Grid.set_margin(6);
      m_Grid.set_row_spacing(10);
      m_Grid.set_column_spacing(10);

      set_child(m_Grid);

      m_Grid.attach(m_MyWidgetS1, 0, 0);
      m_Grid.attach(m_MyWidgetS2, 1, 1);

      m_Grid.attach(m_ButtonBox, 0, 2, 2, 1);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(6);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect( sigc::mem_fun(*this, &ExampleWindow::on_button_quit) );
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char *argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `mywidget.cc` (For use with gtkmm 4)

    #include "mywidget.h"
    #include <gdkmm/general.h>  // for Gdk::Cairo:: functions
    #include <gtkmm/snapshot.h>

    MyWidget::MyWidget()
    {
      // Expand, if there is extra space.
      set_expand(true);

      m_padding.set_left(5);
      m_padding.set_right(15);
      m_padding.set_top(10);
      m_padding.set_bottom(20);
    }

    MyWidget::~MyWidget()
    {
    }

    Gtk::SizeRequestMode MyWidget::get_request_mode_vfunc() const
    {
      //Accept the default value supplied by the base class.
      return Gtk::Widget::get_request_mode_vfunc();
    }

    //Discover the total amount of minimum space and natural space needed by
    //this widget.
    //Let's make this simple example widget always need minimum 60 by 50 and
    //natural 100 by 70.
    void MyWidget::measure_vfunc(Gtk::Orientation orientation, int /* for_size */,
      int& minimum, int& natural, int& minimum_baseline, int& natural_baseline) const
    {
      if (orientation == Gtk::Orientation::HORIZONTAL)
      {
        minimum = 60;
        natural = 100;
      }
      else
      {
        minimum = 50;
        natural = 70;
      }

      // Don't use baseline alignment.
      minimum_baseline = -1;
      natural_baseline = -1;
    }

    void MyWidget::on_map()
    {
      //Call base class:
      Gtk::Widget::on_map();
    }

    void MyWidget::on_unmap()
    {
      //Call base class:
      Gtk::Widget::on_unmap();
    }

    void MyWidget::on_realize()
    {
      //Call base class:
      Gtk::Widget::on_realize();
    }

    void MyWidget::on_unrealize()
    {
      //Call base class:
      Gtk::Widget::on_unrealize();
    }

    void MyWidget::snapshot_vfunc(const Glib::RefPtr<Gtk::Snapshot>& snapshot)
    {
      const auto allocation = get_allocation();
      const Gdk::Rectangle rect(0, 0, allocation.get_width(), allocation.get_height());

      // Create a cairo context to draw on.
      auto cr = snapshot->append_cairo(rect);

      // paint the background
      Gdk::Cairo::set_source_rgba(cr, m_background);
      Gdk::Cairo::add_rectangle_to_path(cr, rect);
      cr->fill();

      // draw the foreground
      const double scale_x = 0.001 * (allocation.get_width() - m_padding.get_left() - m_padding.get_right());
      const double scale_y = 0.001 * (allocation.get_height() - m_padding.get_top() - m_padding.get_bottom());
      Gdk::Cairo::set_source_rgba(cr, m_foreground);
      cr->translate(m_padding.get_left(), m_padding.get_top());
      cr->rectangle(0.0, 0.0, 1000.0*scale_x, 1000.0*scale_y);
      cr->move_to(155.*scale_x, 165.*scale_y);
      cr->line_to(155.*scale_x, 838.*scale_y);
      cr->line_to(265.*scale_x, 900.*scale_y);
      cr->line_to(849.*scale_x, 564.*scale_y);
      cr->line_to(849.*scale_x, 438.*scale_y);
      cr->line_to(265.*scale_x, 100.*scale_y);
      cr->line_to(155.*scale_x, 165.*scale_y);
      cr->move_to(265.*scale_x, 100.*scale_y);
      cr->line_to(265.*scale_x, 652.*scale_y);
      cr->line_to(526.*scale_x, 502.*scale_y);
      cr->move_to(369.*scale_x, 411.*scale_y);
      cr->line_to(633.*scale_x, 564.*scale_y);
      cr->move_to(369.*scale_x, 286.*scale_y);
      cr->line_to(369.*scale_x, 592.*scale_y);
      cr->move_to(369.*scale_x, 286.*scale_y);
      cr->line_to(849.*scale_x, 564.*scale_y);
      cr->move_to(633.*scale_x, 564.*scale_y);
      cr->line_to(155.*scale_x, 838.*scale_y);
      cr->stroke();
    }

### Custom CSS Names

Many aspects of the look of widgets are controlled by CSS (Cascading Style Sheet) files. With CSS files you can choose color, font, line thickness, etc. If you give some widgets their own names or their own CSS classes, you can define CSS rules that apply only to those widgets, for instance certain buttons, without affecting other similar widgets.

#### CSS Node Name, Widget Name, CSS Class Name

There are three ways of referring from a widget to data in a CSS file:

- gtk_widget_class_set_css_name() can only be called from the class init function. It sets the CSS node name of all instances of a class (a GType). See the Class Init and Instance Init Functions section.

- Gtk::Widget::set_name() can be called from a C++ constructor. It sets the name of a widget instance.

- Gtk::Widget::add_class_name() can be called from a C++ constructor. It adds the name of a CSS class, used by a widget instance.

The following example shows a button with its own CSS node name, a label with a widget name and a label that uses its own CSS class.

#### Custom Style Information

To add a style sheet to an application, use one of the Gtk::CssProvider::load_from_*() methods. Then add it with Gtk::StyleProvider::add_provider_for_display() (available since gtkmm 4.10) or Gtk::StyleContext::add_provider_for_display(). Gtk::StyleContext also contains methods to read some style information, but this class is deprecated since gtkmm 4.10.

CSS files are described in the documentation of GTK.

#### Exemplo

This example implements a button and two labels with custom style information.

Custom CSS Name

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>
    #include "mybutton.h"

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      ~ExampleWindow() override;

    protected:
      // Signal handlers:
      void on_button_quit();
      static void on_parsing_error(const Glib::RefPtr<const Gtk::CssSection>& section,
        const Glib::Error& error);

      // Child widgets:
      Gtk::Box m_VBox;
      MyButton m_Button_Child;
      Gtk::Label m_Label_Child1;
      Gtk::Label m_Label_Child2;
      Gtk::Box m_ButtonBox;
      Gtk::Button m_Button_Quit;

      Glib::RefPtr<Gtk::CssProvider> m_refCssProvider;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `mybutton.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_MYBUTTON_H
    #define GTKMM_EXAMPLE_MYBUTTON_H

    #include <gtkmm/button.h>
    #include "myextrainit.h"

    class MyButton : public MyExtraInit, public Gtk::Button
    {
    public:
      MyButton(const Glib::ustring& label, bool mnemonic=false);
      ~MyButton() override;
    };

    #endif //GTKMM_EXAMPLE_MYBUTTON_H

File: `myextrainit.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_MYEXTRAINIT_H
    #define GTKMM_EXAMPLE_MYEXTRAINIT_H

    #include <glibmm/extraclassinit.h>
    #include <glibmm/ustring.h>

    // Calls gtk_widget_class_set_css_name() in the class init function.
    class MyExtraInit : public Glib::ExtraClassInit
    {
    public:
      MyExtraInit(const Glib::ustring& css_name);

    private:
      Glib::ustring m_css_name;
    };

    #endif //GTKMM_EXAMPLE_MYEXTRAINIT_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>
    #include <gtkmm/version.h>

    #define HAS_STYLE_PROVIDER_ADD_PROVIDER_FOR_DISPLAY GTKMM_CHECK_VERSION(4,9,1)

    ExampleWindow::ExampleWindow()
    : m_VBox(Gtk::Orientation::VERTICAL),
      m_Button_Child("Button with custom CSS node name"),
      m_Label_Child1("Label with custom name"),
      m_Label_Child2("Label with custom CSS class"),
      m_Button_Quit("Quit")
    {
      set_title("Custom CSS name example");
      set_default_size(400, 200);

      m_VBox.set_margin(10);
      m_VBox.set_spacing(5);
      set_child(m_VBox);

      // There are 3 ways to set custom CSS data for a widget:
      // 1. The CSS name can be set for a GType with gtk_widget_class_set_css_name().
      // 2. The CSS name can be set for a widget instance with gtk_widget_set_name()
      //    (Gtk::Widget::set_name()).
      // 3. A CSS class can be set for a widget instance with
      //    gtk_widget_add_css_class() (Gtk::Widget::add_css_class()).
      //
      // gtk_widget_class_set_css_name(), if used, must be called in the class init
      // function. It has not been wrapped in a C++ function.
      // Gtk::Widget::set_name() and Gtk::Widget::add_css_class() can be called in
      // a C++ constructor.

      // CSS widget name, which must be used in the CSS file, preceded by "#".
      m_Label_Child1.set_name("my-label1");

      // CSS class name, which must be used in the CSS file, preceded by ".".
      m_Label_Child2.add_css_class("my-label2");

      // Add the child widgets to m_VBox:
      m_VBox.append(*Gtk::make_managed<Gtk::Label>("Ordinary label"));
      m_VBox.append(m_Button_Child);
      m_VBox.append(m_Label_Child1);
      m_VBox.append(m_Label_Child2);
      m_VBox.set_expand();
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_Button_Quit);
      m_ButtonBox.set_margin(6);
      m_Button_Quit.set_hexpand(true);
      m_Button_Quit.set_halign(Gtk::Align::END);
      m_Button_Quit.signal_clicked().connect( sigc::mem_fun(*this,
                  &ExampleWindow::on_button_quit) );

      // Load extra CSS file.
      m_refCssProvider = Gtk::CssProvider::create();
    #if HAS_STYLE_PROVIDER_ADD_PROVIDER_FOR_DISPLAY
      Gtk::StyleProvider::add_provider_for_display(get_display(), m_refCssProvider,
        GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
    #else
      Gtk::StyleContext::add_provider_for_display(get_display(), m_refCssProvider,
        GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
    #endif

      m_refCssProvider->signal_parsing_error().connect(
        [](const auto& section, const auto& error)
        { on_parsing_error(section, error); }
      );
      m_refCssProvider->load_from_path("custom_gtkmm.css");
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      close();
    }

    void ExampleWindow::on_parsing_error(const Glib::RefPtr<const Gtk::CssSection>& section,
      const Glib::Error& error)
    {
      std::cerr << "on_parsing_error(): " << error.what() << std::endl;
      if (section)
      {
        const auto file = section->get_file();
        if (file)
        {
          std::cerr << "  URI = " << file->get_uri() << std::endl;
        }

        auto start_location = section->get_start_location();
        auto end_location = section->get_end_location();
        std::cerr << "  start_line = " << start_location.get_lines()+1
                  << ", end_line = " << end_location.get_lines()+1 << std::endl;
        std::cerr << "  start_position = " << start_location.get_line_chars()
                  << ", end_position = " << end_location.get_line_chars() << std::endl;
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      // Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

File: `mybutton.cc` (For use with gtkmm 4)

    #include "mybutton.h"
    #include <gtk/gtk.h> // For GTK_IS_BUTTON()
    #include <iostream>

    MyButton::MyButton(const Glib::ustring& label, bool mnemonic)
      :
      // The GType name will actually be gtkmm__CustomObject_MyButton
      Glib::ObjectBase("MyButton"),
      MyExtraInit("my-button"), // CSS node name, which must be used in the CSS file.
      Gtk::Button(label, mnemonic)
    {
      // This shows the GType name:
      std::cout << "GType name: " << G_OBJECT_TYPE_NAME(gobj()) << std::endl;

      // This shows that the GType still derives from GtkButton:
      std::cout << "Gtype is a GtkButton?: " << GTK_IS_BUTTON(gobj()) << std::endl;

      // The CSS name can be set either
      // - for a GType (in this case for your custom class) with gtk_widget_class_set_css_name(), or
      // - for a widget instance with gtk_widget_set_name() (Gtk::Widget::set_name()).
      //
      // gtk_widget_class_set_css_name(), if used, must be called in the class init function.
      // It has not been wrapped in a C++ function.
      // Gtk::Widget::set_name() can be called in a C++ constructor.
      //
      // Another alternative: The custom button inherits the CSS name "button" from
      // GtkButton. That name can be used in the CSS file.
    }

    MyButton::~MyButton()
    {
    }

File: `myextrainit.cc` (For use with gtkmm 4)

    #include "myextrainit.h"
    #include <gtkmm/widget.h>
    #include <gtk/gtk.h>

    namespace
    {
    using BaseObjectType = GtkWidget;
    using BaseClassType = GtkWidgetClass;

    // These callback functions are called from GLib (a C library).
    // They shall have C linkage. (Many compilers accept callback functions
    // with C++ linkage, but such a program has undefined behavior.)
    //
    // If you want the functions with C linkage to have internal linkage,
    // they must be declared 'static', even though they are defined in an anonymous
    // namespace. The compiler respects namespace declarations of functions
    // with C linkage, but the linker does not.
    extern "C"
    {
    // Extra class init function.
    static void class_init_function(void* g_class, void* class_data)
    {
      g_return_if_fail(GTK_IS_WIDGET_CLASS(g_class));

      const auto klass = static_cast<BaseClassType*>(g_class);
      const auto css_name = static_cast<Glib::ustring*>(class_data);

      gtk_widget_class_set_css_name(klass, css_name->c_str());
    }

    // Extra instance init function.
    static void instance_init_function(GTypeInstance* instance, void* /* g_class */)
    {
      g_return_if_fail(GTK_IS_WIDGET(instance));

      // Nothing to do here.
      // This extra instance init function just shows how such a function can
      // be added to a custom widget, if necessary.
    }
    } // extern "C"
    } // anonymous namespace

    MyExtraInit::MyExtraInit(const Glib::ustring& css_name)
    :
    Glib::ExtraClassInit(class_init_function, &m_css_name, instance_init_function),
    m_css_name(css_name)
    {
    }

File: `custom_gtkmm.css` (For use with gtkmm 4)

    /* Example of a CSS style sheet. */

    my-button {
      background-color: red;
      color:            blue;
      padding:          10px 15px 20px 5px; /* top right bottom left */
      border:           solid black 2px;
      border-radius:    8px;
    }
    my-button:active {
      background-color: rgb(0,255,0);
    }
    #my-label1 {
      background-color: rgb(180,180,180);
      color:            rgb(0,255,255);
      padding:          10px 15px 10px 25px; /* top right bottom left */
    }
    #my-label1:hover {
      background-color: rgb(220,220,220);
    }
    .my-label2 {
      background-color: rgb(180,180,100);
      color:            black;
      padding:          5px 15px 5px 25px; /* top right bottom left */
    }
    .my-label2:hover {
      background-color: rgb(220,220,140);
    }

## Programas com várias linhas de processamento

### The constraints

Care is required when writing programs based on gtkmm using multiple threads of execution, arising from the fact that libsigc++, and in particular sigc::trackable, are not thread-safe. That's because none of the complex interactions that occur behind the scenes when using libsigc++ are protected by a mutex or other means of synchronization.

These interactions arise from the fact that, amongst other things, a class inheriting from sigc::trackable will, via that inheritance, have a std::list object keeping track of slots created by calls to `sigc::mem_fun()` representing any of its non-static methods (more particularly it keeps a list of callbacks which will null the connected slots on its destruction). Each sigc::slot object also keeps, via sigc::slot_rep, its own sigc::trackable object to track any sigc::connection objects which it needs to inform about its demise, and also has a function to deregister itself from any sigc::trackable on disconnection or destruction. sigc::signal objects also keep lists of slots, which will be updated by a call to their connect() method or calls to any sigc::connection object relating to such a connection.

#### As regras

This requires a number of rules to be observed when writing multi-threaded programs using gtkmm. These are set out below, but one point to note is that extra care is required when deriving classes from sigc::trackable, because the effects are unintuitive (see particularly points 4 and 5 below).

1. Use Glib::Dispatcher to invoke gtkmm functions from worker threads (this is dealt with in more detail in the next section).

2. A sigc::signal object should be regarded as owned by the thread which created it. Only that thread should connect a sigc::slot object to the signal object, and only that thread should emit() or call operator()() on the signal, or null any connected sigc::slot object. It follows (amongst other things) that any signal object provided by a gtkmm widget should only be operated on in the main GUI thread and any object deriving from sigc::trackable having its non-static methods referenced by slots connected to the signal object should only be destroyed in that thread.

3. Any sigc::connection object should be regarded as owned by the thread in which the method returning the sigc::connection object was called. Only that thread should call sigc::connection methods on the object.

4. A sigc::slot object created by a call to `sigc::mem_fun()` which references a method of a class deriving from sigc::trackable should never be copied to another thread, nor destroyed by a different thread than the one which created it.

5. If a particular class object derives from sigc::trackable, only one thread should create sigc::slot objects representing any of the class's non-static methods by calling `sigc::mem_fun()`. The first thread to create such a slot should be regarded as owning the relevant object for the purpose of creating further slots referencing any of its non-static methods using that function, or nulling those slots by disconnecting them or destroying the trackable object.

6. Although glib is itself thread-safe, any glibmm wrappers which use libsigc++ will not be. So for example, only the thread in which a main loop runs should call Glib::SignalIdle::connect(), Glib::SignalIO::connect(), Glib::SignalTimeout::connect(), Glib::SignalTimeout::connect_seconds for that main loop, or manipulate any sigc::connection object returned by them.

   The connect*_once() variants, Glib::SignalIdle::connect_once(), Glib::SignalTimeout::connect_once(), Glib::SignalTimeout::connect_seconds_once(), are thread-safe for any case where the slot is not created by a call to `sigc::mem_fun()` which represents a method of a class deriving from sigc::trackable.

### Using Glib::Dispatcher

The slots connected to sigc::signal objects execute in the thread which calls emit() or operator()() on the signal. Glib::Dispatcher does not behave this way: instead its connected slots execute in the thread in which the Glib::Dispatcher object was constructed (which must have a glib main loop). If a Glib::Dispatcher object is constructed in the main GUI thread (which will therefore be the receiver thread), any worker thread can emit on it and have the connected slots safely execute gtkmm functions.

Some thread safety rules on the use of Glib::Dispatcher still apply. As mentioned, a Glib::Dispatcher object must be constructed in the receiver thread (the thread in whose main loop it will execute its connected slots). By default this is the main program thread, although there is a Glib::Dispatcher constructor which can take the Glib::MainContext object of any thread which has a main loop. Only the receiver thread should call connect() on the Glib::Dispatcher object, or manipulate any related sigc::connection object, unless additional synchronization is employed. However, any worker thread can safely emit on the Glib::Dispatcher object without any locking once the receiver thread has connected the slots, provided that it is constructed before the worker thread is started (if it is constructed after the thread has started, additional synchronization will normally be required to ensure visibility).

Aside from the fact that connected slots always execute in the receiver thread, Glib::Dispatcher objects are similar to sigc::signal<void()> objects. They therefore cannot pass unbound arguments nor return a value. The best way to pass unbound arguments is with a thread-safe (asynchronous) queue. At the time of writing glibmm does not have one, although most people writing multi-threaded code will have one available to them (they are relatively easy to write although there are subtleties in combining thread safety with strong exception safety).

A Glib::Dispatcher object can be emitted on by the receiver thread as well as by a worker thread, although this should be done within reasonable bounds. On unix-like systems Glib::Dispatcher objects share a single common pipe, which could in theory at least fill up on a very heavily loaded system running a program with a very large number of Dispatcher objects in use. Were the pipe to fill up before the receiver thread's main loop has had an opportunity to read from it to empty it, and the receiver thread attempt to emit and so write to it when it is in that condition, the receiver thread would block on the write, so deadlocking. Where the receiver thread is to emit, a normal sigc::signal<void()> object could of course be used instead.

### Exemplo

This is an example program with two threads, one GUI thread, like in all gtkmm programs, and one worker thread. The worker thread is created when you press the `Start work` button. It is deleted when the work is finished, when you press the `Stop work` button, or when you press the `Quit` button.

A Glib::Dispatcher is used for sending notifications from the worker thread to the GUI thread. The ExampleWorker class contains data which is accessed by both threads. This data is protected by a std::mutex. Only the GUI thread updates the GUI.

Compiling and linking a multi-threaded program can require special compiler and linker options. If you use the g++ compiler, add the `-pthread` option. Other compilers may require other options. If you build with meson, it handles the multi-threading complications for you, if you add `dependency('threads')`.

Multi-Threaded Program

Source Code

File: `examplewindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>
    #include "exampleworker.h"

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();

      // Called from the worker thread.
      void notify();

    private:
      // Signal handlers.
      void on_start_button_clicked();
      void on_stop_button_clicked();
      void on_quit_button_clicked();

      void update_start_stop_buttons();
      void update_widgets();

      // Dispatcher handler.
      void on_notification_from_worker_thread();

      // Member data.
      Gtk::Box m_VBox;
      Gtk::Box m_ButtonBox;
      Gtk::Button m_ButtonStart;
      Gtk::Button m_ButtonStop;
      Gtk::Button m_ButtonQuit;
      Gtk::ProgressBar m_ProgressBar;
      Gtk::ScrolledWindow m_ScrolledWindow;
      Gtk::TextView m_TextView;

      Glib::Dispatcher m_Dispatcher;
      ExampleWorker m_Worker;
      std::thread* m_WorkerThread;
    };

    #endif // GTKMM_EXAMPLEWINDOW_H

File: `exampleworker.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEWORKER_H
    #define GTKMM_EXAMPLEWORKER_H

    #include <gtkmm.h>
    #include <thread>
    #include <mutex>

    class ExampleWindow;

    class ExampleWorker
    {
    public:
      ExampleWorker();

      // Thread function.
      void do_work(ExampleWindow* caller);

      void get_data(double* fraction_done, Glib::ustring* message) const;
      void stop_work();
      bool has_stopped() const;

    private:
      // Synchronizes access to member data.
      mutable std::mutex m_Mutex;

      // Data used by both GUI thread and worker thread.
      bool m_shall_stop;
      bool m_has_stopped;
      double m_fraction_done;
      Glib::ustring m_message;
    };

    #endif // GTKMM_EXAMPLEWORKER_H

File: `examplewindow.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <iostream>

    ExampleWindow::ExampleWindow() :
      m_VBox(Gtk::Orientation::VERTICAL, 5),
      m_ButtonBox(Gtk::Orientation::HORIZONTAL),
      m_ButtonStart("Start work"),
      m_ButtonStop("Stop work"),
      m_ButtonQuit("_Quit", /* mnemonic= */ true),
      m_ProgressBar(),
      m_ScrolledWindow(),
      m_TextView(),
      m_Dispatcher(),
      m_Worker(),
      m_WorkerThread(nullptr)
    {
      set_title("Multi-threaded example");
      set_default_size(300, 300);

      m_VBox.set_margin(5);
      set_child(m_VBox);

      // Add the ProgressBar.
      m_VBox.append(m_ProgressBar);

      m_ProgressBar.set_text("Fraction done");
      m_ProgressBar.set_show_text();

      // Add the TextView, inside a ScrolledWindow.
      m_ScrolledWindow.set_child(m_TextView);

      // Only show the scrollbars when they are necessary.
      m_ScrolledWindow.set_policy(Gtk::PolicyType::AUTOMATIC, Gtk::PolicyType::AUTOMATIC);
      m_ScrolledWindow.set_expand();

      m_VBox.append(m_ScrolledWindow);

      m_TextView.set_editable(false);

      // Add the buttons to the ButtonBox.
      m_VBox.append(m_ButtonBox);

      m_ButtonBox.append(m_ButtonStart);
      m_ButtonBox.append(m_ButtonStop);
      m_ButtonBox.append(m_ButtonQuit);
      m_ButtonBox.set_margin(5);
      m_ButtonBox.set_spacing(5);
      m_ButtonStart.set_hexpand(true);
      m_ButtonStart.set_halign(Gtk::Align::END);

      // Connect the signal handlers to the buttons.
      m_ButtonStart.signal_clicked().connect(sigc::mem_fun(*this, &ExampleWindow::on_start_button_clicked));
      m_ButtonStop.signal_clicked().connect(sigc::mem_fun(*this, &ExampleWindow::on_stop_button_clicked));
      m_ButtonQuit.signal_clicked().connect(sigc::mem_fun(*this, &ExampleWindow::on_quit_button_clicked));

      // Connect the handler to the dispatcher.
      m_Dispatcher.connect(sigc::mem_fun(*this, &ExampleWindow::on_notification_from_worker_thread));

      // Create a text buffer mark for use in update_widgets().
      auto buffer = m_TextView.get_buffer();
      buffer->create_mark("last_line", buffer->end(), /* left_gravity= */ true);

      update_start_stop_buttons();
    }

    void ExampleWindow::on_start_button_clicked()
    {
      if (m_WorkerThread)
      {
        std::cout << "Can't start a worker thread while another one is running." << std::endl;
      }
      else
      {
        // Start a new worker thread.
        m_WorkerThread = new std::thread(
          [this]
          {
            m_Worker.do_work(this);
          });
      }
      update_start_stop_buttons();
    }

    void ExampleWindow::on_stop_button_clicked()
    {
      if (!m_WorkerThread)
      {
        std::cout << "Can't stop a worker thread. None is running." << std::endl;
      }
      else
      {
       // Order the worker thread to stop.
        m_Worker.stop_work();
        m_ButtonStop.set_sensitive(false);
      }
    }

    void ExampleWindow::update_start_stop_buttons()
    {
      const bool thread_is_running = m_WorkerThread != nullptr;

      m_ButtonStart.set_sensitive(!thread_is_running);
      m_ButtonStop.set_sensitive(thread_is_running);
    }

    void ExampleWindow::update_widgets()
    {
      double fraction_done;
      Glib::ustring message_from_worker_thread;
      m_Worker.get_data(&fraction_done, &message_from_worker_thread);

      m_ProgressBar.set_fraction(fraction_done);

      if (message_from_worker_thread != m_TextView.get_buffer()->get_text())
      {
        auto buffer = m_TextView.get_buffer();
        buffer->set_text(message_from_worker_thread);

        // Scroll the last inserted line into view. That's somewhat complicated.
        auto iter = buffer->end();
        iter.set_line_offset(0); // Beginning of last line
        auto mark = buffer->get_mark("last_line");
        buffer->move_mark(mark, iter);
        m_TextView.scroll_to(mark);
        // TextView::scroll_to(iter) is not perfect.
        // We do need a TextMark to always get the last line into view.
      }
    }

    void ExampleWindow::on_quit_button_clicked()
    {
      if (m_WorkerThread)
      {
        // Order the worker thread to stop and wait for it to stop.
        m_Worker.stop_work();
        if (m_WorkerThread->joinable())
          m_WorkerThread->join();
      }
      close();
    }

    // notify() is called from ExampleWorker::do_work(). It is executed in the worker
    // thread. It triggers a call to on_notification_from_worker_thread(), which is
    // executed in the GUI thread.
    void ExampleWindow::notify()
    {
      m_Dispatcher.emit();
    }

    void ExampleWindow::on_notification_from_worker_thread()
    {
      if (m_WorkerThread && m_Worker.has_stopped())
      {
        // Work is done.
        if (m_WorkerThread->joinable())
          m_WorkerThread->join();
        delete m_WorkerThread;
        m_WorkerThread = nullptr;
        update_start_stop_buttons();
      }
      update_widgets();
    }

File: `exampleworker.cc` (For use with gtkmm 4)

    #include "exampleworker.h"
    #include "examplewindow.h"
    #include <sstream>
    #include <chrono>

    ExampleWorker::ExampleWorker() :
      m_Mutex(),
      m_shall_stop(false),
      m_has_stopped(false),
      m_fraction_done(0.0),
      m_message()
    {
    }

    // Accesses to these data are synchronized by a mutex.
    // Some microseconds can be saved by getting all data at once, instead of having
    // separate get_fraction_done() and get_message() methods.
    void ExampleWorker::get_data(double* fraction_done, Glib::ustring* message) const
    {
      std::lock_guard<std::mutex> lock(m_Mutex);

      if (fraction_done)
        *fraction_done = m_fraction_done;

      if (message)
        *message = m_message;
    }

    void ExampleWorker::stop_work()
    {
      std::lock_guard<std::mutex> lock(m_Mutex);
      m_shall_stop = true;
    }

    bool ExampleWorker::has_stopped() const
    {
      std::lock_guard<std::mutex> lock(m_Mutex);
      return m_has_stopped;
    }

    void ExampleWorker::do_work(ExampleWindow* caller)
    {
      {
        std::lock_guard<std::mutex> lock(m_Mutex);
        m_has_stopped = false;
        m_fraction_done = 0.0;
        m_message = "";
      } // The mutex is unlocked here by lock's destructor.

      // Simulate a long calculation.
      for (int i = 0; ; ++i) // do until break
      {
        std::this_thread::sleep_for(std::chrono::milliseconds(250));

        {
          std::lock_guard<std::mutex> lock(m_Mutex);

          m_fraction_done += 0.01;

          if (i % 4 == 3)
          {
            std::ostringstream ostr;
            ostr << (m_fraction_done * 100.0) << "% done\n";
            m_message += ostr.str();
          }

          if (m_fraction_done >= 1.0)
          {
            m_message += "Finished";
            break;
          }
          if (m_shall_stop)
          {
            m_message += "Stopped";
            break;
          }
        }

        caller->notify();
      }

      {
        std::lock_guard<std::mutex> lock(m_Mutex);
        m_shall_stop = false;
        m_has_stopped = true;
      }

      caller->notify();
    }

File: `main.cc` (For use with gtkmm 4)

    #include "examplewindow.h"
    #include <gtkmm/application.h>

    int main(int argc, char* argv[])
    {
      auto app = Gtk::Application::create("org.gtkmm.example");

      //Shows the window and returns when it is closed.
      return app->make_window_and_run<ExampleWindow>(argc, argv);
    }

## Técnicas recomendadas

This section is simply a gathering of wisdom, general style guidelines and hints for creating gtkmm applications.

Use Meson! It is your friend :) It examines C and C++ files, determines how they depend on each other, and generates `build.ninja` or an equivalent file so the files can be compiled in the correct order. Meson permits automatic configuration of software installation, handling a large number of system quirks to increase portability.

Subclass Widgets to better organize your code. You should probably subclass your main Window at least. Then you can make your child Widgets and signal handlers members of that class.

Create your own signals instead of passing pointers around. Objects can communicate with each other via signals and signal handlers. This is much simpler than objects holding pointers to each other and calling each other's methods. gtkmm's classes use special versions of sigc::signal, but you should use normal sigc::signals, as described in the libsigc++ documentation.

### Tempo de vida da aplicação

Most applications will have only one Window, or only one main window. These applications can use Gtk::Application::make_window_and_run(int argc, char** argv, T_Args&&... args). It creates and shows a window. When the window is closed, make_window_and_run() deletes the window and returns to the caller. This might happen when the user closes the window, or when your code decides to close the window with Gtk::Window::close(). You can prevent the user from closing the window (for instance, if there are unsaved changes) by overriding Gtk::Window::on_close_request().

Most of our examples use this technique.

### Usando um widget gtkmm

Our examples all tend to have the same structure. They follow these steps for using a Widget:

1. Declare a variable of the type of Widget you wish to use, generally as member variable of a derived container class. You could also declare a pointer to the widget type, and then create it with `new` or `Gtk::make_managed()` in your code.

2. Set the attributes of the widget. If the widget has no default constructor, then you will need to initialize the widget in the initializer list of your container class's constructor.

3. Connect any signals you wish to use to the appropriate handlers.

4. Pack the widget into a container using the appropriate call, e.g. Gtk::Box::append().

If you don't want all widgets to be shown, call Gtk::Widget::set_visible(false) on the widgets that you don't want to show. If a container widget is hidden, all of its child widgets are also hidden, even if set_visible(false) is not called on the child widgets.

## Building applications

This chapter is similar to Building applications and following sections in the Getting Started chapter in the GTK documentation. The same application is built, but gtkmm is used instead of GTK.

An application consists of a number of files:

The binary file

  This gets installed in `/usr/bin`.

A desktop file

  The desktop file provides important information about the application to the desktop shell, such as its name, icon, D-Bus name, commandline to launch it, etc. It is installed in `/usr/share/applications`.

An icon

  The icon gets installed in `/usr/share/icons/hicolor/48x48/apps`, where it will be found regardless of the current theme.

A settings schema

  If the application uses Gio::Settings, it will install its schema in `/usr/share/glib-2.0/schemas`, so that tools like dconf-editor can find it.

Other resources

  Other files, such as Gtk::Builder ui files, are best loaded from resources stored in the application binary itself. This eliminates the need for most of the files that would traditionally be installed in an application-specific location in `/usr/share`.

gtkmm includes application support that is built on top of Gio::Application. In this chapter we'll build a simple application by starting from scratch, adding more and more pieces over time. Along the way, we'll learn about Gtk::Application, Gtk::Builder, resources, menus, settings, Gtk::HeaderBar, Gtk::Stack, Gtk::SearchBar, Gtk::ListBox, and more.

The full, buildable sources for these examples can be found in the `examples/book/buildapp` directory of the gtkmm-documentation source distribution, or online in the gtkmm-documentation git repository. You can build each example separately by using `meson` and `ninja` with the `meson.build` file or by using `make` with the `Makefile.example` file. For more information, see the `README` included in the `buildapp` directory.

### A trivial application

When using Gtk::Application, the `main()` function can be very simple. We just call Gtk::Application::run() on an instance of our application class.

All the application logic is in the application class, which is a subclass of Gtk::Application. Our example does not yet have any interesting functionality. All it does is open a window when it is activated without arguments, and open the files it is given, if it is started with arguments. (Or rather, our application class tries to open the files, but our subclassed application window does not yet do what it's told to do.)

To handle these two cases, we override signal_activate()'s default handler, which gets called when the application is launched without commandline arguments, and signal_open()'s default handler, which gets called when the application is launched with commandline arguments.

Gio::Application Reference

Gtk::Application Reference

Another important class that is part of the application support in gtkmm is Gtk::ApplicationWindow. It is typically subclassed as well. Our subclass does not do anything yet, so we will just get an empty window.

As part of the initial setup of our application, we also create an icon and a desktop file. Note that @bindir@ in the desktop file needs to be replaced with the actual path to the binary before this desktop file can be used.

Here is what we've achieved so far:

A trivial application

This does not look very impressive yet, but our application is already presenting itself on the session bus, it has single-instance semantics, and it accepts files as commandline arguments.

Source Code

File: `exampleapplication.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPLICATION_H
    #define GTKMM_EXAMPLEAPPLICATION_H

    #include <gtkmm.h>

    class ExampleAppWindow;

    class ExampleApplication: public Gtk::Application
    {
    protected:
      ExampleApplication();

    public:
      static Glib::RefPtr<ExampleApplication> create();

    protected:
      // Override default signal handlers:
      void on_activate() override;
      void on_open(const Gio::Application::type_vec_files& files,
        const Glib::ustring& hint) override;

    private:
      ExampleAppWindow* create_appwindow();
    };

    #endif /* GTKMM_EXAMPLEAPPLICATION_H */

File: `exampleappwindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPWINDOW_H_
    #define GTKMM_EXAMPLEAPPWINDOW_H_

    #include <gtkmm.h>

    class ExampleAppWindow : public Gtk::ApplicationWindow
    {
    public:
      ExampleAppWindow();

      void open_file_view(const Glib::RefPtr<Gio::File>& file);
    };

    #endif /* GTKMM_EXAMPLEAPPWINDOW_H */

File: `exampleapplication.cc` (For use with gtkmm 4)

    #include "exampleapplication.h"
    #include "exampleappwindow.h"

    ExampleApplication::ExampleApplication()
    : Gtk::Application("org.gtkmm.examples.application", Gio::Application::Flags::HANDLES_OPEN)
    {
      // Delete a window when it is removed from the application.
      signal_window_removed().connect([](Gtk::Window* window) { delete window; });
    }

    Glib::RefPtr<ExampleApplication> ExampleApplication::create()
    {
      return Glib::make_refptr_for_instance<ExampleApplication>(new ExampleApplication());
    }

    ExampleAppWindow* ExampleApplication::create_appwindow()
    {
      auto appwindow = new ExampleAppWindow();

      // Make sure that the application runs for as long this window is still open.
      add_window(*appwindow);

      // A window can be added to an application with Gtk::Application::add_window()
      // or Gtk::Window::set_application(). When all added windows have been removed,
      // the application stops running (Gtk::Application::run() returns),
      // unless Gio::Application::hold() has been called.

      return appwindow;
    }

    void ExampleApplication::on_activate()
    {
      // The application has been started, so let's show a window.
      auto appwindow = create_appwindow();
      appwindow->present();
    }

    void ExampleApplication::on_open(const Gio::Application::type_vec_files& files,
      const Glib::ustring& /* hint */)
    {
      // The application has been asked to open some files,
      // so let's open a new view for each one.
      ExampleAppWindow* appwindow = nullptr;
      auto windows = get_windows();
      if (windows.size() > 0)
        appwindow = dynamic_cast<ExampleAppWindow*>(windows[0]);

      if (!appwindow)
        appwindow = create_appwindow();

      for (const auto& file : files)
        appwindow->open_file_view(file);

      appwindow->present();
    }

File: `exampleappwindow.cc` (For use with gtkmm 4)

    #include "exampleappwindow.h"

    ExampleAppWindow::ExampleAppWindow()
    : Gtk::ApplicationWindow()
    {
    }

    void ExampleAppWindow::open_file_view(const Glib::RefPtr<Gio::File>& /* file */)
    {
    }

File: `main.cc` (For use with gtkmm 4)

    #include "exampleapplication.h"

    int main(int argc, char* argv[])
    {
      auto application = ExampleApplication::create();

      // Start the application, showing the initial window,
      // and opening extra views for any files that it is asked to open,
      // for instance as a command-line parameter.
      // run() will return when the last window has been closed.
      return application->run(argc, argv);
    }

File: `exampleapp.desktop.in` (For use with gtkmm 4)

    [Desktop Entry]
    Type=Application
    Name=Gtkmm example
    GenericName=Example
    Comment=From the "Programming with gtkmm 4" tutorial
    Icon=exampleapp
    StartupNotify=true
    Exec=@bindir@/exampleapp %U
    Categories=GNOME;GTK;Utility

### Populating the window

In this step, we use a Gtk::Builder instance to associate a Gtk::Builder ui file with our application window class.

Our simple ui file gives the window a title, and puts a Gtk::Stack widget as the main content.

To make use of this file in our application, we revisit our Gtk::ApplicationWindow subclass, and call Gtk::Builder::create_from_resource() and Gtk::Builder::get_widget_derived() from the ExampleAppWindow::create() method to get an instance of our subclassed Gtk::ApplicationWindow. See the Using derived widgets section for more information about get_widget_derived().

You may have noticed that we use the _from_resource() variant of the method that reads the ui file. Now we need to use GLib's resource functionality to include the ui file in the binary. This is commonly done by listing all resources in a .gresource.xml file. This file has to be converted into a C source file that will be compiled and linked into the application together with the other source files. To do so, we use the glib-compile-resources utility:

    $ glib-compile-resources --target=resources.c --generate-source exampleapp.gresource.xml

The Gio::Resource and glib-compile-resources section contains more information about resource files. If you build with Meson, use the `compile_resources()` function in Meson's GNOME module.

Our application now looks like this:

Populating the window

Source Code

File: `exampleapplication.h` (For use with gtkmm 4)

    #include "../step1/exampleapplication.h"
    // Equal to the corresponding file in step1

File: `exampleappwindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPWINDOW_H_
    #define GTKMM_EXAMPLEAPPWINDOW_H_

    #include <gtkmm.h>

    class ExampleAppWindow : public Gtk::ApplicationWindow
    {
    public:
      ExampleAppWindow(BaseObjectType* cobject,
        const Glib::RefPtr<Gtk::Builder>& refBuilder);

      static ExampleAppWindow* create();

      void open_file_view(const Glib::RefPtr<Gio::File>& file);

    protected:
      Glib::RefPtr<Gtk::Builder> m_refBuilder;
    };

    #endif /* GTKMM_EXAMPLEAPPWINDOW_H */

File: `exampleapplication.cc` (For use with gtkmm 4)

    #include "exampleapplication.h"
    #include "exampleappwindow.h"
    #include <iostream>
    #include <exception>

    ExampleApplication::ExampleApplication()
    : Gtk::Application("org.gtkmm.examples.application", Gio::Application::Flags::HANDLES_OPEN)
    {
      // Delete a window when it is removed from the application.
      signal_window_removed().connect([](Gtk::Window* window) { delete window; });
    }

    Glib::RefPtr<ExampleApplication> ExampleApplication::create()
    {
      return Glib::make_refptr_for_instance<ExampleApplication>(new ExampleApplication());
    }

    ExampleAppWindow* ExampleApplication::create_appwindow()
    {
      auto appwindow = ExampleAppWindow::create();

      // Make sure that the application runs for as long this window is still open.
      add_window(*appwindow);

      // A window can be added to an application with Gtk::Application::add_window()
      // or Gtk::Window::set_application(). When all added windows have been removed,
      // the application stops running (Gtk::Application::run() returns),
      // unless Gio::Application::hold() has been called.

      return appwindow;
    }

    void ExampleApplication::on_activate()
    {
      try
      {
        // The application has been started, so let's show a window.
        auto appwindow = create_appwindow();
        appwindow->present();
      }
      // If create_appwindow() throws an exception (perhaps from Gtk::Builder),
      // no window has been created, no window has been added to the application,
      // and therefore the application will stop running.
      catch (const Glib::Error& ex)
      {
        std::cerr << "ExampleApplication::on_activate(): " << ex.what() << std::endl;
      }
      catch (const std::exception& ex)
      {
        std::cerr << "ExampleApplication::on_activate(): " << ex.what() << std::endl;
      }
    }

    void ExampleApplication::on_open(const Gio::Application::type_vec_files& files,
      const Glib::ustring& /* hint */)
    {
      // The application has been asked to open some files,
      // so let's open a new view for each one.
      ExampleAppWindow* appwindow = nullptr;
      auto windows = get_windows();
      if (windows.size() > 0)
        appwindow = dynamic_cast<ExampleAppWindow*>(windows[0]);

      try
      {
        if (!appwindow)
          appwindow = create_appwindow();

        for (const auto& file : files)
          appwindow->open_file_view(file);

        appwindow->present();
      }
      catch (const Glib::Error& ex)
      {
        std::cerr << "ExampleApplication::on_open(): " << ex.what() << std::endl;
      }
      catch (const std::exception& ex)
      {
        std::cerr << "ExampleApplication::on_open(): " << ex.what() << std::endl;
      }
    }

File: `exampleappwindow.cc` (For use with gtkmm 4)

    #include "exampleappwindow.h"
    #include <stdexcept>

    ExampleAppWindow::ExampleAppWindow(BaseObjectType* cobject,
      const Glib::RefPtr<Gtk::Builder>& refBuilder)
    : Gtk::ApplicationWindow(cobject),
      m_refBuilder(refBuilder)
    {
    }

    //static
    ExampleAppWindow* ExampleAppWindow::create()
    {
      // Load the Builder file and instantiate its widgets.
      auto refBuilder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/window.ui");

      auto window = Gtk::Builder::get_widget_derived<ExampleAppWindow>(refBuilder, "app_window");
      if (!window)
        throw std::runtime_error("No \"app_window\" object in window.ui");

      return window;
    }

    void ExampleAppWindow::open_file_view(const Glib::RefPtr<Gio::File>& /* file */)
    {
    }

File: `main.cc` (For use with gtkmm 4)

    #include "../step1/main.cc"
    // Equal to the corresponding file in step1

File: `exampleapp.gresource.xml` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <gresources>
      <gresource prefix="/org/gtkmm/exampleapp">
        <file preprocess="xml-stripblanks">window.ui</file>
      </gresource>
    </gresources>

File: `window.ui` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <interface>
      <object class="GtkApplicationWindow" id="app_window">
        <property name="title" translatable="yes">Example Application</property>
        <property name="default-width">600</property>
        <property name="default-height">400</property>
        <child>
          <object class="GtkBox" id="content_box">
            <property name="orientation">vertical</property>
            <child>
              <object class="GtkStack" id="stack"/>
            </child>
          </object>
        </child>
      </object>
    </interface>

### Opening files

In this step, we make our application show the contents of all the files that it is given on the commandline.

To this end, we add a data member to our application window and keep a pointer to the Gtk::Stack there. We get the pointer with a call to Gtk::Builder::get_widget() in the application window's constructor.

Now we revisit the ExampleAppWindow::open_file_view() method that is called for each commandline argument, and construct a Gtk::TextView that we then add as a page to the stack.

Lastly, we add a Gtk::StackSwitcher to the titlebar area in the ui file, and we tell it to display information about our stack.

The stack switcher gets all its information it needs to display tabs from the stack that it belongs to. Here, we are passing the label to show for each file as the last argument to the Gtk::Stack::add() method.

Our application is beginning to take shape:

Opening files

Source Code

File: `exampleapplication.h` (For use with gtkmm 4)

    #include "../step1/exampleapplication.h"
    // Equal to the corresponding file in step1

File: `exampleappwindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPWINDOW_H_
    #define GTKMM_EXAMPLEAPPWINDOW_H_

    #include <gtkmm.h>

    class ExampleAppWindow : public Gtk::ApplicationWindow
    {
    public:
      ExampleAppWindow(BaseObjectType* cobject,
        const Glib::RefPtr<Gtk::Builder>& refBuilder);

      static ExampleAppWindow* create();

      void open_file_view(const Glib::RefPtr<Gio::File>& file);

    protected:
      Glib::RefPtr<Gtk::Builder> m_refBuilder;
      Gtk::Stack* m_stack {nullptr};
    };

    #endif /* GTKMM_EXAMPLEAPPWINDOW_H */

File: `exampleapplication.cc` (For use with gtkmm 4)

    #include "../step2/exampleapplication.cc"
    // Equal to the corresponding file in step2

File: `exampleappwindow.cc` (For use with gtkmm 4)

    #include "exampleappwindow.h"
    #include <iostream>
    #include <stdexcept>

    ExampleAppWindow::ExampleAppWindow(BaseObjectType* cobject,
      const Glib::RefPtr<Gtk::Builder>& refBuilder)
    : Gtk::ApplicationWindow(cobject),
      m_refBuilder(refBuilder)
    {
      m_stack = m_refBuilder->get_widget<Gtk::Stack>("stack");
      if (!m_stack)
        throw std::runtime_error("No \"stack\" object in window.ui");
    }

    //static
    ExampleAppWindow* ExampleAppWindow::create()
    {
      // Load the Builder file and instantiate its widgets.
      auto refBuilder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/window.ui");

      auto window = Gtk::Builder::get_widget_derived<ExampleAppWindow>(refBuilder, "app_window");
      if (!window)
        throw std::runtime_error("No \"app_window\" object in window.ui");

      return window;
    }

    void ExampleAppWindow::open_file_view(const Glib::RefPtr<Gio::File>& file)
    {
      const Glib::ustring basename = file->get_basename();

      auto scrolled = Gtk::make_managed<Gtk::ScrolledWindow>();
      scrolled->set_expand(true);
      auto view = Gtk::make_managed<Gtk::TextView>();
      view->set_editable(false);
      view->set_cursor_visible(false);
      scrolled->set_child(*view);
      m_stack->add(*scrolled, basename, basename);

      try
      {
        char* contents = nullptr;
        gsize length = 0;

        file->load_contents(contents, length);
        view->get_buffer()->set_text(contents, contents+length);
        g_free(contents);
      }
      catch (const Glib::Error& ex)
      {
        std::cout << "ExampleAppWindow::open_file_view(\"" << file->get_parse_name()
          << "\"):\n  " << ex.what() << std::endl;
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "../step1/main.cc"
    // Equal to the corresponding file in step1

File: `window.ui` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <interface>
      <object class="GtkApplicationWindow" id="app_window">
        <property name="title" translatable="yes">Example Application</property>
        <property name="default-width">600</property>
        <property name="default-height">400</property>
        <child type="titlebar">
          <object class="GtkHeaderBar" id="header">
            <child type="title">
              <object class="GtkStackSwitcher" id="tabs">
                <property name="stack">stack</property>
              </object>
            </child>
          </object>
        </child>
        <child>
          <object class="GtkBox" id="content_box">
            <property name="orientation">vertical</property>
            <child>
              <object class="GtkStack" id="stack"/>
            </child>
          </object>
        </child>
      </object>
    </interface>

### A menu

The menu is shown at the right side of the headerbar. It is meant to collect infrequently used actions that affect the whole application.

Just like the application window, we specify our menu in a ui file, and add it as a resource to our binary.

To make the menu appear, we have to load the ui file and associate the resulting menu model with the menu button that we've added to the headerbar. Since menus work by activating Gio::Actions, we also have to add a suitable set of actions to our application.

Adding the actions is best done in the on_startup() default signal handler, which is guaranteed to be called once for each primary application instance.

Our preferences menu item does not do anything yet, but the Quit menu item is fully functional. It can also be activated by the usual Ctrl-Q shortcut. The shortcut is added with Gtk::Application::set_accel_for_action().

The menu looks like this:

A menu

Source Code

File: `exampleapplication.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPLICATION_H
    #define GTKMM_EXAMPLEAPPLICATION_H

    #include <gtkmm.h>

    class ExampleAppWindow;

    class ExampleApplication: public Gtk::Application
    {
    protected:
      ExampleApplication();

    public:
      static Glib::RefPtr<ExampleApplication> create();

    protected:
      // Override default signal handlers:
      void on_startup() override;
      void on_activate() override;
      void on_open(const Gio::Application::type_vec_files& files,
        const Glib::ustring& hint) override;

    private:
      ExampleAppWindow* create_appwindow();
      void on_action_preferences();
      void on_action_quit();
    };

    #endif /* GTKMM_EXAMPLEAPPLICATION_H */

File: `exampleappwindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPWINDOW_H_
    #define GTKMM_EXAMPLEAPPWINDOW_H_

    #include <gtkmm.h>

    class ExampleAppWindow : public Gtk::ApplicationWindow
    {
    public:
      ExampleAppWindow(BaseObjectType* cobject,
        const Glib::RefPtr<Gtk::Builder>& refBuilder);

      static ExampleAppWindow* create();

      void open_file_view(const Glib::RefPtr<Gio::File>& file);

    protected:
      Glib::RefPtr<Gtk::Builder> m_refBuilder;
      Gtk::Stack* m_stack {nullptr};
      Gtk::MenuButton* m_gears {nullptr};
    };

    #endif /* GTKMM_EXAMPLEAPPWINDOW_H */

File: `exampleapplication.cc` (For use with gtkmm 4)

    #include "exampleapplication.h"
    #include "exampleappwindow.h"
    #include <iostream>
    #include <exception>

    ExampleApplication::ExampleApplication()
    : Gtk::Application("org.gtkmm.examples.application", Gio::Application::Flags::HANDLES_OPEN)
    {
      // Delete a window when it is removed from the application.
      signal_window_removed().connect([](Gtk::Window* window) { delete window; });
    }

    Glib::RefPtr<ExampleApplication> ExampleApplication::create()
    {
      return Glib::make_refptr_for_instance<ExampleApplication>(new ExampleApplication());
    }

    ExampleAppWindow* ExampleApplication::create_appwindow()
    {
      auto appwindow = ExampleAppWindow::create();

      // Make sure that the application runs for as long this window is still open.
      add_window(*appwindow);

      // A window can be added to an application with Gtk::Application::add_window()
      // or Gtk::Window::set_application(). When all added windows have been removed,
      // the application stops running (Gtk::Application::run() returns),
      // unless Gio::Application::hold() has been called.

      return appwindow;
    }

    void ExampleApplication::on_startup()
    {
      // Call the base class's implementation.
      Gtk::Application::on_startup();

      // Add actions and keyboard accelerators for the menu.
      add_action("preferences", sigc::mem_fun(*this, &ExampleApplication::on_action_preferences));
      add_action("quit", sigc::mem_fun(*this, &ExampleApplication::on_action_quit));
      set_accel_for_action("app.quit", "<Ctrl>Q");
    }

    void ExampleApplication::on_activate()
    {
      try
      {
        // The application has been started, so let's show a window.
        auto appwindow = create_appwindow();
        appwindow->present();
      }
      // If create_appwindow() throws an exception (perhaps from Gtk::Builder),
      // no window has been created, no window has been added to the application,
      // and therefore the application will stop running.
      catch (const Glib::Error& ex)
      {
        std::cerr << "ExampleApplication::on_activate(): " << ex.what() << std::endl;
      }
      catch (const std::exception& ex)
      {
        std::cerr << "ExampleApplication::on_activate(): " << ex.what() << std::endl;
      }
    }

    void ExampleApplication::on_open(const Gio::Application::type_vec_files& files,
      const Glib::ustring& /* hint */)
    {
      // The application has been asked to open some files,
      // so let's open a new view for each one.
      ExampleAppWindow* appwindow = nullptr;
      auto windows = get_windows();
      if (windows.size() > 0)
        appwindow = dynamic_cast<ExampleAppWindow*>(windows[0]);

      try
      {
        if (!appwindow)
          appwindow = create_appwindow();

        for (const auto& file : files)
          appwindow->open_file_view(file);

        appwindow->present();
      }
      catch (const Glib::Error& ex)
      {
        std::cerr << "ExampleApplication::on_open(): " << ex.what() << std::endl;
      }
      catch (const std::exception& ex)
      {
        std::cerr << "ExampleApplication::on_open(): " << ex.what() << std::endl;
      }
    }

    void ExampleApplication::on_action_preferences()
    {

    }

    void ExampleApplication::on_action_quit()
    {
      // Gio::Application::quit() will make Gio::Application::run() return,
      // but it's a crude way of ending the program. The window is not removed
      // from the application. Neither the window's nor the application's
      // destructors will be called, because there will be remaining reference
      // counts in both of them. If we want the destructors to be called, we
      // must remove the window from the application. See ExampleApplication's constructor.
      // A window can be removed from an application with Gtk::Application::remove_window()
      // or Gtk::Window::unset_application().
      auto windows = get_windows();
      for (auto window : windows)
        remove_window(*window);

      // Not really necessary, when Gtk::Application::remove_window() is called,
      // unless Gio::Application::hold() has been called without a corresponding
      // call to Gio::Application::release().
      quit();
    }

File: `exampleappwindow.cc` (For use with gtkmm 4)

    #include "exampleappwindow.h"
    #include <iostream>
    #include <stdexcept>

    ExampleAppWindow::ExampleAppWindow(BaseObjectType* cobject,
      const Glib::RefPtr<Gtk::Builder>& refBuilder)
    : Gtk::ApplicationWindow(cobject),
      m_refBuilder(refBuilder)
    {
      // Get widgets from the Gtk::Builder file.
      m_stack = m_refBuilder->get_widget<Gtk::Stack>("stack");
      if (!m_stack)
        throw std::runtime_error("No \"stack\" object in window.ui");

      m_gears = m_refBuilder->get_widget<Gtk::MenuButton>("gears");
      if (!m_gears)
        throw std::runtime_error("No \"gears\" object in window.ui");

      // Connect the menu to the MenuButton m_gears.
      // (The connection between action and menu item is specified in gears_menu.ui.)
      auto menu_builder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/gears_menu.ui");
      auto menu = menu_builder->get_object<Gio::MenuModel>("menu");
      if (!menu)
        throw std::runtime_error("No \"menu\" object in gears_menu.ui");

      m_gears->set_menu_model(menu);
    }

    //static
    ExampleAppWindow* ExampleAppWindow::create()
    {
      // Load the Builder file and instantiate its widgets.
      auto refBuilder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/window.ui");

      auto window = Gtk::Builder::get_widget_derived<ExampleAppWindow>(refBuilder, "app_window");
      if (!window)
        throw std::runtime_error("No \"app_window\" object in window.ui");

      return window;
    }

    void ExampleAppWindow::open_file_view(const Glib::RefPtr<Gio::File>& file)
    {
      const Glib::ustring basename = file->get_basename();

      auto scrolled = Gtk::make_managed<Gtk::ScrolledWindow>();
      scrolled->set_expand(true);
      auto view = Gtk::make_managed<Gtk::TextView>();
      view->set_editable(false);
      view->set_cursor_visible(false);
      scrolled->set_child(*view);
      m_stack->add(*scrolled, basename, basename);

      try
      {
        char* contents = nullptr;
        gsize length = 0;

        file->load_contents(contents, length);
        view->get_buffer()->set_text(contents, contents+length);
        g_free(contents);
      }
      catch (const Glib::Error& ex)
      {
        std::cout << "ExampleAppWindow::open_file_view(\"" << file->get_parse_name()
          << "\"):\n  " << ex.what() << std::endl;
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "../step1/main.cc"
    // Equal to the corresponding file in step1

File: `exampleapp.gresource.xml` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <gresources>
      <gresource prefix="/org/gtkmm/exampleapp">
        <file preprocess="xml-stripblanks">window.ui</file>
        <file preprocess="xml-stripblanks">gears_menu.ui</file>
      </gresource>
    </gresources>

File: `gears_menu.ui` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <interface>
      <menu id="menu">
        <section>
          <item>
            <attribute name="label" translatable="yes">_Preferences</attribute>
            <attribute name="action">app.preferences</attribute>
          </item>
        </section>
        <section>
          <item>
            <attribute name="label" translatable="yes">_Quit</attribute>
            <attribute name="action">app.quit</attribute>
          </item>
        </section>
      </menu>
    </interface>

File: `window.ui` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <interface>
      <object class="GtkApplicationWindow" id="app_window">
        <property name="title" translatable="yes">Example Application</property>
        <property name="default-width">600</property>
        <property name="default-height">400</property>
        <child type="titlebar">
          <object class="GtkHeaderBar" id="header">
            <child type="title">
              <object class="GtkStackSwitcher" id="tabs">
                <property name="stack">stack</property>
              </object>
            </child>
            <child type="end">
              <object class="GtkMenuButton" id="gears">
                <property name="direction">none</property>
              </object>
            </child>
          </object>
        </child>
        <child>
          <object class="GtkBox" id="content_box">
            <property name="orientation">vertical</property>
            <child>
              <object class="GtkStack" id="stack"/>
            </child>
          </object>
        </child>
      </object>
    </interface>

### A preference dialog

A typical application will have some preferences that should be remembered from one run to the next. Even for our simple example application, we may want to change the font that is used for the content.

We are going to use Gio::Settings to store our preferences. Gio::Settings requires a schema that describes our settings, in our case the `org.gtkmm.exampleapp.gschema.xml` file.

Before we can make use of this schema in our application, we need to compile it into the binary form that Gio::Settings expects. GIO provides macros to do this in autotools-based projects. See the description of GSettings. Meson provides the `compile_schemas()` function in the GNOME module.

Next, we need to connect our settings to the widgets that they are supposed to control. One convenient way to do this is to use Gio::Settings::bind() to bind settings keys to object properties, as we do for the transition setting in ExampleAppWindow's constructor.

    m_settings = Gio::Settings::create("org.gtkmm.exampleapp");
    m_settings->bind("transition", m_stack->property_transition_type());

The code to connect the font setting is a little more involved, since it corresponds to an object property in a Gtk::TextTag that we must first create. The code is in ExampleAppWindow::open_file_view().

    auto tag = buffer->create_tag();
    m_settings->bind("font", tag->property_font());
    buffer->apply_tag(tag, buffer->begin(), buffer->end());

At this point, the application will already react if you change one of the settings, e.g. using the `gsettings` commandline tool. Of course, we expect the application to provide a preference dialog for these. So lets do that now. Our preference dialog will be a subclass of Gtk::Window, and we'll use the same techniques that we've already seen in ExampleAppWindow: a Gtk::Builder ui file and settings bindings. In this case the bindings are more involved, though. We use Gtk::FontDialogButton and Gtk::DropDown in the preference dialog. The types of the properties in these classes can't be automatically converted to the string type that Gio::Settings requires.

When we've created the `prefs.ui` file and the ExampleAppPrefs class, we revisit the ExampleApplication::on_action_preferences() method in our application class, and make it open a new preference dialog.

    auto prefs_dialog = ExampleAppPrefs::create(*get_active_window());
    prefs_dialog->present();

After all this work, our application can now show a preference dialog like this:

A preference dialog

Source Code

File: `exampleapplication.h` (For use with gtkmm 4)

    #include "../step4/exampleapplication.h"
    // Equal to the corresponding file in step4

File: `exampleappprefs.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPPREFS_H_
    #define GTKMM_EXAMPLEAPPPREFS_H_

    #include <gtkmm.h>

    #ifdef GLIBMM_CHECK_VERSION
    #define HAS_GIO_SETTINGS_BIND_WITH_MAPPING GLIBMM_CHECK_VERSION(2,75,0)
    #else
    #define HAS_GIO_SETTINGS_BIND_WITH_MAPPING 0
    #endif

    class ExampleAppPrefs : public Gtk::Window
    {
    public:
      ExampleAppPrefs(BaseObjectType* cobject,
        const Glib::RefPtr<Gtk::Builder>& refBuilder);

      static ExampleAppPrefs* create(Gtk::Window& parent);

    protected:
    #if HAS_GIO_SETTINGS_BIND_WITH_MAPPING
      // Mappings from Gio::Settings to properties
      static std::optional<unsigned int> map_from_ustring_to_int(const Glib::ustring& transition);
      static std::optional<Glib::ustring> map_from_int_to_ustring(const unsigned int& pos);
    #else
      // Signal handlers
      void on_font_setting_changed(const Glib::ustring& key);
      void on_font_selection_changed();
      void on_transition_setting_changed(const Glib::ustring& key);
      void on_transition_selection_changed();
    #endif
      Glib::RefPtr<Gtk::Builder> m_refBuilder;
      Glib::RefPtr<Gio::Settings> m_settings;
      Gtk::FontDialogButton* m_font {nullptr};
      Gtk::DropDown* m_transition {nullptr};
    };

    #endif /* GTKMM_EXAMPLEAPPPREFS_H_ */

File: `exampleappwindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPWINDOW_H_
    #define GTKMM_EXAMPLEAPPWINDOW_H_

    #include <gtkmm.h>

    class ExampleAppWindow : public Gtk::ApplicationWindow
    {
    public:
      ExampleAppWindow(BaseObjectType* cobject,
        const Glib::RefPtr<Gtk::Builder>& refBuilder);

      static ExampleAppWindow* create();

      void open_file_view(const Glib::RefPtr<Gio::File>& file);

    protected:
      Glib::RefPtr<Gtk::Builder> m_refBuilder;
      Glib::RefPtr<Gio::Settings> m_settings;
      Gtk::Stack* m_stack {nullptr};
      Gtk::MenuButton* m_gears {nullptr};
    };

    #endif /* GTKMM_EXAMPLEAPPWINDOW_H */

File: `exampleapplication.cc` (For use with gtkmm 4)

    #include "exampleapplication.h"
    #include "exampleappwindow.h"
    #include "exampleappprefs.h"
    #include <iostream>
    #include <exception>

    ExampleApplication::ExampleApplication()
    : Gtk::Application("org.gtkmm.examples.application", Gio::Application::Flags::HANDLES_OPEN)
    {
      // Delete a window when it is removed from the application.
      signal_window_removed().connect([](Gtk::Window* window) { delete window; });
    }

    Glib::RefPtr<ExampleApplication> ExampleApplication::create()
    {
      return Glib::make_refptr_for_instance<ExampleApplication>(new ExampleApplication());
    }

    ExampleAppWindow* ExampleApplication::create_appwindow()
    {
      auto appwindow = ExampleAppWindow::create();

      // Make sure that the application runs for as long this window is still open.
      add_window(*appwindow);

      // A window can be added to an application with Gtk::Application::add_window()
      // or Gtk::Window::set_application(). When all added windows have been removed,
      // the application stops running (Gtk::Application::run() returns),
      // unless Gio::Application::hold() has been called.

      return appwindow;
    }

    void ExampleApplication::on_startup()
    {
      // Call the base class's implementation.
      Gtk::Application::on_startup();

      // Add actions and keyboard accelerators for the menu.
      add_action("preferences", sigc::mem_fun(*this, &ExampleApplication::on_action_preferences));
      add_action("quit", sigc::mem_fun(*this, &ExampleApplication::on_action_quit));
      set_accel_for_action("app.quit", "<Ctrl>Q");
    }

    void ExampleApplication::on_activate()
    {
      try
      {
        // The application has been started, so let's show a window.
        auto appwindow = create_appwindow();
        appwindow->present();
      }
      // If create_appwindow() throws an exception (perhaps from Gtk::Builder),
      // no window has been created, no window has been added to the application,
      // and therefore the application will stop running.
      catch (const Glib::Error& ex)
      {
        std::cerr << "ExampleApplication::on_activate(): " << ex.what() << std::endl;
      }
      catch (const std::exception& ex)
      {
        std::cerr << "ExampleApplication::on_activate(): " << ex.what() << std::endl;
      }
    }

    void ExampleApplication::on_open(const Gio::Application::type_vec_files& files,
      const Glib::ustring& /* hint */)
    {
      // The application has been asked to open some files,
      // so let's open a new view for each one.
      ExampleAppWindow* appwindow = nullptr;
      auto windows = get_windows();
      if (windows.size() > 0)
        appwindow = dynamic_cast<ExampleAppWindow*>(windows[0]);

      try
      {
        if (!appwindow)
          appwindow = create_appwindow();

        for (const auto& file : files)
          appwindow->open_file_view(file);

        appwindow->present();
      }
      catch (const Glib::Error& ex)
      {
        std::cerr << "ExampleApplication::on_open(): " << ex.what() << std::endl;
      }
      catch (const std::exception& ex)
      {
        std::cerr << "ExampleApplication::on_open(): " << ex.what() << std::endl;
      }
    }

    void ExampleApplication::on_action_preferences()
    {
      try
      {
        auto prefs_dialog = ExampleAppPrefs::create(*get_active_window());
        prefs_dialog->present();

        // Delete the dialog when it is hidden.
        prefs_dialog->signal_hide().connect([prefs_dialog](){ delete prefs_dialog; });
      }
      catch (const Glib::Error& ex)
      {
        std::cerr << "ExampleApplication::on_action_preferences(): " << ex.what() << std::endl;
      }
      catch (const std::exception& ex)
      {
        std::cerr << "ExampleApplication::on_action_preferences(): " << ex.what() << std::endl;
      }
    }

    void ExampleApplication::on_action_quit()
    {
      // Gio::Application::quit() will make Gio::Application::run() return,
      // but it's a crude way of ending the program. The window is not removed
      // from the application. Neither the window's nor the application's
      // destructors will be called, because there will be remaining reference
      // counts in both of them. If we want the destructors to be called, we
      // must remove the window from the application. See ExampleApplication's constructor.
      // A window can be removed from an application with Gtk::Application::remove_window()
      // or Gtk::Window::unset_application().
      auto windows = get_windows();
      for (auto window : windows)
        remove_window(*window);

      // Not really necessary, when Gtk::Application::remove_window() is called,
      // unless Gio::Application::hold() has been called without a corresponding
      // call to Gio::Application::release().
      quit();
    }

File: `exampleappprefs.cc` (For use with gtkmm 4)

    #include "exampleappprefs.h"
    #include "exampleappwindow.h"
    #include <array>
    #include <stdexcept>

    namespace
    {
    struct TransitionTypeStruct
    {
      Glib::ustring id;   // Value of "transition" key in Gio::Settings
      Glib::ustring text; // Text in the DropDown list
    };

    const std::array<TransitionTypeStruct, 3> transitionTypes =
    {
      TransitionTypeStruct{"none",             "None"},
      TransitionTypeStruct{"crossfade",        "Fade"},
      TransitionTypeStruct{"slide-left-right", "Slide"}
    };

    } // anonymous namespace

    ExampleAppPrefs::ExampleAppPrefs(BaseObjectType* cobject,
      const Glib::RefPtr<Gtk::Builder>& refBuilder)
    : Gtk::Window(cobject),
      m_refBuilder(refBuilder)
    {
      m_font = m_refBuilder->get_widget<Gtk::FontDialogButton>("font");
      if (!m_font)
        throw std::runtime_error("No \"font\" object in prefs.ui");

      m_transition = m_refBuilder->get_widget<Gtk::DropDown>("transition");
      if (!m_transition)
        throw std::runtime_error("No \"transition\" object in prefs.ui");

      // DropDown for transition type.
      auto string_list = Gtk::StringList::create();
      for (const auto& transitionType : transitionTypes)
        string_list->append(transitionType.text);

      m_transition->set_model(string_list);

      m_settings = Gio::Settings::create("org.gtkmm.exampleapp");

      // Connect preference properties to the Gio::Settings.
    #if HAS_GIO_SETTINGS_BIND_WITH_MAPPING
      m_settings->bind<Glib::ustring, Pango::FontDescription>("font",
        m_font->property_font_desc(), Gio::Settings::BindFlags::DEFAULT,
        [](const auto& font) { return Pango::FontDescription(font); },
        [](const auto& fontdesc) { return fontdesc.to_string(); }
      );
      m_settings->bind<Glib::ustring, unsigned int>("transition",
        m_transition->property_selected(), Gio::Settings::BindFlags::DEFAULT,
        [](const auto& transition) { return map_from_ustring_to_int(transition); },
        [](const auto& pos) { return map_from_int_to_ustring(pos); }
      );
    #else
      // This is easier when g_settings_bind_with_mapping() is
      // wrapped in a Gio::Settings method.
      m_settings->signal_changed("font").connect(
        sigc::mem_fun(*this, &ExampleAppPrefs::on_font_setting_changed));
      m_font->property_font_desc().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleAppPrefs::on_font_selection_changed));

      m_settings->signal_changed("transition").connect(
        sigc::mem_fun(*this, &ExampleAppPrefs::on_transition_setting_changed));
      m_transition->property_selected().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleAppPrefs::on_transition_selection_changed));

      // Synchronize the preferences dialog with m_settings.
      on_font_setting_changed("font");
      on_transition_setting_changed("transition");
    #endif
    }

    //static
    ExampleAppPrefs* ExampleAppPrefs::create(Gtk::Window& parent)
    {
      // Load the Builder file and instantiate its widgets.
      auto refBuilder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/prefs.ui");

      auto dialog = Gtk::Builder::get_widget_derived<ExampleAppPrefs>(refBuilder, "prefs_dialog");
      if (!dialog)
        throw std::runtime_error("No \"prefs_dialog\" object in prefs.ui");

      dialog->set_transient_for(parent);

      return dialog;
    }

    #if HAS_GIO_SETTINGS_BIND_WITH_MAPPING
    std::optional<unsigned int> ExampleAppPrefs::map_from_ustring_to_int(const Glib::ustring& transition)
    {
      for (std::size_t i = 0; i < transitionTypes.size(); ++i)
      {
        if (transitionTypes[i].id == transition)
          return i;
      }
      return std::nullopt;
    }

    std::optional<Glib::ustring> ExampleAppPrefs::map_from_int_to_ustring(const unsigned int& pos)
    {
      if (pos >= transitionTypes.size())
        return std::nullopt;
      return transitionTypes[pos].id;
    }
    #else
    void ExampleAppPrefs::on_font_setting_changed(const Glib::ustring& /* key */)
    {
      const auto font_setting = m_settings->get_string("font");
      const auto font_button = m_font->get_font_desc().to_string();
      if (font_setting != font_button)
        m_font->set_font_desc(Pango::FontDescription(font_setting));
    }

    void ExampleAppPrefs::on_font_selection_changed()
    {
      const auto font_setting = m_settings->get_string("font");
      const auto font_button = m_font->get_font_desc().to_string();
      if (font_setting != font_button)
        m_settings->set_string("font", font_button);
    }

    void ExampleAppPrefs::on_transition_setting_changed(const Glib::ustring& /* key */)
    {
      const auto transition_setting = m_settings->get_string("transition");
      const auto transition_button = transitionTypes[m_transition->get_selected()].id;
      if (transition_setting != transition_button)
      {
        for (std::size_t i = 0; i < transitionTypes.size(); ++i)
        {
          if (transitionTypes[i].id == transition_setting)
          {
            m_transition->set_selected(i);
            break;
          }
        }
      }
    }

    void ExampleAppPrefs::on_transition_selection_changed()
    {
      const auto pos = m_transition->get_selected();
      if (pos >= transitionTypes.size())
        return;
      const auto transition_setting = m_settings->get_string("transition");
      const auto transition_button = transitionTypes[pos].id;
      if (transition_setting != transition_button)
        m_settings->set_string("transition", transition_button);
    }
    #endif

File: `exampleappwindow.cc` (For use with gtkmm 4)

    #include "exampleappwindow.h"
    #include <iostream>
    #include <stdexcept>

    ExampleAppWindow::ExampleAppWindow(BaseObjectType* cobject,
      const Glib::RefPtr<Gtk::Builder>& refBuilder)
    : Gtk::ApplicationWindow(cobject),
      m_refBuilder(refBuilder)
    {
      // Get widgets from the Gtk::Builder file.
      m_stack = m_refBuilder->get_widget<Gtk::Stack>("stack");
      if (!m_stack)
        throw std::runtime_error("No \"stack\" object in window.ui");

      m_gears = m_refBuilder->get_widget<Gtk::MenuButton>("gears");
      if (!m_gears)
        throw std::runtime_error("No \"gears\" object in window.ui");

      // Bind settings.
      m_settings = Gio::Settings::create("org.gtkmm.exampleapp");
      m_settings->bind("transition", m_stack->property_transition_type());

      // Connect the menu to the MenuButton m_gears.
      // (The connection between action and menu item is specified in gears_menu.ui.)
      auto menu_builder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/gears_menu.ui");
      auto menu = menu_builder->get_object<Gio::MenuModel>("menu");
      if (!menu)
        throw std::runtime_error("No \"menu\" object in gears_menu.ui");

      m_gears->set_menu_model(menu);
    }

    //static
    ExampleAppWindow* ExampleAppWindow::create()
    {
      // Load the Builder file and instantiate its widgets.
      auto refBuilder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/window.ui");

      auto window = Gtk::Builder::get_widget_derived<ExampleAppWindow>(refBuilder, "app_window");
      if (!window)
        throw std::runtime_error("No \"app_window\" object in window.ui");

      return window;
    }

    void ExampleAppWindow::open_file_view(const Glib::RefPtr<Gio::File>& file)
    {
      const Glib::ustring basename = file->get_basename();

      auto scrolled = Gtk::make_managed<Gtk::ScrolledWindow>();
      scrolled->set_expand(true);
      auto view = Gtk::make_managed<Gtk::TextView>();
      view->set_editable(false);
      view->set_cursor_visible(false);
      scrolled->set_child(*view);
      m_stack->add(*scrolled, basename, basename);

      auto buffer = view->get_buffer();
      try
      {
        char* contents = nullptr;
        gsize length = 0;

        file->load_contents(contents, length);
        buffer->set_text(contents, contents+length);
        g_free(contents);
      }
      catch (const Glib::Error& ex)
      {
        std::cout << "ExampleAppWindow::open_file_view(\"" << file->get_parse_name()
          << "\"):\n  " << ex.what() << std::endl;
      }

      auto tag = buffer->create_tag();
      m_settings->bind("font", tag->property_font());
      buffer->apply_tag(tag, buffer->begin(), buffer->end());
    }

File: `main.cc` (For use with gtkmm 4)

    #include "exampleapplication.h"

    int main(int argc, char* argv[])
    {
      // Since this example is running uninstalled, we have to help it find its
      // schema. This is *not* necessary in a properly installed application.
      Glib::setenv ("GSETTINGS_SCHEMA_DIR", ".", false);

      auto application = ExampleApplication::create();

      // Start the application, showing the initial window,
      // and opening extra views for any files that it is asked to open,
      // for instance as a command-line parameter.
      // run() will return when the last window has been closed.
      return application->run(argc, argv);
    }

File: `exampleapp.gresource.xml` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <gresources>
      <gresource prefix="/org/gtkmm/exampleapp">
        <file preprocess="xml-stripblanks">window.ui</file>
        <file preprocess="xml-stripblanks">gears_menu.ui</file>
        <file preprocess="xml-stripblanks">prefs.ui</file>
      </gresource>
    </gresources>

File: `prefs.ui` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <interface>
      <object class="GtkWindow" id="prefs_dialog">
        <property name="title" translatable="yes">Preferences</property>
        <property name="resizable">False</property>
        <property name="modal">True</property>
        <property name="hide_on_close">True</property>
        <child>
          <object class="GtkGrid" id="grid">
            <property name="margin-start">12</property>
            <property name="margin-end">12</property>
            <property name="margin-top">12</property>
            <property name="margin-bottom">12</property>
            <property name="row-spacing">12</property>
            <property name="column-spacing">12</property>
            <child>
              <object class="GtkLabel" id="fontlabel">
                <property name="label">_Font:</property>
                <property name="use-underline">True</property>
                <property name="mnemonic-widget">font</property>
                <property name="xalign">1</property>
                <layout>
                  <property name="column">0</property>
                  <property name="row">0</property>
                </layout>
              </object>
            </child>
            <child>
              <object class="GtkFontDialogButton" id="font">
                <property name="dialog">
                  <object class="GtkFontDialog"/>
                </property>
                <layout>
                  <property name="column">1</property>
                  <property name="row">0</property>
                </layout>
              </object>
            </child>
            <child>
              <object class="GtkLabel" id="transitionlabel">
                <property name="label">_Transition:</property>
                <property name="use-underline">True</property>
                <property name="mnemonic-widget">transition</property>
                <property name="xalign">1</property>
                <layout>
                  <property name="column">0</property>
                  <property name="row">1</property>
                </layout>
              </object>
            </child>
            <child>
              <object class="GtkDropDown" id="transition">
                <layout>
                  <property name="column">1</property>
                  <property name="row">1</property>
                </layout>
              </object>
            </child>
          </object>
        </child>
      </object>
    </interface>

File: `org.gtkmm.exampleapp.gschema.xml` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <schemalist>
      <schema path="/org/gtkmm/exampleapp/" id="org.gtkmm.exampleapp">
        <key name="font" type="s">
          <default>'Monospace 12'</default>
          <summary>Font</summary>
          <description>The font to be used for content.</description>
        </key>
        <key name="transition" type="s">
          <choices>
            <choice value='none'/>
            <choice value='crossfade'/>
            <choice value='slide-left-right'/>
          </choices>
          <default>'none'</default>
          <summary>Transition</summary>
          <description>The transition to use when switching tabs.</description>
        </key>
      </schema>
    </schemalist>

### Adding a search bar

We continue to flesh out the functionality of our application. For now, we add search. gtkmm supports this with Gtk::SearchEntry and Gtk::SearchBar. The search bar is a widget that can slide in from the top to present a search entry.

We add a toggle button to the header bar, which can be used to slide out the search bar below the header bar. The new widgets are added in the `window.ui` file.

Implementing the search needs quite a few code changes that we are not going to completely go over here. The central piece of the search implementation is a signal handler that listens for text changes in the search entry, shown here without error handling.

    void ExampleAppWindow::on_search_text_changed()
    {
      const auto text = m_searchentry->get_text();
      auto tab = dynamic_cast<Gtk::ScrolledWindow*>(m_stack->get_visible_child());
      auto view = dynamic_cast<Gtk::TextView*>(tab->get_child());

      // Very simple-minded search implementation.
      auto buffer = view->get_buffer();
      Gtk::TextIter match_start;
      Gtk::TextIter match_end;
      if (buffer->begin().forward_search(text, Gtk::TextSearchFlags::CASE_INSENSITIVE,
          match_start, match_end))
      {
        buffer->select_range(match_start, match_end);
        view->scroll_to(match_start);
      }
    }

With the search bar, our application now looks like this:

Adding a search bar

Source Code

File: `exampleapplication.h` (For use with gtkmm 4)

    #include "../step4/exampleapplication.h"
    // Equal to the corresponding file in step4

File: `exampleappprefs.h` (For use with gtkmm 4)

    #include "../step5/exampleappprefs.h"
    // Equal to the corresponding file in step5

File: `exampleappwindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPWINDOW_H_
    #define GTKMM_EXAMPLEAPPWINDOW_H_

    #include <gtkmm.h>

    #define HAS_SEARCH_ENTRY2 GTKMM_CHECK_VERSION(4,13,2)

    class ExampleAppWindow : public Gtk::ApplicationWindow
    {
    public:
      ExampleAppWindow(BaseObjectType* cobject,
        const Glib::RefPtr<Gtk::Builder>& refBuilder);

      static ExampleAppWindow* create();

      void open_file_view(const Glib::RefPtr<Gio::File>& file);

    protected:
      // Signal handlers
      void on_search_text_changed();
      void on_visible_child_changed();

      Glib::RefPtr<Gtk::Builder> m_refBuilder;
      Glib::RefPtr<Gio::Settings> m_settings;
      Gtk::Stack* m_stack {nullptr};
      Gtk::ToggleButton* m_search {nullptr};
      Gtk::SearchBar* m_searchbar {nullptr};
    #if HAS_SEARCH_ENTRY2
      Gtk::SearchEntry2* m_searchentry {nullptr};
    #else
      Gtk::SearchEntry* m_searchentry {nullptr};
    #endif
      Gtk::MenuButton* m_gears {nullptr};
      Glib::RefPtr<Glib::Binding> m_prop_binding;
    };

    #endif /* GTKMM_EXAMPLEAPPWINDOW_H */

File: `exampleapplication.cc` (For use with gtkmm 4)

    #include "../step5/exampleapplication.cc"
    // Equal to the corresponding file in step5

File: `exampleappprefs.cc` (For use with gtkmm 4)

    #include "../step5/exampleappprefs.cc"
    // Equal to the corresponding file in step5

File: `exampleappwindow.cc` (For use with gtkmm 4)

    #include "exampleappwindow.h"
    #include <iostream>
    #include <stdexcept>

    ExampleAppWindow::ExampleAppWindow(BaseObjectType* cobject,
      const Glib::RefPtr<Gtk::Builder>& refBuilder)
    : Gtk::ApplicationWindow(cobject),
      m_refBuilder(refBuilder)
    {
      // Get widgets from the Gtk::Builder file.
      m_stack = m_refBuilder->get_widget<Gtk::Stack>("stack");
      if (!m_stack)
        throw std::runtime_error("No \"stack\" object in window.ui");

      m_search = m_refBuilder->get_widget<Gtk::ToggleButton>("search");
      if (!m_search)
        throw std::runtime_error("No \"search\" object in window.ui");

      m_searchbar = m_refBuilder->get_widget<Gtk::SearchBar>("searchbar");
      if (!m_searchbar)
        throw std::runtime_error("No \"searchbar\" object in window.ui");

    #if HAS_SEARCH_ENTRY2
      m_searchentry = m_refBuilder->get_widget<Gtk::SearchEntry2>("searchentry");
    #else
      m_searchentry = m_refBuilder->get_widget<Gtk::SearchEntry>("searchentry");
    #endif
      if (!m_searchentry)
        throw std::runtime_error("No \"searchentry\" object in window.ui");

      m_gears = m_refBuilder->get_widget<Gtk::MenuButton>("gears");
      if (!m_gears)
        throw std::runtime_error("No \"gears\" object in window.ui");

      // Bind settings.
      m_settings = Gio::Settings::create("org.gtkmm.exampleapp");
      m_settings->bind("transition", m_stack->property_transition_type());

      // Bind properties.
      m_prop_binding = Glib::Binding::bind_property(m_search->property_active(),
        m_searchbar->property_search_mode_enabled(), Glib::Binding::Flags::BIDIRECTIONAL);

      // Connect signal handlers.
      m_searchentry->signal_search_changed().connect(
        sigc::mem_fun(*this, &ExampleAppWindow::on_search_text_changed));
      m_stack->property_visible_child().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleAppWindow::on_visible_child_changed));

      // Connect the menu to the MenuButton m_gears.
      // (The connection between action and menu item is specified in gears_menu.ui.)
      auto menu_builder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/gears_menu.ui");
      auto menu = menu_builder->get_object<Gio::MenuModel>("menu");
      if (!menu)
        throw std::runtime_error("No \"menu\" object in gears_menu.ui");

      m_gears->set_menu_model(menu);
    }

    //static
    ExampleAppWindow* ExampleAppWindow::create()
    {
      // Load the Builder file and instantiate its widgets.
      auto refBuilder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/window.ui");

      auto window = Gtk::Builder::get_widget_derived<ExampleAppWindow>(refBuilder, "app_window");
      if (!window)
        throw std::runtime_error("No \"app_window\" object in window.ui");

      return window;
    }

    void ExampleAppWindow::open_file_view(const Glib::RefPtr<Gio::File>& file)
    {
      const Glib::ustring basename = file->get_basename();

      auto scrolled = Gtk::make_managed<Gtk::ScrolledWindow>();
      scrolled->set_expand(true);
      auto view = Gtk::make_managed<Gtk::TextView>();
      view->set_editable(false);
      view->set_cursor_visible(false);
      scrolled->set_child(*view);
      m_stack->add(*scrolled, basename, basename);

      auto buffer = view->get_buffer();
      try
      {
        char* contents = nullptr;
        gsize length = 0;

        file->load_contents(contents, length);
        buffer->set_text(contents, contents+length);
        g_free(contents);
      }
      catch (const Glib::Error& ex)
      {
        std::cout << "ExampleAppWindow::open_file_view(\"" << file->get_parse_name()
          << "\"):\n  " << ex.what() << std::endl;
        return;
      }

      auto tag = buffer->create_tag();
      m_settings->bind("font", tag->property_font());
      buffer->apply_tag(tag, buffer->begin(), buffer->end());

      m_search->set_sensitive(true);
    }

    void ExampleAppWindow::on_search_text_changed()
    {
      const auto text = m_searchentry->get_text();
      if (text.empty())
        return;

      auto tab = dynamic_cast<Gtk::ScrolledWindow*>(m_stack->get_visible_child());
      if (!tab)
      {
        std::cout << "ExampleAppWindow::on_search_text_changed(): No visible child." << std::endl;
        return;
      }

      auto view = dynamic_cast<Gtk::TextView*>(tab->get_child());
      if (!view)
      {
        std::cout << "ExampleAppWindow::on_search_text_changed(): No visible text view." << std::endl;
        return;
      }

      // Very simple-minded search implementation.
      auto buffer = view->get_buffer();
      Gtk::TextIter match_start;
      Gtk::TextIter match_end;
      if (buffer->begin().forward_search(text, Gtk::TextSearchFlags::CASE_INSENSITIVE,
          match_start, match_end))
      {
        buffer->select_range(match_start, match_end);
        view->scroll_to(match_start);
      }
    }

    void ExampleAppWindow::on_visible_child_changed()
    {
      m_searchbar->set_search_mode(false);
    }

File: `main.cc` (For use with gtkmm 4)

    #include "exampleapplication.h"
    #include "exampleappwindow.h"

    int main(int argc, char* argv[])
    {
    #if HAS_SEARCH_ENTRY2
      // A GtkSearchEntry (e.g. from window.ui) shall be wrapped in
      // a Gtk::SearhcEntry2 and not in a deprecated Gtk::SearchEntry.
      Gtk::Application::wrap_in_search_entry2(true);
    #endif

      // Since this example is running uninstalled, we have to help it find its
      // schema. This is *not* necessary in a properly installed application.
      Glib::setenv ("GSETTINGS_SCHEMA_DIR", ".", false);

      auto application = ExampleApplication::create();

      // Start the application, showing the initial window,
      // and opening extra views for any files that it is asked to open,
      // for instance as a command-line parameter.
      // run() will return when the last window has been closed.
      return application->run(argc, argv);
    }

File: `window.ui` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <interface>
      <object class="GtkApplicationWindow" id="app_window">
        <property name="title" translatable="yes">Example Application</property>
        <property name="default-width">600</property>
        <property name="default-height">400</property>
        <child type="titlebar">
          <object class="GtkHeaderBar" id="header">
            <child type="title">
              <object class="GtkStackSwitcher" id="tabs">
                <property name="stack">stack</property>
              </object>
            </child>
            <child type="end">
              <object class="GtkMenuButton" id="gears">
                <property name="direction">none</property>
              </object>
            </child>
            <child type="end">
              <object class="GtkToggleButton" id="search">
                <property name="sensitive">False</property>
                <property name="icon-name">edit-find-symbolic</property>
              </object>
            </child>
          </object>
        </child>
        <child>
          <object class="GtkBox" id="content_box">
            <property name="orientation">vertical</property>
            <child>
              <object class="GtkSearchBar" id="searchbar">
                <child>
                  <object class="GtkSearchEntry" id="searchentry">
                  </object>
                </child>
              </object>
            </child>
            <child>
              <object class="GtkStack" id="stack">
                <property name="transition-duration">500</property>
              </object>
            </child>
          </object>
        </child>
      </object>
    </interface>

### Adding a side bar

As another piece of functionality, we are adding a sidebar, which demonstrates Gtk::Revealer and Gtk::ListBox. The new widgets are added in the `window.ui` file.

The code to populate the sidebar with buttons for the words found in each file is a little too involved to go into here. But we'll look at the code to add a checkbutton for the new feature to the menu. A menu item is added to the ui file `gears_menu.ui`.

To connect the menu item to the new `show-words` setting, we use a Gio::Action corresponding to the given Gio::Settings key. In ExampleAppWindow's constructor:

    // Connect the menu to the MenuButton m_gears, and bind the show-words setting
    // to the win.show-words action and the "Words" menu item.
    // (The connection between action and menu item is specified in gears_menu.ui.)
    auto menu_builder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/gears_menu.ui");
    auto menu = menu_builder->get_object<Gio::MenuModel>("menu");
    m_gears->set_menu_model(menu);
    add_action(m_settings->create_action("show-words"));

What our application looks like now:

Adding a side bar

Source Code

File: `exampleapplication.h` (For use with gtkmm 4)

    #include "../step4/exampleapplication.h"
    // Equal to the corresponding file in step4

File: `exampleappprefs.h` (For use with gtkmm 4)

    #include "../step5/exampleappprefs.h"
    // Equal to the corresponding file in step5

File: `exampleappwindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPWINDOW_H_
    #define GTKMM_EXAMPLEAPPWINDOW_H_

    #include <gtkmm.h>

    #define HAS_SEARCH_ENTRY2 GTKMM_CHECK_VERSION(4,13,2)

    class ExampleAppWindow : public Gtk::ApplicationWindow
    {
    public:
      ExampleAppWindow(BaseObjectType* cobject,
        const Glib::RefPtr<Gtk::Builder>& refBuilder);

      static ExampleAppWindow* create();

      void open_file_view(const Glib::RefPtr<Gio::File>& file);

    protected:
      // Signal handlers
      void on_search_text_changed();
      void on_visible_child_changed();
      void on_find_word(const Gtk::Button* button);
      void on_reveal_child_changed();

      void update_words();

      Glib::RefPtr<Gtk::Builder> m_refBuilder;
      Glib::RefPtr<Gio::Settings> m_settings;
      Gtk::Stack* m_stack {nullptr};
      Gtk::ToggleButton* m_search {nullptr};
      Gtk::SearchBar* m_searchbar {nullptr};
    #if HAS_SEARCH_ENTRY2
      Gtk::SearchEntry2* m_searchentry {nullptr};
    #else
      Gtk::SearchEntry* m_searchentry {nullptr};
    #endif
      Gtk::MenuButton* m_gears {nullptr};
      Gtk::Revealer* m_sidebar {nullptr};
      Gtk::ListBox* m_words {nullptr};
      Glib::RefPtr<Glib::Binding> m_prop_binding;
    };

    #endif /* GTKMM_EXAMPLEAPPWINDOW_H */

File: `exampleapplication.cc` (For use with gtkmm 4)

    #include "../step5/exampleapplication.cc"
    // Equal to the corresponding file in step5

File: `exampleappprefs.cc` (For use with gtkmm 4)

    #include "../step5/exampleappprefs.cc"
    // Equal to the corresponding file in step5

File: `exampleappwindow.cc` (For use with gtkmm 4)

    #include "exampleappwindow.h"
    #include <iostream>
    #include <stdexcept>
    #include <set>

    ExampleAppWindow::ExampleAppWindow(BaseObjectType* cobject,
      const Glib::RefPtr<Gtk::Builder>& refBuilder)
    : Gtk::ApplicationWindow(cobject),
      m_refBuilder(refBuilder)
    {
      // Get widgets from the Gtk::Builder file.
      m_stack = m_refBuilder->get_widget<Gtk::Stack>("stack");
      if (!m_stack)
        throw std::runtime_error("No \"stack\" object in window.ui");

      m_search = m_refBuilder->get_widget<Gtk::ToggleButton>("search");
      if (!m_search)
        throw std::runtime_error("No \"search\" object in window.ui");

      m_searchbar = m_refBuilder->get_widget<Gtk::SearchBar>("searchbar");
      if (!m_searchbar)
        throw std::runtime_error("No \"searchbar\" object in window.ui");

    #if HAS_SEARCH_ENTRY2
      m_searchentry = m_refBuilder->get_widget<Gtk::SearchEntry2>("searchentry");
    #else
      m_searchentry = m_refBuilder->get_widget<Gtk::SearchEntry>("searchentry");
    #endif
      if (!m_searchentry)
        throw std::runtime_error("No \"searchentry\" object in window.ui");

      m_gears = m_refBuilder->get_widget<Gtk::MenuButton>("gears");
      if (!m_gears)
        throw std::runtime_error("No \"gears\" object in window.ui");

      m_sidebar = m_refBuilder->get_widget<Gtk::Revealer>("sidebar");
      if (!m_sidebar)
        throw std::runtime_error("No \"sidebar\" object in window.ui");

      m_words = m_refBuilder->get_widget<Gtk::ListBox>("words");
      if (!m_words)
        throw std::runtime_error("No \"words\" object in window.ui");

      // Bind settings.
      m_settings = Gio::Settings::create("org.gtkmm.exampleapp");
      m_settings->bind("transition", m_stack->property_transition_type());
      m_settings->bind("show-words", m_sidebar->property_reveal_child());

      // Bind properties.
      m_prop_binding = Glib::Binding::bind_property(m_search->property_active(),
        m_searchbar->property_search_mode_enabled(), Glib::Binding::Flags::BIDIRECTIONAL);

      // Connect signal handlers.
      m_searchentry->signal_search_changed().connect(
        sigc::mem_fun(*this, &ExampleAppWindow::on_search_text_changed));
      m_stack->property_visible_child().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleAppWindow::on_visible_child_changed));
      m_sidebar->property_reveal_child().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleAppWindow::on_reveal_child_changed));

      // Connect the menu to the MenuButton m_gears, and bind the show-words setting
      // to the win.show-words action and the "Words" menu item.
      // (The connection between action and menu item is specified in gears_menu.ui.)
      auto menu_builder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/gears_menu.ui");
      auto menu = menu_builder->get_object<Gio::MenuModel>("menu");
      if (!menu)
        throw std::runtime_error("No \"menu\" object in gears_menu.ui");

      m_gears->set_menu_model(menu);
      add_action(m_settings->create_action("show-words"));
    }

    //static
    ExampleAppWindow* ExampleAppWindow::create()
    {
      // Load the Builder file and instantiate its widgets.
      auto refBuilder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/window.ui");

      auto window = Gtk::Builder::get_widget_derived<ExampleAppWindow>(refBuilder, "app_window");
      if (!window)
        throw std::runtime_error("No \"app_window\" object in window.ui");

      return window;
    }

    void ExampleAppWindow::open_file_view(const Glib::RefPtr<Gio::File>& file)
    {
      const Glib::ustring basename = file->get_basename();

      auto scrolled = Gtk::make_managed<Gtk::ScrolledWindow>();
      scrolled->set_expand(true);
      auto view = Gtk::make_managed<Gtk::TextView>();
      view->set_editable(false);
      view->set_cursor_visible(false);
      scrolled->set_child(*view);
      m_stack->add(*scrolled, basename, basename);

      auto buffer = view->get_buffer();
      try
      {
        char* contents = nullptr;
        gsize length = 0;

        file->load_contents(contents, length);
        buffer->set_text(contents, contents+length);
        g_free(contents);
      }
      catch (const Glib::Error& ex)
      {
        std::cout << "ExampleAppWindow::open_file_view(\"" << file->get_parse_name()
          << "\"):\n  " << ex.what() << std::endl;
        return;
      }

      auto tag = buffer->create_tag();
      m_settings->bind("font", tag->property_font());
      buffer->apply_tag(tag, buffer->begin(), buffer->end());

      m_search->set_sensitive(true);
      update_words();
    }

    void ExampleAppWindow::on_search_text_changed()
    {
      const auto text = m_searchentry->get_text();
      if (text.empty())
        return;

      auto tab = dynamic_cast<Gtk::ScrolledWindow*>(m_stack->get_visible_child());
      if (!tab)
      {
        std::cout << "ExampleAppWindow::on_search_text_changed(): No visible child." << std::endl;
        return;
      }

      auto view = dynamic_cast<Gtk::TextView*>(tab->get_child());
      if (!view)
      {
        std::cout << "ExampleAppWindow::on_search_text_changed(): No visible text view." << std::endl;
        return;
      }

      // Very simple-minded search implementation.
      auto buffer = view->get_buffer();
      Gtk::TextIter match_start;
      Gtk::TextIter match_end;
      if (buffer->begin().forward_search(text, Gtk::TextSearchFlags::CASE_INSENSITIVE,
          match_start, match_end))
      {
        buffer->select_range(match_start, match_end);
        view->scroll_to(match_start);
      }
    }

    void ExampleAppWindow::on_visible_child_changed()
    {
      m_searchbar->set_search_mode(false);
      update_words();
    }

    void ExampleAppWindow::on_find_word(const Gtk::Button* button)
    {
      m_searchentry->set_text(button->get_label());
    }

    void ExampleAppWindow::on_reveal_child_changed()
    {
      update_words();
    }

    void ExampleAppWindow::update_words()
    {
      auto tab = dynamic_cast<Gtk::ScrolledWindow*>(m_stack->get_visible_child());
      if (!tab)
        return;

      auto view = dynamic_cast<Gtk::TextView*>(tab->get_child());
      if (!view)
      {
        std::cout << "ExampleAppWindow::update_words(): No visible text view." << std::endl;
        return;
      }
      auto buffer = view->get_buffer();

      // Find all words in the text buffer.
      std::set<Glib::ustring> words;
      auto start = buffer->begin();
      Gtk::TextIter end;
      while (start)
      {
        while (start && !start.starts_word())
          ++start;

        if (!start)
          break;

        end = start;
        end.forward_word_end();
        if (start == end)
          break;

        auto word = buffer->get_text(start, end, false);
        words.insert(word.lowercase());
        start = end;
      }

      // Remove old children from the ListBox.
      while (auto child = m_words->get_first_child())
        m_words->remove(*child);

      // Add new child buttons, one per unique word.
      for (const auto& word : words)
      {
        auto row = Gtk::make_managed<Gtk::Button>(word);
        row->signal_clicked().connect(sigc::bind(sigc::mem_fun(*this,
          &ExampleAppWindow::on_find_word), row));
        m_words->append(*row);
      }
    }

File: `main.cc` (For use with gtkmm 4)

    #include "../step6/main.cc"
    // Equal to the corresponding file in step6

File: `gears_menu.ui` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <interface>
      <menu id="menu">
        <section>
          <item>
            <attribute name="label" translatable="yes">_Words</attribute>
            <attribute name="action">win.show-words</attribute>
          </item>
          <item>
            <attribute name="label" translatable="yes">_Preferences</attribute>
            <attribute name="action">app.preferences</attribute>
          </item>
        </section>
        <section>
          <item>
            <attribute name="label" translatable="yes">_Quit</attribute>
            <attribute name="action">app.quit</attribute>
          </item>
        </section>
      </menu>
    </interface>

File: `window.ui` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <interface>
      <object class="GtkApplicationWindow" id="app_window">
        <property name="title" translatable="yes">Example Application</property>
        <property name="default-width">600</property>
        <property name="default-height">400</property>
        <child type="titlebar">
          <object class="GtkHeaderBar" id="header">
            <child type="title">
              <object class="GtkStackSwitcher" id="tabs">
                <property name="stack">stack</property>
              </object>
            </child>
            <child type="end">
              <object class="GtkToggleButton" id="search">
                <property name="sensitive">False</property>
                <property name="icon-name">edit-find-symbolic</property>
              </object>
            </child>
            <child type="end">
              <object class="GtkMenuButton" id="gears">
                <property name="direction">none</property>
              </object>
            </child>
          </object>
        </child>
        <child>
          <object class="GtkBox" id="content_box">
            <property name="orientation">vertical</property>
            <child>
              <object class="GtkSearchBar" id="searchbar">
                <child>
                  <object class="GtkSearchEntry" id="searchentry">
                  </object>
                </child>
              </object>
            </child>
            <child>
              <object class="GtkBox" id="hbox">
                <child>
                  <object class="GtkRevealer" id="sidebar">
                    <property name="transition-type">slide-right</property>
                    <child>
                     <object class="GtkScrolledWindow" id="sidebar-sw">
                       <property name="hscrollbar-policy">never</property>
                       <child>
                         <object class="GtkListBox" id="words">
                           <property name="selection-mode">none</property>
                         </object>
                       </child>
                     </object>
                    </child>
                  </object>
                </child>
                <child>
                  <object class="GtkStack" id="stack">
                    <property name="transition-duration">500</property>
                  </object>
                </child>
              </object>
            </child>
          </object>
        </child>
      </object>
    </interface>

File: `org.gtkmm.exampleapp.gschema.xml` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <schemalist>
      <schema path="/org/gtkmm/exampleapp/" id="org.gtkmm.exampleapp">
        <key name="font" type="s">
          <default>'Monospace 12'</default>
          <summary>Font</summary>
          <description>The font to be used for content.</description>
        </key>
        <key name="transition" type="s">
          <choices>
            <choice value='none'/>
            <choice value='crossfade'/>
            <choice value='slide-left-right'/>
          </choices>
          <default>'none'</default>
          <summary>Transition</summary>
          <description>The transition to use when switching tabs.</description>
        </key>
        <key name="show-words" type="b">
          <default>false</default>
          <summary>Show words</summary>
          <description>Whether to show a word list in the sidebar.</description>
        </key>
      </schema>
    </schemalist>

### Properties

Widgets and other objects have many useful properties. Here we show some ways to use them in new and flexible ways, by wrapping them in actions with Gio::PropertyAction or by binding them with Glib::Binding.

To set this up, we add two labels to the header bar in our `window.ui` file, named `lines_label` and `lines`, and get pointers to them in the application window's constructor, as we've seen a couple of times by now. We add a new "Lines" menu item to the gears menu, which triggers the `show-lines` action.

To make this menu item do something, we create a property action for the `visible` property of the `lines` label, and add it to the actions of the window. The effect of this is that the visibility of the label gets toggled every time the action is activated. Since we want both labels to appear and disappear together, we bind the `visible` property of the `lines_label` widget to the same property of the `lines` widget. In ExampleAppWindow's constructor:

    add_action(Gio::PropertyAction::create("show-lines", m_lines->property_visible()));
    m_binding_lines_visible = Glib::Binding::bind_property(m_lines->property_visible(),
      m_lines_label->property_visible());

We also need a function that counts the lines of the currently active tab, and updates the `lines` label. See the full source if you are interested in the details.

This brings our example application to this appearance:

Properties

Source Code

File: `exampleapplication.h` (For use with gtkmm 4)

    #include "../step4/exampleapplication.h"
    // Equal to the corresponding file in step4

File: `exampleappprefs.h` (For use with gtkmm 4)

    #include "../step5/exampleappprefs.h"
    // Equal to the corresponding file in step5

File: `exampleappwindow.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLEAPPWINDOW_H_
    #define GTKMM_EXAMPLEAPPWINDOW_H_

    #include <gtkmm.h>

    #define HAS_SEARCH_ENTRY2 GTKMM_CHECK_VERSION(4,13,2)

    class ExampleAppWindow : public Gtk::ApplicationWindow
    {
    public:
      ExampleAppWindow(BaseObjectType* cobject,
        const Glib::RefPtr<Gtk::Builder>& refBuilder);

      static ExampleAppWindow* create();

      void open_file_view(const Glib::RefPtr<Gio::File>& file);

    protected:
      // Signal handlers
      void on_search_text_changed();
      void on_visible_child_changed();
      void on_find_word(const Gtk::Button* button);
      void on_reveal_child_changed();

      void update_words();
      void update_lines();

      Glib::RefPtr<Gtk::Builder> m_refBuilder;
      Glib::RefPtr<Gio::Settings> m_settings;
      Gtk::Stack* m_stack {nullptr};
      Gtk::ToggleButton* m_search {nullptr};
      Gtk::SearchBar* m_searchbar {nullptr};
    #if HAS_SEARCH_ENTRY2
      Gtk::SearchEntry2* m_searchentry {nullptr};
    #else
      Gtk::SearchEntry* m_searchentry {nullptr};
    #endif
      Gtk::MenuButton* m_gears {nullptr};
      Gtk::Revealer* m_sidebar {nullptr};
      Gtk::ListBox* m_words {nullptr};
      Gtk::Label* m_lines {nullptr};
      Gtk::Label* m_lines_label {nullptr};
      Glib::RefPtr<Glib::Binding> m_binding_search_enabled;
      Glib::RefPtr<Glib::Binding> m_binding_lines_visible;
    };

    #endif /* GTKMM_EXAMPLEAPPWINDOW_H */

File: `exampleapplication.cc` (For use with gtkmm 4)

    #include "../step5/exampleapplication.cc"
    // Equal to the corresponding file in step5

File: `exampleappprefs.cc` (For use with gtkmm 4)

    #include "../step5/exampleappprefs.cc"
    // Equal to the corresponding file in step5

File: `exampleappwindow.cc` (For use with gtkmm 4)

    #include "exampleappwindow.h"
    #include <iostream>
    #include <stdexcept>
    #include <set>

    ExampleAppWindow::ExampleAppWindow(BaseObjectType* cobject,
      const Glib::RefPtr<Gtk::Builder>& refBuilder)
    : Gtk::ApplicationWindow(cobject),
      m_refBuilder(refBuilder)
    {
      // Get widgets from the Gtk::Builder file.
      m_stack = m_refBuilder->get_widget<Gtk::Stack>("stack");
      if (!m_stack)
        throw std::runtime_error("No \"stack\" object in window.ui");

      m_search = m_refBuilder->get_widget<Gtk::ToggleButton>("search");
      if (!m_search)
        throw std::runtime_error("No \"search\" object in window.ui");

      m_searchbar = m_refBuilder->get_widget<Gtk::SearchBar>("searchbar");
      if (!m_searchbar)
        throw std::runtime_error("No \"searchbar\" object in window.ui");

    #if HAS_SEARCH_ENTRY2
      m_searchentry = m_refBuilder->get_widget<Gtk::SearchEntry2>("searchentry");
    #else
      m_searchentry = m_refBuilder->get_widget<Gtk::SearchEntry>("searchentry");
    #endif
      if (!m_searchentry)
        throw std::runtime_error("No \"searchentry\" object in window.ui");

      m_gears = m_refBuilder->get_widget<Gtk::MenuButton>("gears");
      if (!m_gears)
        throw std::runtime_error("No \"gears\" object in window.ui");

      m_sidebar = m_refBuilder->get_widget<Gtk::Revealer>("sidebar");
      if (!m_sidebar)
        throw std::runtime_error("No \"sidebar\" object in window.ui");

      m_words = m_refBuilder->get_widget<Gtk::ListBox>("words");
      if (!m_words)
        throw std::runtime_error("No \"words\" object in window.ui");

      m_lines = m_refBuilder->get_widget<Gtk::Label>("lines");
      if (!m_lines)
        throw std::runtime_error("No \"lines\" object in window.ui");

      m_lines_label = m_refBuilder->get_widget<Gtk::Label>("lines_label");
      if (!m_lines_label)
        throw std::runtime_error("No \"lines_label\" object in window.ui");

      // Bind settings.
      m_settings = Gio::Settings::create("org.gtkmm.exampleapp");
      m_settings->bind("transition", m_stack->property_transition_type());
      m_settings->bind("show-words", m_sidebar->property_reveal_child());

      // Bind properties of the search button to the search bar.
      m_binding_search_enabled = Glib::Binding::bind_property(m_search->property_active(),
        m_searchbar->property_search_mode_enabled(), Glib::Binding::Flags::BIDIRECTIONAL);

      // Connect signal handlers.
      m_searchentry->signal_search_changed().connect(
        sigc::mem_fun(*this, &ExampleAppWindow::on_search_text_changed));
      m_stack->property_visible_child().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleAppWindow::on_visible_child_changed));
      m_sidebar->property_reveal_child().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleAppWindow::on_reveal_child_changed));

      // Connect the menu to the MenuButton m_gears, and bind the show-words setting
      // to the win.show-words action and the "Words" menu item.
      // (The connection between action and menu item is specified in gears_menu.ui.)
      auto menu_builder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/gears_menu.ui");
      auto menu = menu_builder->get_object<Gio::MenuModel>("menu");
      if (!menu)
        throw std::runtime_error("No \"menu\" object in gears_menu.ui");

      m_gears->set_menu_model(menu);
      add_action(m_settings->create_action("show-words"));

      // Bind the "visible" property of m_lines to the win.show-lines action, to
      // the "Lines" menu item and to the "visible" property of m_lines_label.
      add_action(Gio::PropertyAction::create("show-lines", m_lines->property_visible()));
      m_binding_lines_visible = Glib::Binding::bind_property(m_lines->property_visible(),
        m_lines_label->property_visible());
    }

    //static
    ExampleAppWindow* ExampleAppWindow::create()
    {
      // Load the Builder file and instantiate its widgets.
      auto refBuilder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/window.ui");

      auto window = Gtk::Builder::get_widget_derived<ExampleAppWindow>(refBuilder, "app_window");
      if (!window)
        throw std::runtime_error("No \"app_window\" object in window.ui");

      return window;
    }

    void ExampleAppWindow::open_file_view(const Glib::RefPtr<Gio::File>& file)
    {
      const Glib::ustring basename = file->get_basename();

      auto scrolled = Gtk::make_managed<Gtk::ScrolledWindow>();
      scrolled->set_expand(true);
      auto view = Gtk::make_managed<Gtk::TextView>();
      view->set_editable(false);
      view->set_cursor_visible(false);
      scrolled->set_child(*view);
      m_stack->add(*scrolled, basename, basename);

      auto buffer = view->get_buffer();
      try
      {
        char* contents = nullptr;
        gsize length = 0;

        file->load_contents(contents, length);
        buffer->set_text(contents, contents+length);
        g_free(contents);
      }
      catch (const Glib::Error& ex)
      {
        std::cout << "ExampleAppWindow::open_file_view(\"" << file->get_parse_name()
          << "\"):\n  " << ex.what() << std::endl;
        return;
      }

      auto tag = buffer->create_tag();
      m_settings->bind("font", tag->property_font());
      buffer->apply_tag(tag, buffer->begin(), buffer->end());

      m_search->set_sensitive(true);
      update_words();
      update_lines();
    }

    void ExampleAppWindow::on_search_text_changed()
    {
      const auto text = m_searchentry->get_text();
      if (text.empty())
        return;

      auto tab = dynamic_cast<Gtk::ScrolledWindow*>(m_stack->get_visible_child());
      if (!tab)
      {
        std::cout << "ExampleAppWindow::on_search_text_changed(): No visible child." << std::endl;
        return;
      }

      auto view = dynamic_cast<Gtk::TextView*>(tab->get_child());
      if (!view)
      {
        std::cout << "ExampleAppWindow::on_search_text_changed(): No visible text view." << std::endl;
        return;
      }

      // Very simple-minded search implementation.
      auto buffer = view->get_buffer();
      Gtk::TextIter match_start;
      Gtk::TextIter match_end;
      if (buffer->begin().forward_search(text, Gtk::TextSearchFlags::CASE_INSENSITIVE,
          match_start, match_end))
      {
        buffer->select_range(match_start, match_end);
        view->scroll_to(match_start);
      }
    }

    void ExampleAppWindow::on_visible_child_changed()
    {
      m_searchbar->set_search_mode(false);
      update_words();
      update_lines();
    }

    void ExampleAppWindow::on_find_word(const Gtk::Button* button)
    {
      m_searchentry->set_text(button->get_label());
    }

    void ExampleAppWindow::on_reveal_child_changed()
    {
      update_words();
    }

    void ExampleAppWindow::update_words()
    {
      auto tab = dynamic_cast<Gtk::ScrolledWindow*>(m_stack->get_visible_child());
      if (!tab)
        return;

      auto view = dynamic_cast<Gtk::TextView*>(tab->get_child());
      if (!view)
      {
        std::cout << "ExampleAppWindow::update_words(): No visible text view." << std::endl;
        return;
      }
      auto buffer = view->get_buffer();

      // Find all words in the text buffer.
      std::set<Glib::ustring> words;
      auto start = buffer->begin();
      Gtk::TextIter end;
      while (start)
      {
        while (start && !start.starts_word())
          ++start;

        if (!start)
          break;

        end = start;
        end.forward_word_end();
        if (start == end)
          break;

        auto word = buffer->get_text(start, end, false);
        words.insert(word.lowercase());
        start = end;
      }

      // Remove old children from the ListBox.
      while (auto child = m_words->get_first_child())
        m_words->remove(*child);

      // Add new child buttons, one per unique word.
      for (const auto& word : words)
      {
        auto row = Gtk::make_managed<Gtk::Button>(word);
        row->signal_clicked().connect(sigc::bind(sigc::mem_fun(*this,
          &ExampleAppWindow::on_find_word), row));
        m_words->append(*row);
      }
    }

    void ExampleAppWindow::update_lines()
    {
      auto tab = dynamic_cast<Gtk::ScrolledWindow*>(m_stack->get_visible_child());
      if (!tab)
        return;

      auto view = dynamic_cast<Gtk::TextView*>(tab->get_child());
      if (!view)
      {
        std::cout << "ExampleAppWindow::update_lines(): No visible text view." << std::endl;
        return;
      }
      auto buffer = view->get_buffer();

      int count = 0;
      auto iter = buffer->begin();
      while (iter)
      {
        ++count;
        if (!iter.forward_line())
          break;
      }
      m_lines->set_text(Glib::ustring::format(count));
    }

File: `main.cc` (For use with gtkmm 4)

    #include "../step6/main.cc"
    // Equal to the corresponding file in step6

File: `gears_menu.ui` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <interface>
      <menu id="menu">
        <section>
          <item>
            <attribute name="label" translatable="yes">_Words</attribute>
            <attribute name="action">win.show-words</attribute>
          </item>
          <item>
            <attribute name="label" translatable="yes">_Lines</attribute>
            <attribute name="action">win.show-lines</attribute>
          </item>
          <item>
            <attribute name="label" translatable="yes">_Preferences</attribute>
            <attribute name="action">app.preferences</attribute>
          </item>
        </section>
        <section>
          <item>
            <attribute name="label" translatable="yes">_Quit</attribute>
            <attribute name="action">app.quit</attribute>
          </item>
        </section>
      </menu>
    </interface>

File: `window.ui` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <interface>
      <object class="GtkApplicationWindow" id="app_window">
        <property name="title" translatable="yes">Example Application</property>
        <property name="default-width">600</property>
        <property name="default-height">400</property>
        <child type="titlebar">
          <object class="GtkHeaderBar" id="header">
            <child>
              <object class="GtkLabel" id="lines_label">
                <property name="visible">False</property>
                <property name="label" translatable="yes">Lines:</property>
              </object>
            </child>
            <child>
              <object class="GtkLabel" id="lines">
                <property name="visible">False</property>
              </object>
            </child>
            <child type="title">
              <object class="GtkStackSwitcher" id="tabs">
                <property name="stack">stack</property>
              </object>
            </child>
            <child type="end">
              <object class="GtkToggleButton" id="search">
                <property name="sensitive">False</property>
                <property name="icon-name">edit-find-symbolic</property>
              </object>
            </child>
            <child type="end">
              <object class="GtkMenuButton" id="gears">
                <property name="direction">none</property>
              </object>
            </child>
          </object>
        </child>
        <child>
          <object class="GtkBox" id="content_box">
            <property name="orientation">vertical</property>
            <child>
              <object class="GtkSearchBar" id="searchbar">
                <child>
                  <object class="GtkSearchEntry" id="searchentry">
                  </object>
                </child>
              </object>
            </child>
            <child>
              <object class="GtkBox" id="hbox">
                <child>
                  <object class="GtkRevealer" id="sidebar">
                    <property name="transition-type">slide-right</property>
                    <child>
                      <object class="GtkScrolledWindow" id="sidebar-sw">
                        <property name="hscrollbar-policy">never</property>
                        <child>
                          <object class="GtkListBox" id="words">
                            <property name="selection-mode">none</property>
                          </object>
                        </child>
                      </object>
                    </child>
                  </object>
                </child>
                <child>
                  <object class="GtkStack" id="stack">
                    <property name="transition-duration">500</property>
                  </object>
                </child>
              </object>
            </child>
          </object>
        </child>
      </object>
    </interface>

### Header bar

Our application already uses a Gtk::HeaderBar instead of a 'normal' window titlebar. The header bar is a direct child of the window, and its type is `titlebar`. This is set in the `window.ui` file.

Here we'll just make two small changes to the header bar. The `decoration-layout` property is set in the `window.ui` file, to show only the close button, and hide the minimize and maximize buttons. We also include an icon in the resource file, and set up this icon as the window icon. In ExampleAppWindow's constructor:

    Gtk::IconTheme::get_for_display(get_display())->add_resource_path("/org/gtkmm/exampleapp");
    set_icon_name("exampleapp");

Here is how the application now looks:

Header bar

The `window.ui` file sets a header bar title, but this title is not shown. That's because the stack switcher is a child of type `title`. The stack switcher becomes a custom title that hides the title label.

Source Code

File: `exampleapplication.h` (For use with gtkmm 4)

    #include "../step4/exampleapplication.h"
    // Equal to the corresponding file in step4

File: `exampleappprefs.h` (For use with gtkmm 4)

    #include "../step5/exampleappprefs.h"
    // Equal to the corresponding file in step5

File: `exampleappwindow.h` (For use with gtkmm 4)

    #include "../step8/exampleappwindow.h"
    // Equal to the corresponding file in step8

File: `exampleapplication.cc` (For use with gtkmm 4)

    #include "../step5/exampleapplication.cc"
    // Equal to the corresponding file in step5

File: `exampleappprefs.cc` (For use with gtkmm 4)

    #include "../step5/exampleappprefs.cc"
    // Equal to the corresponding file in step5

File: `exampleappwindow.cc` (For use with gtkmm 4)

    #include "exampleappwindow.h"
    #include <iostream>
    #include <stdexcept>
    #include <set>

    ExampleAppWindow::ExampleAppWindow(BaseObjectType* cobject,
      const Glib::RefPtr<Gtk::Builder>& refBuilder)
    : Gtk::ApplicationWindow(cobject),
      m_refBuilder(refBuilder)
    {
      // Get widgets from the Gtk::Builder file.
      m_stack = m_refBuilder->get_widget<Gtk::Stack>("stack");
      if (!m_stack)
        throw std::runtime_error("No \"stack\" object in window.ui");

      m_search = m_refBuilder->get_widget<Gtk::ToggleButton>("search");
      if (!m_search)
        throw std::runtime_error("No \"search\" object in window.ui");

      m_searchbar = m_refBuilder->get_widget<Gtk::SearchBar>("searchbar");
      if (!m_searchbar)
        throw std::runtime_error("No \"searchbar\" object in window.ui");

    #if HAS_SEARCH_ENTRY2
      m_searchentry = m_refBuilder->get_widget<Gtk::SearchEntry2>("searchentry");
    #else
      m_searchentry = m_refBuilder->get_widget<Gtk::SearchEntry>("searchentry");
    #endif
      if (!m_searchentry)
        throw std::runtime_error("No \"searchentry\" object in window.ui");

      m_gears = m_refBuilder->get_widget<Gtk::MenuButton>("gears");
      if (!m_gears)
        throw std::runtime_error("No \"gears\" object in window.ui");

      m_sidebar = m_refBuilder->get_widget<Gtk::Revealer>("sidebar");
      if (!m_sidebar)
        throw std::runtime_error("No \"sidebar\" object in window.ui");

      m_words = m_refBuilder->get_widget<Gtk::ListBox>("words");
      if (!m_words)
        throw std::runtime_error("No \"words\" object in window.ui");

      m_lines = m_refBuilder->get_widget<Gtk::Label>("lines");
      if (!m_lines)
        throw std::runtime_error("No \"lines\" object in window.ui");

      m_lines_label = m_refBuilder->get_widget<Gtk::Label>("lines_label");
      if (!m_lines_label)
        throw std::runtime_error("No \"lines_label\" object in window.ui");

      // Bind settings.
      m_settings = Gio::Settings::create("org.gtkmm.exampleapp");
      m_settings->bind("transition", m_stack->property_transition_type());
      m_settings->bind("show-words", m_sidebar->property_reveal_child());

      // Bind properties of the search button to the search bar.
      m_binding_search_enabled = Glib::Binding::bind_property(m_search->property_active(),
        m_searchbar->property_search_mode_enabled(), Glib::Binding::Flags::BIDIRECTIONAL);

      // Connect signal handlers.
      m_searchentry->signal_search_changed().connect(
        sigc::mem_fun(*this, &ExampleAppWindow::on_search_text_changed));
      m_stack->property_visible_child().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleAppWindow::on_visible_child_changed));
      m_sidebar->property_reveal_child().signal_changed().connect(
        sigc::mem_fun(*this, &ExampleAppWindow::on_reveal_child_changed));

      // Connect the menu to the MenuButton m_gears, and bind the show-words setting
      // to the win.show-words action and the "Words" menu item.
      // (The connection between action and menu item is specified in gears_menu.ui.)
      auto menu_builder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/gears_menu.ui");
      auto menu = menu_builder->get_object<Gio::MenuModel>("menu");
      if (!menu)
        throw std::runtime_error("No \"menu\" object in gears_menu.ui");

      m_gears->set_menu_model(menu);
      add_action(m_settings->create_action("show-words"));

      // Bind the "visible" property of m_lines to the win.show-lines action, to
      // the "Lines" menu item and to the "visible" property of m_lines_label.
      add_action(Gio::PropertyAction::create("show-lines", m_lines->property_visible()));
      m_binding_lines_visible = Glib::Binding::bind_property(m_lines->property_visible(),
        m_lines_label->property_visible());

      // Set the window icon.
      Gtk::IconTheme::get_for_display(get_display())->add_resource_path("/org/gtkmm/exampleapp");
      set_icon_name("exampleapp");
    }

    //static
    ExampleAppWindow* ExampleAppWindow::create()
    {
      // Load the Builder file and instantiate its widgets.
      auto refBuilder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/window.ui");

      auto window = Gtk::Builder::get_widget_derived<ExampleAppWindow>(refBuilder, "app_window");
      if (!window)
        throw std::runtime_error("No \"app_window\" object in window.ui");

      return window;
    }

    void ExampleAppWindow::open_file_view(const Glib::RefPtr<Gio::File>& file)
    {
      const Glib::ustring basename = file->get_basename();

      auto scrolled = Gtk::make_managed<Gtk::ScrolledWindow>();
      scrolled->set_expand(true);
      auto view = Gtk::make_managed<Gtk::TextView>();
      view->set_editable(false);
      view->set_cursor_visible(false);
      scrolled->set_child(*view);
      m_stack->add(*scrolled, basename, basename);

      auto buffer = view->get_buffer();
      try
      {
        char* contents = nullptr;
        gsize length = 0;

        file->load_contents(contents, length);
        buffer->set_text(contents, contents+length);
        g_free(contents);
      }
      catch (const Glib::Error& ex)
      {
        std::cout << "ExampleAppWindow::open_file_view(\"" << file->get_parse_name()
          << "\"):\n  " << ex.what() << std::endl;
        return;
      }

      auto tag = buffer->create_tag();
      m_settings->bind("font", tag->property_font());
      buffer->apply_tag(tag, buffer->begin(), buffer->end());

      m_search->set_sensitive(true);
      update_words();
      update_lines();
    }

    void ExampleAppWindow::on_search_text_changed()
    {
      const auto text = m_searchentry->get_text();
      if (text.empty())
        return;

      auto tab = dynamic_cast<Gtk::ScrolledWindow*>(m_stack->get_visible_child());
      if (!tab)
      {
        std::cout << "ExampleAppWindow::on_search_text_changed(): No visible child." << std::endl;
        return;
      }

      auto view = dynamic_cast<Gtk::TextView*>(tab->get_child());
      if (!view)
      {
        std::cout << "ExampleAppWindow::on_search_text_changed(): No visible text view." << std::endl;
        return;
      }

      // Very simple-minded search implementation.
      auto buffer = view->get_buffer();
      Gtk::TextIter match_start;
      Gtk::TextIter match_end;
      if (buffer->begin().forward_search(text, Gtk::TextSearchFlags::CASE_INSENSITIVE,
          match_start, match_end))
      {
        buffer->select_range(match_start, match_end);
        view->scroll_to(match_start);
      }
    }

    void ExampleAppWindow::on_visible_child_changed()
    {
      m_searchbar->set_search_mode(false);
      update_words();
      update_lines();
    }

    void ExampleAppWindow::on_find_word(const Gtk::Button* button)
    {
      m_searchentry->set_text(button->get_label());
    }

    void ExampleAppWindow::on_reveal_child_changed()
    {
      update_words();
    }

    void ExampleAppWindow::update_words()
    {
      auto tab = dynamic_cast<Gtk::ScrolledWindow*>(m_stack->get_visible_child());
      if (!tab)
        return;

      auto view = dynamic_cast<Gtk::TextView*>(tab->get_child());
      if (!view)
      {
        std::cout << "ExampleAppWindow::update_words(): No visible text view." << std::endl;
        return;
      }
      auto buffer = view->get_buffer();

      // Find all words in the text buffer.
      std::set<Glib::ustring> words;
      auto start = buffer->begin();
      Gtk::TextIter end;
      while (start)
      {
        while (start && !start.starts_word())
          ++start;

        if (!start)
          break;

        end = start;
        end.forward_word_end();
        if (start == end)
          break;

        auto word = buffer->get_text(start, end, false);
        words.insert(word.lowercase());
        start = end;
      }

      // Remove old children from the ListBox.
      while (auto child = m_words->get_first_child())
        m_words->remove(*child);

      // Add new child buttons, one per unique word.
      for (const auto& word : words)
      {
        auto row = Gtk::make_managed<Gtk::Button>(word);
        row->signal_clicked().connect(sigc::bind(sigc::mem_fun(*this,
          &ExampleAppWindow::on_find_word), row));
        m_words->append(*row);
      }
    }

    void ExampleAppWindow::update_lines()
    {
      auto tab = dynamic_cast<Gtk::ScrolledWindow*>(m_stack->get_visible_child());
      if (!tab)
        return;

      auto view = dynamic_cast<Gtk::TextView*>(tab->get_child());
      if (!view)
      {
        std::cout << "ExampleAppWindow::update_lines(): No visible text view." << std::endl;
        return;
      }
      auto buffer = view->get_buffer();

      int count = 0;
      auto iter = buffer->begin();
      while (iter)
      {
        ++count;
        if (!iter.forward_line())
          break;
      }
      m_lines->set_text(Glib::ustring::format(count));
    }

File: `main.cc` (For use with gtkmm 4)

    #include "../step6/main.cc"
    // Equal to the corresponding file in step6

File: `exampleapp.gresource.xml` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <gresources>
      <gresource prefix="/org/gtkmm/exampleapp">
        <file preprocess="xml-stripblanks">window.ui</file>
        <file preprocess="xml-stripblanks">gears_menu.ui</file>
        <file preprocess="xml-stripblanks">prefs.ui</file>
        <file>exampleapp.png</file>
      </gresource>
    </gresources>

File: `window.ui` (For use with gtkmm 4)

    <?xml version="1.0" encoding="UTF-8"?>
    <interface>
      <object class="GtkApplicationWindow" id="app_window">
        <property name="title" translatable="yes">Example Application</property>
        <property name="default-width">600</property>
        <property name="default-height">400</property>
        <child type="titlebar">
          <object class="GtkHeaderBar" id="header">
            <property name="decoration-layout">icon:close</property>
            <child>
              <object class="GtkLabel" id="lines_label">
                <property name="visible">False</property>
                <property name="label" translatable="yes">Lines:</property>
              </object>
            </child>
            <child>
              <object class="GtkLabel" id="lines">
                <property name="visible">False</property>
              </object>
            </child>
            <child type="title">
              <object class="GtkStackSwitcher" id="tabs">
                <property name="stack">stack</property>
              </object>
            </child>
            <child type="end">
              <object class="GtkToggleButton" id="search">
                <property name="sensitive">False</property>
                <property name="icon-name">edit-find-symbolic</property>
              </object>
            </child>
            <child type="end">
              <object class="GtkMenuButton" id="gears">
                <property name="direction">none</property>
              </object>
            </child>
          </object>
        </child>
        <child>
          <object class="GtkBox" id="content_box">
            <property name="orientation">vertical</property>
            <child>
              <object class="GtkSearchBar" id="searchbar">
                <child>
                  <object class="GtkSearchEntry" id="searchentry">
                  </object>
                </child>
              </object>
            </child>
            <child>
              <object class="GtkBox" id="hbox">
                <child>
                  <object class="GtkRevealer" id="sidebar">
                    <property name="transition-type">slide-right</property>
                    <child>
                      <object class="GtkScrolledWindow" id="sidebar-sw">
                        <property name="hscrollbar-policy">never</property>
                        <child>
                          <object class="GtkListBox" id="words">
                            <property name="selection-mode">none</property>
                          </object>
                        </child>
                      </object>
                    </child>
                  </object>
                </child>
                <child>
                  <object class="GtkStack" id="stack">
                    <property name="transition-duration">500</property>
                  </object>
                </child>
              </object>
            </child>
          </object>
        </child>
      </object>
    </interface>

## Contributing

This document, like so much other great software out there, was created for free by volunteers. If you are at all knowledgeable about any aspect of gtkmm that does not already have documentation, please consider contributing to this document.

Ideally, we would like you to provide a merge request to the `docs/tutorial/C/index-in.docbook` file. This file is in the `gtkmm-documentation` module in GNOME git.

If you do decide to contribute, please post your contribution as an issue or merge request to GitLab. You can also discuss your ideas on GNOME's Discourse instance, under the Platform/Language bindings category with a `cplusplus` tag. Also, be aware that the entirety of this document is free, and any addition you provide must also be free. That is, people must be able to use any portion of your examples in their programs, and copies of this document (including your contribution) may be distributed freely.

## The RefPtr smartpointer

Glib::RefPtr is a smartpointer. Specifically, it is a reference-counting smartpointer. You might be familiar with std::unique_ptr<> and std::shared_ptr<>, which are also smartpointers. In gtkmm-4.0 Glib::RefPtr<> is an alias for std::shared_ptr<>, which is reference-counting. Glib::RefPtr<> was introduced long before there was a reference-counting smartpointer in the C++ Standard Library.

If you make your own Glib::ObjectBase-derived classes with create() methods that return a Glib::RefPtr, you must use `Glib::make_refptr_for_instance()` in your create() methods. This function creates a std::shared_ptr with a special deleter, which handles the reference-count for the wrapped C object.

Glib::RefPtr is not used for storing widgets derived from Gtk::Widget. Widgets have public constructors instead of protected constructors and create() methods.

Reference

A smartpointer acts much like a normal pointer. Here are a few examples.

### Copiando

You can copy RefPtrs, just like normal pointers. But unlike normal pointers, you don't need to worry about deleting the underlying instance.

    auto refPixbuf = Gdk::Pixbuf::create_from_file(filename);
    auto refPixbuf2 = refPixbuf;

Of course this means that you can store RefPtrs in standard containers, such as std::vector or std::list.

    std::list<Glib::RefPtr<Gdk::Pixbuf>> listPixbufs;
    auto refPixbuf = Gdk::Pixbuf::create_from_file(filename);
    listPixbufs.push_back(refPixbuf);

### Dereferencing

You can dereference a smartpointer with the -> operator, to call the methods of the underlying instance, just like a normal pointer.

    auto refPixbuf = Gdk::Pixbuf::create_from_file(filename);
    auto width = refPixbuf->get_width();

You can also use the * operator and the get() method to access the underlying instance, but it's usually a bad idea to do so. Unless you are careful, you can end up with a pointer or a reference which is not included in the reference count.

    auto refPixbuf = Gdk::Pixbuf::create_from_file(filename);
    auto& underlying = *refPixbuf; // Possible, but not recommended

### Casting

You can cast RefPtrs to base types, just like normal pointers.

    auto refStore = Gtk::TreeStore::create(columns);
    Glib::RefPtr<Gtk::TreeModel> refModel = refStore;

This means that any method which takes a const Glib::RefPtr<BaseType>& argument can also take a const Glib::RefPtr<DerivedType>&. The cast is implicit, just as it would be for a normal pointer.

You can also cast to a derived type, but the syntax is a little different than with a normal pointer.

    auto refStore = std::dynamic_pointer_cast<Gtk::TreeStore>(refModel);
    auto refStore2 = std::static_pointer_cast<Gtk::TreeStore>(refModel);

### Checking for nullptr

Just like normal pointers, you can check whether a RefPtr points to anything.

    auto refModel = m_TreeView.get_model();
    if (refModel)
    {
      auto cols_count = refModel->get_n_columns();
      ...
    }

But unlike normal pointers, RefPtrs are automatically initialized to `nullptr` so you don't need to remember to do that yourself.

### Constness

The use of the `const` keyword in C++ is not always clear. You might not realize that const Something* declares a pointer to a const Something. The pointer can be changed, but not the Something that it points to.

Therefore, the RefPtr equivalent of Something* for a method parameter is const Glib::RefPtr<Something>&, and the equivalent of const Something* is const Glib::RefPtr<const Something>&.

The `const ... &` around both is just for efficiency, like using const std::string& instead of std::string for a method parameter to avoid unnecessary copying.

## Sinais

### Conectando manipuladores de sinais

gtkmm widget classes have signal accessor methods, such as Gtk::Button::signal_clicked(), which allow you to connect your signal handler. Thanks to the flexibility of libsigc++, the callback library used by gtkmm, the signal handler can be almost any kind of function, but you will probably want to use a class method. Among GTK C coders, these signal handlers are often named callbacks.

Here's an example of a signal handler being connected to a signal:

    #include <gtkmm/button.h>

    void on_button_clicked()
    {
      std::cout << "Hello World" << std::endl;
    }

    class some_class
    {
    public:
      some_class
      {
        button.signal_clicked().connect(sigc::ptr_fun(&on_button_clicked));
      }
    private:
      Gtk::Button button {"Hello World"};
    };

There's rather a lot to think about in this (non-functional) code. First let's identify the parties involved:

- The signal handler is on_button_clicked().

- We're hooking it up to the Gtk::Button object called `button`.

- When the Button emits its `clicked` signal, on_button_clicked() will be called.

Now let's look at the connection again:

        ...
        button.signal_clicked().connect(sigc::ptr_fun(&on_button_clicked));
        ...

Note that we don't pass a pointer to on_button_clicked() directly to the signal's connect() method. Instead, we call `sigc::ptr_fun()`, and pass the result to connect().

`sigc::ptr_fun()` generates a sigc::slot. A slot is an object which looks and feels like a function, but is actually an object. These are also known as function objects, or functors. `sigc::ptr_fun()` generates a slot for a standalone function or static method. `sigc::mem_fun()` generates a slot for a member method of a particular instance.

A C++ lambda expression is a functor which can be implicitly converted to a sigc::slot in the call to connect(). A lambda expression can be used instead of `sigc::ptr_fun()`. It's also possible to use a lambda expression instead of `sigc::mem_fun()`, but then you won't get automatic disconnection of the signal handler when a sigc::trackable-derived object goes out of scope.

Here's a slightly larger example of slots in action:

    #include <gtkmm/button.h>

    void on_button_clicked()
    {
      std::cout << "Hello World" << std::endl;
    }

    class some_class
    {
    public:
      some_class
      {
        button.signal_clicked().connect(sigc::ptr_fun(&on_button_clicked));
        button.signal_clicked().connect(sigc::mem_fun(*this, &some_class::on_button_clicked));
      }
      void on_button_clicked();
    private:
      Gtk::Button button {"Hello World"};
    };

The first call to connect() is just like the one we saw last time; nothing new here.

The next is more interesting. `sigc::mem_fun()` is called with two arguments. The first argument is *this, which is the object that our new slot will be pointing at. The second argument is a pointer to one of its methods. This particular version of `sigc::mem_fun()` creates a slot which will, when "called", call the pointed-to method of the specified object.

Another thing to note about this example is that we made the call to connect() twice for the same signal object. This is perfectly fine - when the button is clicked, both signal handlers will be called.

We just told you that the button's `clicked` signal is expecting to call a method with no arguments. All signals have requirements like this - you can't hook a function with two arguments to a signal expecting none (unless you use an adapter, such as `sigc::bind()`, of course). Therefore, it's important to know what type of signal handler you'll be expected to connect to a given signal.

### Escrevendo manipuladores de sinais

To find out what type of signal handler you can connect to a signal, you can look it up in the reference documentation or the header file. Here's an example of a signal declaration you might see in the gtkmm headers:

    Glib::SignalProxy<bool(Gtk::DirectionType)> signal_focus()

Other than the signal's name (`focus`), the template arguments are important to note here. The first argument, bool, is the type that the signal handler should return; and the type within parentheses, Gtk::DirectionType, is the type of this signal's first, and only, argument. By looking at the reference documentation, you can see the names of the arguments too.

The same principles apply for signals which have more arguments. Here's one with three (taken from `<gtkmm/textbuffer.h>`):

    Glib::SignalProxy<void(TextBuffer::iterator&, const Glib::ustrin&, int)> signal_insert();

It follows the same form. The first type is void, so that should be our signal handler's return type. The following three types are the argument types, in order. Our signal handler's prototype could look like this:

    void on_insert(TextBuffer::iterator& pos, const Glib::ustring& text, int bytes)

### Desconectando manipuladores de sinais

Let's take another look at a Signal's `connect` method:

    sigc::connection signal<void(int)>::connect(const sigc::slot<void(int)>&);

The returned sigc::connection can be used to control the connection. By keeping a connection object you can disconnect its associated signal handler using the sigc::connection::disconnect() method.

### Overriding default signal handlers

So far we've told you to perform actions in response to button-presses and the like by handling signals. That's certainly a good way to do things, but it's not the only way.

Instead of laboriously connecting signal handlers to signals, you can simply make a new class which inherits from a widget - say, a Button - and then override the default signal handler, such as Button::on_clicked(). This can be a lot simpler than hooking up signal handlers for everything.

Subclassing isn't always the best way to accomplish things. It is only useful when you want the widget to handle its own signal by itself. If you want some other class to handle the signal then you'll need to connect a separate handler. This is even more true if you want several objects to handle the same signal, or if you want one signal handler to respond to the same signal from different objects.

gtkmm classes are designed with overriding in mind; they contain virtual member methods specifically intended to be overridden.

Let's look at an example of overriding:

    #include <gtkmm/button.h>

    class OverriddenButton : public Gtk::Button
    {
    protected:
      void on_clicked() override;
    }

    void OverriddenButton::on_clicked()
    {
      std::cout << "Hello World" << std::endl;

      // call the base class's version of the method:
      Gtk::Button::on_clicked();
    }

Here we define a new class called OverriddenButton, which inherits from Gtk::Button. The only thing we change is the on_clicked() method, which is called whenever Gtk::Button emits the `clicked` signal. This method prints "Hello World" to `stdout`, and then calls the original, overridden method, to let Gtk::Button do what it would have done had we not overridden.

You don't always need to call the parent's method; there are times when you might not want to. Note that we called the parent method after writing "Hello World", but we could have called it before. In this simple example, it hardly matters much, but there are times when it will. With connected signal handlers, it's not quite so easy to change details like this, and you can do something here which you can't do at all with connected signal handlers: you can call the parent method in the middle of your custom code.

### Ligando argumentos extras

If you use one signal handler to catch the same signal from several widgets, you might like that signal handler to receive some extra information. For instance, you might want to know which button was clicked. You can do this with `sigc::bind()`. Here's some code from the helloworld2 example.

    m_button1.signal_clicked().connect(sigc::bind(sigc::mem_fun(*this, &HelloWorld::on_button_clicked), "button 1"));

This says that we want the signal to send an extra Glib::ustring argument to the signal handler, and that the value of that argument should be "button 1". Of course we will need to add that extra argument to the declaration of our signal handler:

    void on_button_clicked(const Glib::ustring& data);

Of course, a normal "clicked" signal handler would have no arguments.

`sigc::bind()` is not commonly used, but you might find it helpful sometimes. If you are familiar with GTK programming then you have probably noticed that this is similar to the extra `gpointer data` arguments which all GTK callbacks have. This is generally overused in GTK to pass information that should be stored as member data in a derived widget, but widget derivation is very difficult in C. We have far less need of this hack in gtkmm.

### Event signals

Event signals are emitted as a result of some user input, for instance a key press or a mouse motion. Usually you don't handle these events directly. Instead, you use a subclass of Gtk::EventController, such as Gtk::EventControllerKey or Gtk::GestureClick. Event controllers can be added to a widget with Gtk::Widget::add_controller().

You might occasionally find it useful to handle events when there's something you can't accomplish with normal signals. Gtk::Button, for example, does not send mouse-pointer coordinates with its `clicked` signal, but you could handle Gtk::GestureClick::signal_pressed() if you needed this information. Gtk::EventControllerKey::signal_key_pressed() is often used to handle key-presses.

Some event controller signals behave slightly differently. The value returned from the signal handler indicates whether it has fully "handled" the event. If the value is `false` then gtkmm will pass the event on to the next signal handler. If the value is `true` then no other signal handlers will need to be called.

Handling an event doesn't affect the Widget's other signals. If you handle Gtk::GestureClick::signal_pressed() for Gtk::Button, you'll still be able to get the `clicked` signal. They are emitted at (nearly) the same time.

Here's a simple example:

    void on_button_press(int n_press, double x, double y);
    Gtk::Button button("label");
    auto controller = Gtk::GestureClick::create();
    controller->set_propagation_phase(Gtk::PropagationPhase::CAPTURE);
    controller->signal_pressed().connect(sigc::ptr_fun(&on_button_press));
    button.add_controller(controller);

When the mouse is over the button and a mouse button is pressed, on_button_press() will be called.

The call to set_propagation_phase() is necessary in this case because the GtkButton C class adds an event controller, handling button clicks in the capture phase. GtkButton claims the event, meaning that the event is not propagated in the bubble phase, where event controllers handle events by default.

#### Sequência de manipulador de sinal

By default, signal handlers that return void are called after any previously-connected signal handlers. However, this can be a problem with event signals that can stop event propagation by returning `true`. For instance, the existing signal handlers, or the default signal handler, might return `true` to stop other signal handlers from being called. To specify that your signal handler should be called before the other signal handlers, you can specify `false` for the `after` parameter. This connect() parameter is optional, if the signal handler returns void. For instance,

    key_controller->signal_key_pressed().connect(sigc::ptr_fun(&on_mywindow_key_pressed), false);

The event is propagated between widgets in 3 phases.

1. Capture phase - runs from the toplevel down to the event widget.

2. Target phase - runs only on the event widget.

3. Bubble phase - runs from the event widget up to the toplevel.

The Input Handling chapter in the GTK documentation describes user input handling in more detail.

### Exceptions in signal handlers

When a program is aborted because of an unhandled C++ exception, it's sometimes possible to use a debugger to find the location where the exception was thrown. This is more difficult than usual if the exception was thrown from a signal handler.

This section describes primarily what you can expect on a Linux system, when you use the gdb debugger.

First, let's look at a simple example where an exception is thrown from a normal function (no signal handler).

    // without_signal.cc
    #include <gtkmm.h>

    bool throwSomething()
    {
      throw "Something";
      return true;
    }

    int main(int argc, char** argv)
    {
      throwSomething();
      auto app = Gtk::Application::create("org.gtkmm.without_signal");
      return app->run();
    }

Here is an excerpt from a gdb session. Only the most interesting parts of the output are shown.

    > gdb without_signal
    (gdb) run
    terminate called after throwing an instance of 'char const*'

    Program received signal SIGABRT, Aborted.
    (gdb) backtrace
    #7  0x08048864 in throwSomething () at without_signal.cc:6
    #8  0x0804887d in main (argc=1, argv=0xbfffecd4) at without_signal.cc:12

You can see that the exception was thrown from `without_signal.cc`, line 6 (`throw "Something";`).

Now let's see what happens when an exception is thrown from a signal handler. Here's the source code.

    // with_signal.cc
    #include <gtkmm.h>

    bool throwSomething()
    {
      throw "Something";
      return true;
    }

    int main(int argc, char** argv)
    {
      Glib::signal_timeout().connect(sigc::ptr_fun(throwSomething), 500);
      auto app = Gtk::Application::create("org.gtkmm.with_signal");
      app->hold();
      return app->run();
    }

And here's an excerpt from a gdb session.

    > gdb with_signal
    (gdb) run
    (with_signal:2703): glibmm-ERROR **:
    unhandled exception (type unknown) in signal handler

    Program received signal SIGTRAP, Trace/breakpoint trap.
    (gdb) backtrace
    #2  0x0063c6ab in glibmm_unexpected_exception () at exceptionhandler.cc:77
    #3  Glib::exception_handlers_invoke () at exceptionhandler.cc:150
    #4  0x0063d370 in glibmm_source_callback (data=0x804d620) at main.cc:212
    #13 0x002e1b31 in Gtk::Application::run (this=0x804f300) at application.cc:178
    #14 0x08048ccc in main (argc=1, argv=0xbfffecd4) at with_signal.cc:16

The exception is caught in glibmm, and the program ends with a call to `g_error()`. Other exceptions may result in different behavior, but in any case the exception from a signal handler is caught in glibmm or gtkmm, and gdb can't see where it was thrown.

To see where the exception is thrown, you can use the gdb command `catch throw`.

    > gdb with_signal
    (gdb) catch throw
    Catchpoint 1 (throw)
    (gdb) run
    Catchpoint 1 (exception thrown), 0x00714ff0 in __cxa_throw ()
    (gdb) backtrace
    #0  0x00714ff0 in __cxa_throw () from /usr/lib/i386-linux-gnu/libstdc++.so.6
    #1  0x08048bd4 in throwSomething () at with_signal.cc:6
    (gdb) continue
    Continuing.
    (with_signal:2375): glibmm-ERROR **
    unhandled exception (type unknown) in signal handler

    Program received signal SIGTRAP, Trace/breakpoint trap.

If there are many caught exceptions before the interesting uncaught one, this method can be tedious. It can be automated with the following gdb commands.

    (gdb) catch throw
    (gdb) commands
    (gdb)   backtrace
    (gdb)   continue
    (gdb)   end
    (gdb) set pagination off
    (gdb) run

These commands will print a backtrace from each `throw` and continue. The backtrace from the last (or possibly the last but one) `throw` before the program stops, is the interesting one.

## Criando seus próprios sinais

Now that you've seen signals and signal handlers in gtkmm, you might like to use the same technique to allow interaction between your own classes. That's actually very simple by using the libsigc++ library directly.

This isn't purely a gtkmm or GUI issue. gtkmm uses libsigc++ to implement its proxy wrappers for the GTK signal system, but for new, non-GTK signals, you can create pure C++ signals, using the sigc::signal<> template.

For instance, to create a signal that sends 2 parameters, a bool and an int, just declare a sigc::signal, like so:

    sigc::signal<void(bool, int)> signal_something;

You could just declare that signal as a public member variable, but some people find that distasteful and prefer to make it available via an accessor method, like so:

    class Server
    {
    public:
      //signal accessor:
      using type_signal_something = sigc::signal<void(bool, int)>;
      type_signal_something signal_something();

    protected:
      type_signal_something m_signal_something;
    };

    Server::type_signal_something Server::signal_something()
    {
      return m_signal_something;
    }

You can then connect to the signal using the same syntax used when connecting to gtkmm signals. For instance,

    server.signal_something().connect(
      sigc::mem_fun(client, &Client::on_server_something) );

### Exemplo

This is a full working example that defines and uses custom signals.

Source Code

File: `client.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_CLIENT_H
    #define GTKMM_EXAMPLE_CLIENT_H

    #include <sigc++/sigc++.h>

    //Client must inherit from sigc::trackable.
    //because libsigc++ needs to keep track of the lifetime of signal handlers.
    class Client : public sigc::trackable
    {
    public:
      Client();
      virtual ~Client();

      //Signal handler:
      void on_server_something(bool a, int b);
    };

    #endif //GTKMM_EXAMPLE_CLIENT_H

File: `server.h` (For use with gtkmm 4)

    #ifndef GTKMM_EXAMPLE_SERVER_H
    #define GTKMM_EXAMPLE_SERVER_H

    #include <sigc++/sigc++.h>

    class Server
    {
    public:
      Server();
      virtual ~Server();

      void do_something();

      //signal accessor:
      using type_signal_something = sigc::signal<void(bool, int)>;
      type_signal_something signal_something();

    protected:
      type_signal_something m_signal_something;
    };

    #endif //GTKMM_EXAMPLE_SERVER_H

File: `client.cc` (For use with gtkmm 4)

    #include "client.h"
    #include <iostream>

    Client::Client()
    {
    }

    Client::~Client()
    {
    }

    void Client::on_server_something(bool a, int b)
    {
      std::cout << "Client::on_server_something() called with these parameters: "
          << a << ", " << b << std::endl;
    }

File: `main.cc` (For use with gtkmm 4)

    #include "server.h"
    #include "client.h"
    #include <iostream>

    int main(int, char**)
    {
      Server server;
      Client client;

      //Connect a Server signal to the signal handler in Client.
      server.signal_something().connect(sigc::mem_fun(client,
                  &Client::on_server_something) );

      std::cout << "Before Server::do_something()" << std::endl;

      //Tell the server to do something that will eventually cause it to emit the
      //"something" signal.
      server.do_something();    // Client::on_server_something() will run before
                                // Server::do_something() has completed.

      std::cout << "After Server::do_something()" << std::endl;

      return 0;
    }

File: `server.cc` (For use with gtkmm 4)

    #include "server.h"
    #include <iostream>

    Server::Server()
    {
    }

    Server::~Server()
    {
    }

    Server::type_signal_something Server::signal_something()
    {
      return m_signal_something;
    }

    void Server::do_something()
    {
      m_signal_something.emit(false, 5);
    }

## Comparison with other signalling systems

(An aside: GTK calls this scheme "signalling"; the sharp-eyed reader with GUI toolkit experience will note that this same design is often seen under the name of "broadcaster-listener" (e.g., in Metrowerks' PowerPlant framework for the Macintosh). It works in much the same way: one sets up `broadcasters`, and then connects `listeners` to them; the broadcaster keeps a list of the objects listening to it, and when someone gives the broadcaster a message, it calls all of its objects in its list with the message. In gtkmm, signal objects play the role of broadcasters, and slots play the role of listeners - sort of. More on this later.)

gtkmm signal handlers are strongly-typed, whereas GTK C code allows you to connect a callback with the wrong number and type of arguments, leading to a segfault at runtime. And, unlike Qt, gtkmm achieves this without modifying the C++ language.

Re. Overriding signal handlers: You can do this in the straight-C world of GTK too; that's what GTK's object system is for. But in GTK, you have to go through some complicated procedures to get object-oriented features like inheritance and overloading. In C++, it's simple, since those features are supported in the language itself; you can let the compiler do the dirty work.

This is one of the places where the beauty of C++ really comes out. One wouldn't think of subclassing a GTK widget simply to override its action method; it's just too much trouble. In GTK, you almost always use signals to get things done, unless you're writing a new widget. But because overriding methods is so easy in C++, it's entirely practical - and sensible - to subclass a button for that purpose.

## gtkmm e Win32

One of the major advantages of gtkmm is that it is crossplatform. gtkmm programs written on other platforms such as GNU/Linux can generally be transferred to Windows (and vice versa) with few modifications to the source.

gtkmm currently works with the MinGW/GCC compiler with a compiler version that supports C++17, such as gcc 7 or later. It also works with Microsoft Visual C++ 2017 15.7.x or later (including the freely available express/community editions) on the Windows platform. There is an installer available for gtkmm on Microsoft Windows, but as of this writing (December 2024) it only contains an installer for gtkmm2. Please be aware that although normally it is fine to mix builds done with Visual Studio 2017 and 2019, please do not do so when building gtkmm with its -mm dependencies.

There are README files, describing how to build gtkmm and its dependencies on Windows:

- libsigc++: MSVC_NMake/MSVC-Builds.md

- glibmm: README.win32.md

- cairomm: MSVC_NMake/MSVC-Builds.md

- pangomm: README.win32.md

- gtkmm: README.win32.md, MSVC_NMake/README

## Trabalhando com códigos fonte gtkmm

If you are interested in helping out with the development of gtkmm, or fixing a bug in gtkmm, you'll probably need to build the development version of gtkmm. However, you should not install a development version over your stable version. Instead, you should install it alongside your existing gtkmm installation, in a separate path.

The easiest way to do this is using jhbuild. jhbuild is a program that makes building GNOME software much easier by calculating dependencies and building things in the correct order. This section will give a brief explanation of how to set up jhbuild to build and install gtkmm from the source repository (git). For up-to-date information on jhbuild, please refer to the jhbuild manual.

Note that to build gtkmm from git, you'll often need to build many of its dependencies from git as well. jhbuild makes this easier than it would normally be, but it will take quite a while to build and install them all. You will probably encounter build problems, though these will usually be corrected quickly if you report them.

gnome-build-meta is an alternative to jhbuild. It is described at the Building system components wiki page, but here we concentrate on jhbuild.

### Configurando jhbuild

To set up jhbuild, follow the basic installation instructions from the jhbuild manual. After you have installed jhbuild, you should copy the sample jhbuild configuration file into your home directory by executing the following command from the jhbuild directory:

    $ cp examples/sample.jhbuildrc ~/.config/jhbuildrc

The gtkmm module is defined in the `gnome-suites-core-deps-latest.modules` moduleset. So edit your `jhbuildrc` file and set your moduleset setting like so:

    moduleset = 'gnome-suites-core-deps-latest'

After setting the correct moduleset, you need to tell jhbuild which module or modules to build. To build gtkmm and all of its dependencies, set `modules` like so:

    modules = [ 'gtkmm' ]

You can build several modules by setting the `modules` variable to a meta-package, e.g. `meta-gnome-core`, or listing more than one module name. The `modules` variable specifies which modules will be built when you don't explicitly specify anything on the command line. You can always build a different moduleset later by specifying it on the commandline (e.g. `jhbuild build gtkmm`).

Definindo um prefixo

By default, jhbuild's configuration is configured to install all software built with jhbuild under the `~/jhbuild/install` prefix. You can choose a different prefix, but it is recommended that you keep this prefix different from other software that you've installed (don't set it to `/usr`!) If you've followed the jhbuild instructions then this prefix belongs to your user, so you don't need to run jhbuild as `root`.

You should also set `buildroot` in `jhbuildrc`. jhbuild builds gtkmm and many of its dependencies with Meson. Meson does not allow building in the source tree. jhbuild's default action is to build in a `build` directory directly below the source root directory. Some modules have a `build` directory with files used when building with Autotools. Those files can be destroyed if you let jhbuild build in that directory.

When you downloaded jhbuild from the git repository, you got a number of `.modules` files, specifying dependencies between modules. By default jhbuild does not use the downloaded versions of these files, but reads the latest versions in the git repository. This is usually what you want. If you don't want it, use the `use_local_modulesets` variable in `jhbuildrc`.

### Installing and Using the git version of gtkmm

Once you've configured jhbuild as described above, building gtkmm should be relatively straightforward. The first time you run jhbuild, you should run the following sequence of commands to ensure that jhbuild has the required tools and verify that it is set up correctly:

    $ jhbuild bootstrap
    $ jhbuild sanitycheck

#### Installing gtkmm with jhbuild

If everything worked correctly, you should be able to build gtkmm and all of its dependencies from git by executing `jhbuild build` (or, if you didn't specify gtkmm in the `modules` variable, with the command `jhbuild build gtkmm`).

This command will build and install a series of modules and will probably take quite a long time the first time through. After the first time, however, it should go quite a bit faster since it only needs to rebuild files that changed since the last build. Alternatively, after you've built and installed gtkmm the first time, you can rebuild gtkmm by itself (without rebuilding all of its dependencies) with the command `jhbuild buildone gtkmm`.

#### Using the git version of gtkmm

After you've installed the git version of gtkmm, you're ready to start using and experimenting with it. In order to use the new version of gtkmm you've just installed, you need to set some environment variables so that your `configure` or `meson.build` script knows where to find the new libraries. Fortunately, jhbuild offers an easy solution to this problem. Executing the command `jhbuild shell` will start a new shell with all of the correct environment variables set. Now if you re-configure and build your project just as you usually do, it should link against the newly installed libraries. To return to your previous environment, simply exit the jhbuild shell.

Once you've built your software, you'll need to run your program within the jhbuild environment as well. To do this, you can again use the `jhbuild shell` command to start a new shell with the jhbuild environment set up. Alternatively, you can execute a one-off command in the jhbuild environment using the following command: `jhbuild run command-name`. In this case, the command will be run with the correct environment variables set, but will return to your previous environment after the program exits.

## Wrapping C Libraries with gmmproc

gtkmm uses the `gmmproc` tool to generate most of its source code, using .defs files that define the APIs of GObject-based libraries. So it's quite easy to create additional gtkmm-style wrappers of other glib/GObject-based libraries.

This involves a variety of tools, some of them crufty, but at least they work, and has been used successfully by several projects.

### Estrutura de construção

Generation of the source code for a gtkmm-style wrapper API requires use of tools such as `gmmproc` and `generate_wrap_init.pl`, which are included in glibmm. In theory you could write your own build files to use these appropriately, but a much better option is to make use of the build infrastructure provided by the mm-common module. To get started, it helps a lot to pick an existing binding module as an example to look at.

For instance, let's pretend that we are wrapping a C library called libsomething. It provides a GObject-based API with types named, for instance, SomeWidget and SomeStuff.

#### Copiando o esqueleto do projeto

Typically our wrapper library would be called libsomethingmm. We can start by copying the skeleton source tree from the mm-common module. Starting with mm-common 1.0.0 this skeleton application is built with the Meson build system.

      $ git clone https://gitlab.gnome.org/GNOME/mm-common.git
      $ cp -a mm-common/skeletonmm libsomethingmm

This provides a directory structure for the source .hg and .ccg files and the hand-written .h and .cc files, with `meson.build` files that can specify the various files in use, in terms of Meson variables. The directory structure usually looks like this, after we have renamed the directories appropriately:

- `libsomethingmm`: The top-level directory.

  - `libsomething`: Contains the main include file and the pkg-config .pc file.

    - `src`: Contains .hg and .ccg source files.

    - `libsomethingmm`: Contains hand-written .h and .cc files.

As well as renaming the directories, we should rename some of the source files. For instance:

    $ for f in $(find libsomethingmm -depth -name '*skeleton*'); do \
        d="${f%/*}"; b="${f##*/}"; mv "$f" "$d/${b//skeleton/libsomething}"; \
      done

A number of the skeleton files must still be filled in with project-specific content later.

Note that files ending in `.in` will be used to generate files with the same name but without the `.in` suffix, by replacing some variables with actual values during the configure stage.

Generated files are saved in the build tree, which is separated from the source tree when `meson` and `ninja` are used.

#### Modificando arquivos de construção

Now we edit the files to adapt them to our needs. You might prefer to use a multiple-file search-replace utility for this, such as `regexxer`. Note that nearly all of the files provided with the skeleton source tree contain placeholder text. Thus, the substitutions should be performed globally, and not be limited to the Meson files.

All mentions of `skeleton` should be replaced by the correct name of the C library you are wrapping, such as "something" or "libsomething". In the same manner, all instances of `SKELETON` should be replaced by "SOMETHING" or "LIBSOMETHING", and all occurrences of `Skeleton` changed to "Something".

Likewise, replace all instances of `Joe Hacker` by the name of the intended copyright holder, which is probably you. Do the same for the `joe@example.com` email address.

##### meson.build in the top-level directory

- It is common for binding modules to track the version number of the library they are wrapping. So, for instance, if the C library is at version 1.23.4, then the initial version of the binding module would be 1.23.0. However, avoid starting with an even minor version number as that usually indicates a stable release.

- In the `project()` function, change the license and the C++ version, if necessary.

- You probably need to add more required modules than glibmm and skeleton (libsomething).

##### Other meson.build files

Next we must adapt the other `meson.build` files:

- `skeleton/meson.build`: Perhaps not much to change here more than the global name substitutions.

- `skeleton/skeletonmm/meson.build`

  `defs_basefiles`

    If we have more .defs and docs.xml files, we add them here.

  `hg_ccg_basenames`

    We must mention all of our `.hg` and `.ccg` files here.

  `extra_cc_files, extra_h_files`

    Any additional hand-written `.h` and `.cc` source files go here.

##### Criação de arquivos .hg e .ccg

We should now create our first `.hg` and `.ccg` files, to wrap one of the objects in the C library. One pair of example source files already exists: `skeleton.ccg` and `skeleton.hg`. Create copies of these files as necessary.

In the .hg and .ccg files section you can learn about the syntax used in these files.

### Generating the .defs files

The `.defs` files are text files, in a lisp format, that describe the API of a C library, including its

- objects (GObjects, widgets, interfaces, boxed-types and plain structs)

- functions

- enums

- signals

- properties

- vfuncs

We split these `.defs` files into separate files. For instance, in the `gtk/src` directory of the gtkmm sources, you will find these files:

`gtk.defs`

  Includes the other files.

`gtk_methods.defs`

  Objects and functions.

`gtk_enums.defs`

  Enumerations.

`gtk_signals.defs`

  Signals and properties.

`gtk_vfuncs.defs`

  vfuncs (function pointer member fields in structs), written by hand.

The `skeletonmm/tools/generate_defs_and_docs.sh` script generates all `.defs` files and the `*_docs.xml` file, described in the Documentation section.

If the wrapped C library uses GObject-introspection and generates a GIR file, you can alternatively copy and adapt the `skeletonmm/tools/generate_from_gir.sh` script, which also generates all `.defs` files and the `*_docs.xml` file.

#### Generating .defs without a GIR file

##### Gerando o methods .defs

This `.defs` file describes objects and their functions. It is generated by the `h2def.py` script which you can find in glibmm's `tools/defs_gen` directory. For instance,

    $ ./h2def.py /usr/include/gtk-4.0/gtk/*.h > gtk_methods.defs

##### Gerando o enums .defs

This `.defs` file describes enum types and their possible values. It is generated by the `enumextract.py` script which you can also find in glibmm's `tools/defs_gen` directory. For instance,

    $ ./enumextract.py /usr/include/gtk-4.0/gtk/*.h > gtk_enums.defs

##### Generating the signals and properties .defs

This `.defs` file describes signals and properties. It is generated by the special `generate_extra_defs` utility that is in every wrapping project, such as `gtkmm/tools/extra_defs_gen/`. For instance

    $ cd tools/extra_defs_gen
    $ ./generate_extra_defs > gtk_signals.defs

You must edit the source code of your own `generate_extra_defs` tool in order to generate the `.defs` for the GObject C types that you wish to wrap. In the skeleton source tree, the source file is named `tools/extra_defs_gen/generate_defs_skeleton.cc`. If not done so already, the file should be renamed, with the basename of your new binding substituted for the `skeleton` placeholder. The `tools/extra_defs_gen/meson.build` file should also mention the new source filename.

Then edit the `.cc` file to specify the correct types. For instance, your `main()` function might look like this:

    #include <glibmm_generate_extra_defs/generate_extra_defs.h>
    #include <libsomething.h>
    #include <iostream>

    int main(int, char**)
    {
      something_init();

      std::cout << get_defs(SOME_TYPE_WIDGET)
                << get_defs(SOME_TYPE_STUFF);
      return 0;
    }

##### Escrevendo o vfuncs .defs

This `.defs` file describes virtual functions (vfuncs). It must be written by hand. There is the skeleton file `skeleton/src/skeleton_vfunc.defs` to start from. You can also look at gtkmm's `gtk/src/gtk_vfuncs.defs` file.

#### Generating .defs from a GIR file

Glibmm since version 2.88.1 contains the `mmgir` tool. This is a C++ program. To use it, build glibmm with `meson` with the `-Dbuild-mmgir=true` option.

`mmgir` can generate all the `.defs` files. For instance,

    $ ./mmgir --gir /usr/share/gir-1.0/Gtk-4.0.gir \
        --gir-search-dir /usr/share/gir-1.0 \
        --enum-defs gtk_enums.defs \
        --function-defs gtk_methods.defs \
        --signal-defs gtk_signals.defs \
        --vfunc-defs gtk_vfuncs.defs

### Os arquivos .hg e .ccg

The .hg and .ccg source files are very much like .h and .cc C++ source files, but they contain extra macros, such as `_CLASS_GOBJECT()` and `_WRAP_METHOD()`, from which `gmmproc` generates appropriate C++ source code, usually at the same position in the header. Any additional C++ source code will be copied verbatim into the corresponding .h or .cc file.

A .hg file will typically include some headers and then declare a class, using some macros to add API or behavior to this class. For instance, gtkmm's `button.hg` looks roughly like this:

    #include <gtkmm/widget.h>
    #include <gtkmm/actionable.h>
    _DEFS(gtkmm,gtk)
    _PINCLUDE(gtkmm/private/widget_p.h)

    namespace Gtk
    {

    class GTKMM_API Button
      : public Widget,
        public Actionable
    {
      _CLASS_GTKOBJECT(Button, GtkButton, GTK_BUTTON, Gtk::Widget, GtkWidget, , , GTKMM_API)
      _IMPLEMENTS_INTERFACE(Actionable)
    public:

      _CTOR_DEFAULT
      explicit Button(const Glib::ustring& label, bool mnemonic = false);

      _WRAP_METHOD(void set_label(const Glib::ustring& label), gtk_button_set_label)

      ...

      _WRAP_SIGNAL(void clicked(), "clicked")

      ...

      _WRAP_PROPERTY("label", Glib::ustring)
    };

    } // namespace Gtk

The macros in this example do the following:

`_DEFS()`

  Specifies the destination directory for generated sources, and the name of the main .defs file that `gmmproc` should parse.

`_PINCLUDE()`

  Tells `gmmproc` to include a header in the generated `private/button_p.h` file.

`_CLASS_GTKOBJECT()`

  Tells `gmmproc` to add some typedefs, constructors, and standard methods to this class, as appropriate when wrapping a widget.

`_IMPLEMENTS_INTERFACE()`

  Tells `gmmproc` to add initialization code for the interface.

`_CTOR_DEFAULT`

  Adds a default constructor.

`_WRAP_METHOD()`, `_WRAP_SIGNAL()`, and `_WRAP_PROPERTY()`

  Add methods to wrap parts of the C API.

The .h and .cc files will be generated from the .hg and .ccg files by processing them with `gmmproc` like so, though this happens automatically when using the above build structure:

    $ cd gtk/src
    $ /usr/lib/glibmm-2.68/proc/gmmproc -I ../../tools/m4 --defs . button . ./../gtkmm

Notice that we provided `gmmproc` with the path to the .m4 convert files, the path to the .defs file, the name of a .hg file, the source directory, and the destination directory.

You should avoid including the C header from your C++ header, to avoid polluting the global namespace, and to avoid exporting unnecessary public API. But you will need to include the necessary C headers from your .ccg file.

The macros are explained in more detail in the following sections.

#### Conversões m4

The macros that you use in the .hg and .ccg files often need to know how to convert a C++ type to a C type, or vice-versa. `gmmproc` takes this information from an .m4 file in your `tools/m4/` or `codegen/m4/` directory. This allows it to call a C function in the implementation of your C++ method, passing the appropriate parameters to that C function. For instance, this tells `gmmproc` how to convert a GtkTreeView pointer to a Gtk::TreeView pointer:

    _CONVERSION(`GtkTreeView*',`TreeView*',`Glib::wrap($3)')

`$3` will be replaced by the parameter name when this conversion is used by `gmmproc`.

Some extra macros make this easier and consistent. Look in gtkmm's .m4 files for examples. For instance:

    _CONVERSION(`PrintSettings&',`GtkPrintSettings*',__FR2P)
    _CONVERSION(`const PrintSettings&',`GtkPrintSettings*',__FCR2P)
    _CONVERSION(`const Glib::RefPtr<Printer>&',`GtkPrinter*',__CONVERT_REFPTR_TO_P($3))

#### Inicializações m4

Often when wrapping methods, it is desirable to store the return of the C function in what is called an output parameter. In this case, the C++ method returns void but an output parameter in which to store the value of the C function is included in the argument list of the C++ method. `gmmproc` allows such functionality, but appropriate initialization macros must be included to tell `gmmproc` how to initialize the C++ parameter from the return of the C function.

For example, if there was a C function that returned a GtkWidget* and for some reason, instead of having the C++ method also return the widget, it was desirable to have the C++ method place the widget in a specified output parameter, an initialization macro such as the following would be necessary:

    _INITIALIZATION(`Gtk::Widget&',`GtkWidget*',`$3 = Glib::wrap($4)')

`$3` will be replaced by the output parameter name of the C++ method and `$4` will be replaced by the return of the C function when this initialization is used by `gmmproc`. For convenience, `$1` will also be replaced by the C++ type without the ampersand (&) and `$2` will be replaced by the C type.

#### Macros de classes

The class macro declares the class itself and its relationship with the underlying C type. It generates some internal constructors, the member `gobject_`, typedefs, the `gobj()` accessors, type registration, and the `Glib::wrap()` method, among other things.

Other macros, such as `_WRAP_METHOD()` and `_WRAP_SIGNAL()` may only be used after a call to a `_CLASS_*` macro.

Most class macros take an optional argument, declaration prefix. It's typically used for a C preprocessor macro defined as `__declspec(dllexport)` or `__declspec(dllimport)` when building with MSVC on Windows, defined as an empty string otherwise.

##### _CLASS_GOBJECT

This macro declares a wrapper for a type that is derived from GObject, but whose wrapper is not derived from Gtk::Object.

`_CLASS_GOBJECT( C++ class, C class, C casting macro, C++ base class, C base class, real C class, real C base class, declaration prefix )`

real C class and real C base class are optional. They are seldom used. For instance, from `adjustment.hg`:

    _CLASS_GOBJECT(Adjustment, GtkAdjustment, GTK_ADJUSTMENT, Glib::Object, GObject, , , GTKMM_API)

##### _CLASS_GTKOBJECT

This macro declares a wrapper for a type whose wrapper is derived from Gtk::Object, such as a widget or dialog.

`_CLASS_GTKOBJECT( C++ class, C class, C casting macro, C++ base class, C base class, real C class, real C base class, declaration prefix )`

real C class and real C base class are optional. They are seldom used. For instance, from `button.hg`:

    _CLASS_GTKOBJECT(Button, GtkButton, GTK_BUTTON, Gtk::Widget, GtkWidget, , , GTKMM_API)

You will typically use this macro when the class already derives from Gtk::Object. For instance, you will use it when wrapping a GTK Widget, because Gtk::Widget derives from Gtk::Object.

You might also derive non-widget classes from Gtk::Object so they can be used without Glib::RefPtr. For instance, they could then be instantiated with `Gtk::make_managed()` or on the stack as a member variable. This is convenient, but you should use this only when you are sure that true reference-counting is not needed. We consider it useful for widgets.

##### _CLASS_BOXEDTYPE

This macro declares a wrapper for a non-GObject struct, registered with `g_boxed_type_register_static()`.

`_CLASS_BOXEDTYPE( C++ class, C class, new function, copy function, free function, declaration prefix )`

For instance, from Gdk::RGBA:

    _CLASS_BOXEDTYPE(RGBA, GdkRGBA, NONE, gdk_rgba_copy, gdk_rgba_free, GDKMM_API)

##### _CLASS_BOXEDTYPE_STATIC

This macro declares a wrapper for a simple assignable struct such as GdkRectangle. It is similar to `_CLASS_BOXEDTYPE`, but the C struct is not allocated dynamically.

`_CLASS_BOXEDTYPE_STATIC( C++ class, C class, declaration prefix )`

For instance, for Gdk::Rectangle:

    _CLASS_BOXEDTYPE_STATIC(Rectangle, GdkRectangle, GDKMM_API)

##### _CLASS_OPAQUE_COPYABLE

This macro declares a wrapper for an opaque struct that has copy and free functions. The new, copy and free functions will be used to instantiate the default constructor, copy constructor and destructor.

`_CLASS_OPAQUE_COPYABLE( C++ class, C class, new function, copy function, free function, declaration prefix )`

For instance, from Glib::VariantType:

    _CLASS_OPAQUE_COPYABLE(VariantType, GVariantType, NONE, g_variant_type_copy, g_variant_type_free, GLIBMM_API)

##### _CLASS_OPAQUE_REFCOUNTED

This macro declares a wrapper for a reference-counted opaque struct. The C++ wrapper cannot be directly instantiated and can only be used with Glib::RefPtr.

`_CLASS_OPAQUE_REFCOUNTED( C++ class, C class, new function, ref function, unref function, declaration prefix )`

For instance, for Gtk::CssSection:

    _CLASS_OPAQUE_REFCOUNTED(CssSection, GtkCssSection, NONE, gtk_css_section_ref, gtk_css_section_unref, GTKMM_API)

##### _CLASS_GENERIC

This macro can be used to wrap structs which don't fit into any specialized category.

`_CLASS_GENERIC( C++ class, C class )`

Note: No declaration prefix argument. For instance, for Gdk::TimeCoord:

    _CLASS_GENERIC(TimeCoord, GdkTimeCoord)

##### _CLASS_INTERFACE

This macro declares a wrapper for a type that is derived from GTypeInterface.

`_CLASS_INTERFACE( C++ class, C class, C casting macro, C interface struct, Base C++ class (optional), Base C class (optional), declaration prefix (optional) )`

For instance, from `celleditable.hg`:

    _CLASS_INTERFACE(CellEditable, GtkCellEditable, GTK_CELL_EDITABLE, GtkCellEditableIface, , , GTKMM_API)

Two extra optional parameters were once added, for the case that the interface derives from another interface, which was believed to be the case when the GInterface has another GInterface as a prerequisite. This is a misunderstanding, though. When GInterface A has GInterface B as a prerequisite, it means that every class that implements A shall also implement B. For instance, from `loadableicon.hg` in glibmm-2.4:

    _CLASS_INTERFACE(LoadableIcon, GLoadableIcon, G_LOADABLE_ICON, GLoadableIconIface, Icon, GIcon, GIOMM_API)

#### Contrutor de macros

The `_CTOR_DEFAULT()` and `_WRAP_CTOR()` macros add constructors, wrapping the specified `*_new()` C functions. These macros assume that the C object has properties with the same names as the function parameters, as is usually the case, so that it can supply the parameters directly to a `g_object_new()` call. These constructors never actually call the `*_new()` C functions, because gtkmm must actually instantiate derived GTypes, and the `*_new()` C functions are meant only as convenience functions for C programmers.

When using `_CLASS_GOBJECT()`, the constructors should be protected (rather than public) and each constructor should have a corresponding `_WRAP_CREATE()` in the public section. This prevents the class from being instantiated without using a RefPtr. For instance:

    class GTKMM_API TextMark : public Glib::Object
    {
      _CLASS_GOBJECT(TextMark, GtkTextMark, GTK_TEXT_MARK, Glib::Object, GObject, , , GTKMM_API)

    protected:
      _WRAP_CTOR(TextMark(const Glib::ustring& name, bool left_gravity = true), gtk_text_mark_new)

    public:
      _WRAP_CREATE(const Glib::ustring& name, bool left_gravity = true)

##### _CTOR_DEFAULT

This macro creates a default constructor with no arguments.

##### _WRAP_CTOR

This macro creates a constructor with arguments, equivalent to a `*_new()` C function. It won't actually call the `*_new()` function, but will simply create an equivalent constructor with the same argument types. It takes a C++ constructor signature, and a C function name.

It also takes an optional extra argument:

errthrow

  This tells `gmmproc` that the C `*_new()` has a final GError** parameter which should be ignored.

##### Hand-coding constructors

When a constructor must be partly hand written because, for instance, the `*_new()` C function's parameters do not correspond directly to object properties, or because the `*_new()` C function does more than call `g_object_new()`, the `_CONSTRUCT()` macro may be used in the .ccg file to save some work. The `_CONSTRUCT` macro takes a series of property names and values. For instance, from `button.ccg`:

    Button::Button(const Glib::ustring& label, bool mnemonic)
    :
      _CONSTRUCT("label", label.c_str(), "use_underline", gboolean(mnemonic))
    {}

#### Macros that suppress generation of some code

Some macros suppress the generation of some code when they are used after a `_CLASS_*` macro. Some suppress the definition in the generated .cc file, others suppress both the declaration in the .h file and the definition in the .cc file.

##### _CUSTOM_DEFAULT_CTOR

Suppresses declaration and definition of default constructor in `_CLASS_BOXEDTYPE`, `_CLASS_BOXEDTYPE_STATIC` and `_CLASS_OPAQUE_COPYABLE`.

##### _CUSTOM_CTOR_CAST

Suppresses declaration and definition of the constructor that takes a pointer to the wrapped C object in `_CLASS_BOXEDTYPE` and `_CLASS_BOXEDTYPE_STATIC`.

Suppresses definition of the constructor that takes a pointer to the wrapped C object in `_CLASS_INTERFACE` and `_CLASS_OPAQUE_COPYABLE`.

Suppresses definition of the constructor that takes a pointer to the wrapped C object and the constructor that takes construct_params in `_CLASS_GOBJECT` and `_CLASS_GTKOBJECT`.

##### _CUSTOM_DTOR

Suppresses definition of destructor in `_CLASS_GOBJECT` and `_CLASS_GTKOBJECT`.

##### _CUSTOM_MOVE_OPERATIONS

Suppresses declaration and definition of move constructor and move assignment operator in `_CLASS_GOBJECT` and `_CLASS_GTKOBJECT`.

For example:

    class Derived : public Glib::Object
    {
      _CLASS_GOBJECT(Derived, GDerived, G_DERIVED, Glib::Object, GObject)

      _CUSTOM_MOVE_OPERATIONS

    public:
      Derived(Derived&& src) noexcept;
      Derived& operator=(Derived&& src) noexcept;
      // ...
    };

##### _CUSTOM_WRAP_NEW

Suppresses definition of `Glib::wrap_new()` function in `_CLASS_GOBJECT`.

##### _CUSTOM_WRAP_FUNCTION

Suppresses definition of `Glib::wrap()` function in `_CLASS_GOBJECT` and `_CLASS_GTKOBJECT`.

##### _NO_WRAP_FUNCTION

Suppresses declaration and definition of `Glib::wrap()` function in `_CLASS_GOBJECT`, `_CLASS_BOXEDTYPE`, `_CLASS_BOXEDTYPE_STATIC`, `_CLASS_OPAQUE_COPYABLE`, `_CLASS_INTERFACE` and `_CLASS_GTKOBJECT`.

#### Métodos macros

##### _WRAP_METHOD

This macro generates the C++ method to wrap a C function.

`_WRAP_METHOD( C++ method signature, C function name)`

For instance, from `entry.hg`:

    _WRAP_METHOD(void set_text(const Glib::ustring& text), gtk_entry_set_text)

The C function (e.g. `gtk_entry_set_text`) is described more fully in the .defs file, and the `convert*.m4` files contain the necessary conversion from the C++ parameter type to the C parameter type. This macro also generates doxygen documentation comments based on the `*_docs.xml` and `*_docs_override.xml` files.

There are some optional extra arguments:

refreturn

  Do an extra `reference()` on the return value, in case the C function does not provide a reference.

errthrow ["<exceptions>"]

  Use the last GError** parameter of the C function to throw an exception. The optional "<exceptions>" is a comma-separated list of exceptions that can be thrown. It determines which @throws Doxygen commands are added to the documentation. Default value is Glib::Error. If you want a comma in the description of an exception, precede it by a backslash. Example: `errthrow "Glib::OptionError Hello\, world, Glib::ConvertError"`

deprecated ["<text>"]

  Puts the generated code in #ifdef blocks. Text about the deprecation can be specified as an optional parameter.

ignore_deprecations

  Puts the generated code in the .cc file in a G_GNUC_BEGIN_IGNORE_DEPRECATIONS / G_GNUC_END_IGNORE_DEPRECATIONS block. (Only in glibmm >= 2.70.1)

constversion

  Just call the non-const version of the same function, instead of generating almost duplicate code.

newin "<version>"

  Adds a @newin Doxygen command to the documentation, or replaces the @newin command generated from the C documentation.

ifdef <identifier>

  Puts the generated code in #ifdef blocks.

slot_name <parameter_name>

  Specifies the name of the slot parameter of the method, if it has one. This enables `gmmproc` to generate code to copy the slot and pass the copy on to the C function in its final `gpointer user_data` parameter. The `slot_callback` option must also be used to specify the name of the glue callback function to also pass on to the C function.

slot_callback <function_name>

  Used in conjunction with the `slot_name` option to specify the name of the glue callback function that handles extracting the slot and then calling it. The address of this callback is also passed on to the C function that the method wraps.

no_slot_copy

  Tells `gmmproc` not to pass a copy of the slot to the C function, if the method has one. Instead the slot itself is passed. The slot parameter name and the glue callback function must have been specified with the `slot_name` and `slot_callback` options respectively.

Selecting which C++ types should be used is also important when wrapping C API. Though it's usually obvious what C++ types should be used in the C++ method, here are some hints:

- Objects used via RefPtr: Pass the RefPtr as a const reference. For instance, `const Glib::RefPtr<Gtk::FileFilter>& filter`.

- Const Objects used via RefPtr: If the object should not be changed by the function, then make sure that the object is const, even if the RefPtr is already const. For instance, `const Glib::RefPtr<const Gtk::FileFilter>& filter`.

- Wrapping GList* and GSList* parameters: First, you need to discover what objects are contained in the list's data field for each item, usually by reading the documentation for the C function. The list can then be wrapped by a std::vector type. For instance, `std::vector<Glib::RefPtr<Gdk::Pixbuf>>`. You may need to define a Traits type to specify how the C and C++ types should be converted.

- Wrapping GList* and GSList* return types: You must discover whether the caller should free the list and whether it should release the items in the list, again by reading the documentation of the C function. With this information you can choose the ownership (none, shallow or deep) for the m4 conversion rule, which you should probably put directly into the .hg file because the ownership depends on the function rather than the type. For instance:

      #m4 _CONVERSION(`GSList*',`std::vector<Widget*>',`Glib::SListHandler<Widget*>::slist_to_vector($3, Glib::OWNERSHIP_SHALLOW)')

##### _WRAP_METHOD_DOCS_ONLY

This macro is like `_WRAP_METHOD()`, but it generates only the documentation for a C++ method that wraps a C function. Use this when you must hand-code the method, but you want to use the documentation that would be generated if the method was generated.

`_WRAP_METHOD_DOCS_ONLY(C function name)`

For instance, from `recentinfo.hg`:

    _WRAP_METHOD_DOCS_ONLY(gtk_recent_info_get_applications)

There are some optional extra arguments:

errthrow ["<exceptions>"]

  Excludes documentation of the last GError** parameter of the C function. The optional "<exceptions>" is a comma-separated list of exceptions that can be thrown. It determines which @throws Doxygen commands are added to the documentation. Default value is Glib::Error. If you want a comma in the description of an exception, precede it by a backslash. Example: `errthrow "Glib::OptionError Hello\, world, Glib::ConvertError"`

newin "<version>"

  Adds a @newin Doxygen command to the documentation, or replaces the @newin command generated from the C documentation.

voidreturn

  Don't include a @return Doxygen command in the documentation. Useful if the wrapped C function returns a value, but the corresponding C++ method returns void.

##### _IGNORE, _IGNORE_SIGNAL, _IGNORE_PROPERTY

`gmmproc` will warn you on stdout about functions, signals, properties and child properties that you have forgotten to wrap, helping to ensure that you are wrapping the complete API. But if you don't want to wrap some functions, signals, properties or child properties, or if you chose to hand-code some methods then you can use the _IGNORE(), _IGNORE_SIGNAL() or _IGNORE_PROPERTY() macro to make `gmmproc` stop complaining.

    _IGNORE(C function name 1, C function name 2, etc)
    _IGNORE_SIGNAL(C signal name 1, C signal name 2, etc)
    _IGNORE_PROPERTY(C property name 1, C property name 2, etc)

For instance, from `flowbox.hg`:

    _IGNORE(gtk_flow_box_set_filter_func, gtk_flow_box_set_sort_func)
    _IGNORE_SIGNAL(activate-cursor-child, toggle-cursor-child, move-cursor)

##### _WRAP_SIGNAL

This macro generates the C++ libsigc++-style signal to wrap a C GObject signal. It actually generates a public accessor method, such as `signal_clicked()`, which returns a proxy object. `gmmproc` uses the .defs file to discover the C parameter types and the .m4 convert files to discover appropriate type conversions.

`_WRAP_SIGNAL( C++ signal handler signature, C signal name)`

For instance, from `button.hg`:

    _WRAP_SIGNAL(void clicked(),"clicked")

Signals usually have function pointers in the GTK struct, with a corresponding enum value and a `g_signal_new()` in the .c file.

There are some optional extra arguments:

no_default_handler

  Do not generate an `on_something()` virtual method to allow easy overriding of the default signal handler. Use this when adding a signal with a default signal handler would break the ABI by increasing the size of the class's virtual function table, and when adding a signal without a public C default handler.

custom_default_handler

  Generate a declaration of the `on_something()` virtual method in the `.h` file, but do not generate a definition in the `.cc` file. Use this when you must generate the definition by hand.

custom_c_callback

  Do not generate a C callback function for the signal. Use this when you must generate the callback function by hand.

refreturn

  Do an extra `reference()` on the return value of the `on_something()` virtual method, in case the C function does not provide a reference.

deprecated ["<text>"]

  Puts the generated code in #ifdef blocks. Text about the deprecation can be specified as an optional parameter.

newin "<version>"

  Adds a @newin Doxygen command to the documentation, or replaces the @newin command generated from the C documentation.

ifdef <identifier>

  Puts the generated code in #ifdef blocks.

exception_handler <method_name>

  Allows to use custom exception handler instead of default one. Exception might be rethrown by user-defined handler, and it will be caught by default handler.

detail_name <parameter_name>

  Adds a const Glib::ustring& parameter to the signal_something() method. Use it, if the signal accepts a detailed signal name, i.e. if the underlying C code registers the signal with the `G_SIGNAL_DETAILED` flag.

two_signal_methods

  Used in conjunction with the `detail_name` option to generate two signal_something() methods, one without a parameter and one with a parameter without a default value. With only the `detail_name` option one method is generated, with a parameter with default value. Use the `two_signal_methods` option, if it's necessary in order to preserve ABI.

##### _WRAP_PROPERTY

This macro generates the C++ method to wrap a C GObject property. You must specify the property name and the wanted C++ type for the property. `gmmproc` uses the .defs file to discover the C type and the .m4 convert files to discover appropriate type conversions.

`_WRAP_PROPERTY(C property name, C++ type)`

For instance, from `button.hg`:

    _WRAP_PROPERTY("label", Glib::ustring)

There are some optional extra arguments:

deprecated ["<text>"]

  Puts the generated code in #ifdef blocks. Text about the deprecation can be specified as an optional parameter.

newin "<version>"

  Adds a @newin Doxygen command to the documentation, or replaces the @newin command generated from the C documentation.

##### _WRAP_VFUNC

This macro generates the C++ method to wrap a virtual C function.

`_WRAP_VFUNC( C++ method signature, C function name)`

For instance, from `widget.hg`:

    _WRAP_VFUNC(SizeRequestMode get_request_mode() const, get_request_mode)

The C function (e.g. `get_request_mode`) is described more fully in the `*_vfuncs.defs` file, and the `convert*.m4` files contain the necessary conversion from the C++ parameter type to the C parameter type. Conversions can also be written in the .hg file. Virtual functions often require special conversions that are best kept local to the .hg file where they are used.

There are some optional extra arguments:

refreturn

  Do an extra `reference()` on the return value of the `something_vfunc()` function, in case the virtual C function does not provide a reference.

refreturn_ctype

  Do an extra `reference()` on the return value of an overridden `something_vfunc()` function in the C callback function, in case the calling C function expects it to provide a reference.

keep_return

  Keep a copy of the return value in the C callback function, in case the calling C function does not expect to get its own reference.

errthrow

  Use the last GError** parameter of the C virtual function (if there is one) to throw an exception.

custom_vfunc

  Do not generate a definition of the vfunc in the `.cc` file. Use this when you must generate the vfunc by hand.

custom_vfunc_callback

  Do not generate a C callback function for the vfunc. Use this when you must generate the callback function by hand.

ifdef <identifier>

  Puts the generated code in #ifdef blocks.

slot_name <parameter_name>

  Specifies the name of the slot parameter of the method, if it has one. This enables `gmmproc` to generate code to copy the slot and pass the copy on to the C function in its final `gpointer user_data` parameter. The `slot_callback` option must also be used to specify the name of the glue callback function to also pass on to the C function.

slot_callback <function_name>

  Used in conjunction with the `slot_name` option to specify the name of the glue callback function that handles extracting the slot and then calling it. The address of this callback is also passed on to the C function that the method wraps.

no_slot_copy

  Tells `gmmproc` not to pass a copy of the slot to the C function, if the method has one. Instead the slot itself is passed. The slot parameter name and the glue callback function must have been specified with the `slot_name` and `slot_callback` options respectively.

return_value <value>

  Defines a non-default return value.

err_return_value <value>

  Defines a non-default return value, used only if the C++ `something_vfunc()` function throws an exception which is propagated to the C callback function. If return_value is specified, but err_return_value is not, then return_value is used also when an exception is propagated.

exception_handler <method_name>

  Allows to use custom exception handler instead of default one. Exception might be rethrown by user-defined handler, and it will be caught by default handler.

A rule to which there may be exceptions: If the virtual C function returns a pointer to an object derived from GObject, i.e. a reference-counted object, then the virtual C++ function shall return a Glib::RefPtr<> object. One of the extra arguments refreturn or refreturn_ctype is required.

#### Outros macros

##### _IMPLEMENTS_INTERFACE

Esta macro gera o código de inicialização para a interface.

`_IMPLEMENTS_INTERFACE(C++ interface name)`

For instance, from `grid.hg`:

    _IMPLEMENTS_INTERFACE(Orientable)

There is one optional extra argument:

ifdef <identifier>

  Puts the generated code in #ifdef blocks.

##### _WRAP_ENUM

This macro generates a C++ enum to wrap a C enum. You must specify the desired C++ name and the name of the underlying C enum.

For instance, from `enums.hg`:

    _WRAP_ENUM(Orientation, GtkOrientation, decl_prefix GTKMM_API)

There are some optional extra arguments:

NO_GTYPE

  Use this option, if the enum is not a GType. This is the case when there is no `*_get_type()` function for the C enum, but be careful that you don't just need to include an extra header for that function. You should also file a bug against the C API, because all enums should be registered as GTypes.

  If you specify `NO_GTYPE`, don't use that enum as the type in _WRAP_PROPERTY. It would cause a runtime error, when the generated property_*() method is called.

  For example, from `icontheme.hg`:

      _WRAP_ENUM(IconLookupFlags, GtkIconLookupFlags, NO_GTYPE, decl_prefix GTKMM_API)

gtype_func <function_name>

  Specifies the name of the `*_get_type()` function for the C enum. Use this parameter if `gmmproc` can't deduce the correct function name from the name of the C enum type.

  For example, from `dbusproxy.hg` in glibmm:

      _WRAP_ENUM(ProxyFlags, GDBusProxyFlags, gtype_func g_dbus_proxy_flags_get_type, decl_prefix GIOMM_API)

CONV_TO_INT

  "Convertible to int." Generates a plain enum (not an enum class) within a class. Such an enum is scoped like an enum class, but unlike an enum class, it can be implicitly converted to int.

  For example, from `dialog.hg`:

      _WRAP_ENUM(ResponseType, GtkResponseType, CONV_TO_INT, decl_prefix GTKMM_API)

s#<from>#<to>#

  Substitutes (part of) the name of one or more enum constants. You can add any number of substitutions.

  For example, from `toplevel.hg`:

      _WRAP_ENUM(FullscreenMode, GdkFullscreenMode,
        s#^CURRENT_MONITOR$#ON_CURRENT_MONITOR#, s#^ALL_MONITORS$#ON_ALL_MONITORS#,
        decl_prefix GDKMM_API)

decl_prefix <declaration_prefix>

  Typically used for a C preprocessor macro defined as `__declspec(dllexport)` or `__declspec(dllimport)` when building with MSVC on Windows, defined as an empty string otherwise.

deprecated ["<text>"]

  Puts the generated code in #ifdef blocks. Text about the deprecation can be specified as an optional parameter.

newin "<version>"

  Adds a @newin Doxygen command to the documentation, or replaces the @newin command generated from the C documentation.

##### _WRAP_ENUM_DOCS_ONLY

This macro just generates a Doxygen documentation block for the enum. This is useful for enums that can't be wrapped with `_WRAP_ENUM()` because they are complexly defined (maybe using C macros) but including the generated enum documentation is still desired. It is used with the same syntax as `_WRAP_ENUM()` and also processes the same options (though NO_GTYPE, gtype_func <function_name> and CONV_TO_INT are ignored because they make no difference when just generating the enum's documentation).

##### _WRAP_GERROR

This macro generates a C++ exception class, derived from Glib::Error, with a Code enum and a code() method. You must specify the desired C++ name, the name of the corresponding C enum, and the prefix for the C enum values.

This exception can then be thrown by methods which are generated from _WRAP_METHOD() with the errthrow option.

For instance, from `pixbuf.hg`:

    _WRAP_GERROR(PixbufError, GdkPixbufError, GDK_PIXBUF_ERROR, decl_prefix GDKMM_API)

_WRAP_GERROR() accepts the same optional arguments as _WRAP_ENUM() (though CONV_TO_INT is ignored because all exception class enums are plain enums within a class).

##### _MEMBER_GET / _MEMBER_SET

Use these macros if you're wrapping a simple struct or boxed type that provides direct access to its data members, to create getters and setters for the data members.

`_MEMBER_GET(C++ name, C name, C++ type, C type)`

`_MEMBER_SET(C++ name, C name, C++ type, C type)`

For example, in `rectangle.hg`:

    _MEMBER_GET(x, x, int, int)

##### _MEMBER_GET_PTR / _MEMBER_SET_PTR

Usa essas macros para automaticamente fornecer os método getters e setters para um dado membro que é um tipo ponteiro. Para a função getter, ele irá criar dois métodos, um const e um não-const.

`_MEMBER_GET_PTR(C++ name, C name, C++ type, C type)`

`_MEMBER_SET_PTR(C++ name, C name, C++ type, C type)`

For example, for Pango::Analysis in `item.hg`:

    // _MEMBER_GET_PTR(engine_lang, lang_engine, EngineLang*, PangoEngineLang*)
    // It's just a comment. It's difficult to find a real-world example.

##### _MEMBER_GET_GOBJECT / _MEMBER_SET_GOBJECT

Use these macros to provide getters and setters for a data member that is a GObject type that must be referenced before being returned.

`_MEMBER_GET_GOBJECT(C++ name, C name, C++ type, C type)`

`_MEMBER_SET_GOBJECT(C++ name, C name, C++ type, C type)`

For example, in Pangomm, `layoutline.hg`:

    _MEMBER_GET_GOBJECT(layout, layout, Pango::Layout, PangoLayout*)

#### gmmproc Parameter Processing

`gmmproc` allows processing the parameters in a method signature for the macros that process method signatures (like `_WRAP_METHOD()`, `_WRAP_CTOR()` and `_WRAP_CREATE()`) in a variety of ways:

##### Parameter Reordering

For all the macros that process method signatures, it is possible to specify a different order for the C++ parameters than the existing order in the C function, virtual function or signal. For example, say that the following C function were being wrapped as a C++ method for the Gtk::Widget class:

    void gtk_widget_set_device_events(GtkWidget* widget, GdkDevice* device,
      GdkEventMask events);

However, changing the order of the C++ method's two parameters is necessary. Something like the following would wrap the function as a C++ method with a different order for the two parameters:

    _WRAP_METHOD(void set_device_events(Gdk::EventMask events{events},
      const Glib::RefPtr<const Gdk::Device>& device{device}),
      gtk_widget_set_device_events)

The `{c_param_name}` following the method parameter names tells `gmmproc` to map the C++ parameter to the specified C parameter within the `{}`. Since the C++ parameter names correspond to the C ones, the above could be re-written as:

    _WRAP_METHOD(void set_device_events(Gdk::EventMask events{.},
      const Glib::RefPtr<const Gdk::Device>& device{.}),
      gtk_widget_set_device_events)

Please note that when reordering parameters for a `_WRAP_SIGNAL()` method signature, the C parameter names would always be `p0`, `p1`, etc. because the `generate_extra_defs` utility uses those parameter names no matter what the C API's parameter names may be. It's how the utility is written presently.

##### Optional Parameter Processing

For all macros processing method signatures except `_WRAP_SIGNAL()` and `_WRAP_VFUNC()` it is also possible to make the parameters optional so that extra C++ methods are generated without the specified optional parameter. For example, say that the following `*_new()` function were being wrapped as a constructor in the Gtk::ToolButton class:

    GtkToolItem* gtk_tool_button_new(GtkWidget* icon_widget, const gchar* label);

Also, say that the C API allowed NULL for the function's label parameter so that that parameter is optional. It would be possible to have `gmmproc` generate the original constructor (with all the parameters) along with an additional constructor without that optional parameter by appending a `{?}` to the parameter name like so:

    _WRAP_CTOR(ToolButton(Widget& icon_widget, const Glib::ustring& label{?}),
      gtk_tool_button_new)

In this case, two constructors would be generated: One with the optional parameter and one without it.

##### Output Parameter Processing

With `_WRAP_METHOD()` it is also possible for the return of the wrapped C function (if it has one) to be placed in an output parameter of the C++ method instead of having the C++ method also return a value like the C function does. To do that, simply include the output parameter in the C++ method parameter list appending a `{OUT}` to the output parameter name. For example, if `gtk_widget_get_request_mode()` is declared as the following:

    GtkSizeRequestMode gtk_widget_get_request_mode(GtkWidget* widget);

And having the C++ method set an output parameter is desired instead of returning a SizeRequestMode, something like the following could be used:

    _WRAP_METHOD(void get_request_mode(SizeRequestMode& mode{OUT}) const,
      gtk_widget_get_request_mode)

The `{OUT}` appended to the name of the mode output parameter tells `gmmproc` to place the return of the C function in that output parameter. In this case, however, a necessary initialization macro like the following would also have to be specified:

    _INITIALIZATION(`SizeRequestMode&',`GtkSizeRequestMode',`$3 = (SizeRequestMode)($4)')

Which could also be written as:

    _INITIALIZATION(`SizeRequestMode&',`GtkSizeRequestMode',`$3 = ($1)($4)')

`_WRAP_METHOD()` also supports setting C++ output parameters from C output parameters if the C function being wrapped has any. Suppose, for example, that we want to wrap the following C function that returns a value in its C output parameter out_mime_type:

    GInputStream* gdk_clipboard_read_finish(GdkClipboard* clipboard,
      GAsyncResult* result, const char** out_mime_type, GError** error)

To have `gmmproc` place the value returned in the C++ out_mime_type output parameter, something like the following `_WRAP_METHOD()` macro could be used:

    _WRAP_METHOD(Glib::RefPtr<Gio::InputStream> read_finish(
      const Glib::RefPtr<Gio::AsyncResult>& result,
      Glib::ustring& out_mime_type{>>}), gdk_clipboard_read_finish, errthrow)

The `{>>}` following the out_mime_type parameter name indicates that the C++ output parameter should be set from the value returned in the C parameter from the C function. `gmmproc` will generate a declaration of a temporary variable in which to store the value of the C output parameter and a statement that sets the C++ output parameter from the temporary variable. In this case it may be necessary to have an `_INITIALIZATION()` describing how to set a Glib::ustring& from a const char** such as the following:

    _INITIALIZATION(`Glib::ustring&',`const char*',`$3 = Glib::convert_const_gchar_ptr_to_ustring($4)')

##### String Parameter Processing

A string-valued input parameter in a C++ method is usually a const Glib::ustring& or a const std::string&. In C code it's a const gchar*. When an empty string is converted to const gchar*, it can be converted either to `nullptr` or to a pointer to an empty string (with c_str()). Some parameters in some C functions accept a `nullptr`, and interpret it in a special way. Other parameters must not be `nullptr`.

The default conversion in `_WRAP_METHOD()` and similar macros is

- for mandatory parameters (with or without default values): empty string to empty string,

- for optional parameters (with appended `{?}`): empty string to `nullptr`.

If the default conversion is not the best conversion, append `{NULL}` to a mandatory parameter or `{?!NULL}` to an optional parameter (`!NULL` = not `NULL`). If you append both a C parameter name and `NULL`, separate them with a space: `{c_param_name NULL}`.

#### Tipos básicos

Some of the basic types that are used in C APIs have better alternatives in C++. For example, there's no need for a gboolean type since C++ has bool. The following list shows some commonly-used types in C APIs and what you might convert them to in a C++ wrapper library.

Tipo C Tipo C++
- gboolean bool
- gint int
- guint guint
- gdouble double
- gunichar gunichar
- gchar*Glib::ustring (or std::string for filenames)

### Hand-coded source files

You might want to include additional source files that will not be generated by `gmmproc` from `.hg` and `.ccg` files. You can simply place these in your `libsomething/libsomethingmm` directory and mention them in the `meson.build` in the `extra_h_files` and `extra_cc_files` variables.

### Inicialização

Your library must be initialized before it can be used, to register the new types that it makes available. Also, the C library that you are wrapping might have its own initialization function that you should call. You can do this in an `init()` function that you can place in hand-coded `init.h` and `init.cc` files. This function should initialize your dependencies (such as the C function, and gtkmm) and call your generated `wrap_init()` function. For instance:

    void init()
    {
      Gtk::init_gtkmm_internals(); //Sets up the g type system and the Glib::wrap() table.
      wrap_init(); //Tells the Glib::wrap() table about the libsomethingmm classes.
    }

The implementation of the `wrap_init()` method in `wrap_init.cc` is generated by `generate_wrap_init.pl`, but the declaration in `wrap_init.h` is hand-coded, so you will need to adjust `wrap_init.h` so that the `wrap_init()` function appears in the correct C++ namespace.

### Problems in the C API

You are likely to encounter some problems in the library that you are wrapping, particularly if it is a new project. Here are some common problems, with solutions.

#### Unable to predeclare structs

By convention, structs are declared in glib/GTK-style headers like so:

    typedef struct _ExampleWidget ExampleWidget;

    struct _ExampleWidget
    {
      ...
    };

The extra typedef allows the struct to be used in a header without including its full definition, simply by predeclaring it, by repeating that typedef. This means that you don't have to include the C library's header in your C++ header, thus keeping it out of your public API. `gmmproc` assumes that this technique was used, so you will see compiler errors if that is not the case.

This compiler error might look like this:

    example-widget.h:56: error: using typedef-name 'ExampleWidget' after 'struct'
    ../../libexample/libexamplemm/example-widget.h:34: error: 'ExampleWidget' has a previous declaration here
    make[4]: *** [example-widget.lo] Error 1

or this:

    example-widget.h:60: error: '_ExampleWidget ExampleWidget' redeclared as different kind of symbol
    ../../libexample/libexamplemm/example-widget.h:34: error: previous declaration of 'typedef struct _ExampleWidget ExampleWidget'

This is easy to correct in the C library, so do send a patch to the relevant maintainer.

#### Falta de propriedades

By convention, glib/GTK-style objects have `*_new()` functions, such as `example_widget_new()` that do nothing more than call `g_object_new()` and return the result. The input parameters are supplied to `g_object_new()` along with the names of the properties for which they are values. For instance,

    GtkWidget* example_widget_new(int something, const char* thing)
    {
            return g_object_new (EXAMPLE_TYPE_WIDGET, "something", something, "thing", thing, NULL);
    }

This allows language bindings to implement their own equivalents (such as C++ constructors), without using the `*_new()` function. This is often necessary so that they can actually instantiate a derived GType, to add their own hooks for signal handlers and vfuncs.

At the least, the `_new()` function should not use any private API (functions that are only in a .c file). Even when there are no functions, we can sometimes reimplement 2 or 3 lines of code in a `_new()` function as long as those lines of code use API that is available to us.

Another workaround is to add a `*_construct()` function that the C++ constructor can call after instantiating its own type. For instance,

    GtkWidget* example_widget_new(int something, const char* thing)
    {
            ExampleWidget* widget;
            widget = g_object_new (EXAMPLE_TYPE_WIDGET, NULL);
            example_widget_construct(widget, "something", something, "thing", thing);
    }

    void example_widget_construct(ExampleWidget* widget, int something, const char* thing)
    {
            //Do stuff that uses private API:
            widget->priv->thing = thing;
            do_something(something);
    }

Adding properties, and ensuring that they interact properly with each other, is relatively difficult to correct in the C library, but it is possible, so do file a bug and try to send a patch to the relevant maintainer.

### Documentação

In general, gtkmm-style projects use Doxygen, which reads specially formatted C++ comments and generates HTML documentation. You may write these doxygen comments directly in the header files.

#### Reutilizando documentação C

You might wish to reuse documentation that exists for the C library that you are wrapping. GTK-style C libraries typically use gtk-doc or gi-docgen and therefore have source code comments formatted for gtk-doc or gi-docgen and some extra documentation in .sgml and .xml files. The docextract_to_xml.py script, from glibmm's `tools/defs_gen` directory, can read these files and generate an .xml file that `gmmproc` can use to generate doxygen comments. `gmmproc` will even try to transform the documentation to make it more appropriate for a C++ API.

Por exemplo,

    ./docextract_to_xml.py -s ~/checkout/gnome/gtk/gtk/ > gtk_docs.xml

Because this automatic transformation is not always appropriate, you might want to provide hand-written text for a particular method. You can do this by copying the XML node for the function from your `something_docs.xml` file to the `something_docs_override.xml` file and changing the contents. Alternatively you can write your own documentation in the `.hg` file.

#### Documentação da estrutura de construção

If you copied the skeleton source tree in mm-common and substituted the placeholder text, then you will already have suitable `meson.build` and `Doxyfile.in` files in the `doc/reference/` directory. You probably need to modify the `tag_file_modules` variable in `meson.build`, though. With the mm-common build setup, the list of Doxygen input files is not defined in the Doxygen configuration file, but passed along from `meson/ninja` to the standard input of `doxygen`.

## GNU Free Documentation License

Copyright (C) 2000, 2001, 2002 Free Software Foundation, https://fsf.org/. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

#### 0. PREAMBLE

The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

#### 1. APPLICABILITY AND DEFINITIONS

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#### 2. VERBATIM COPYING

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

#### 3. COPYING IN QUANTITY

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#### 4. MODIFICATIONS

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.

2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.

3. State on the Title page the name of the publisher of the Modified Version, as the publisher.

4. Preserve all the copyright notices of the Document.

5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.

6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.

7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.

8. Include an unaltered copy of this License.

9. Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.

10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.

11. For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.

12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.

13. Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version.

14. Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section.

15. Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

#### 5. COMBINING DOCUMENTS

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements".

#### 6. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

#### 7. AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

#### 8. TRANSLATION

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

#### 9. TERMINATION

You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

#### 10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See https://www.gnu.org/licenses/.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

#### ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

> Copyright (C) YEAR YOUR NAME.

> Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with...Texts." line with this:

> with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.