SignalSpy QML Type | Qt Quick Test | Qt 6.10.3
Description: Enables introspection of signal emission.

- Qt 6.10
- Qt Quick Test
- QML Types
- SignalSpy
- Qt 6.10.3 Reference Documentation

# SignalSpy QML Type

Enables introspection of signal emission. More...

Import Statement: | `import QtTest`
Inherits: | Item

- List of all members, including inherited members

## Properties

- count : int
- signalArguments : list
- signalName : string
- target : object
- valid : bool

## Methods

- clear()
- wait(timeout)

## Detailed Description

In the following example, a SignalSpy is installed to watch the "clicked" signal on a user-defined Button type. When the signal is emitted, the count property on the spy will be increased.

     Button {
         id: button
         SignalSpy {
             id: spy
             target: button
             signalName: "clicked"
         }
         TestCase {
             name: "ButtonClick"
             function test_click() {
                 compare(spy.count, 0)
                 button.clicked();
                 compare(spy.count, 1)
             }
         }
     }

The above style of test is suitable for signals that are emitted synchronously. For asynchronous signals, the wait() method can be used to block the test until the signal occurs (or a timeout expires).

See also TestCase and Qt Quick Test.

## Property Documentation

count : int `[read-only]`

This property defines the number of times that signalName has been emitted from target since the last call to clear().

See also target, signalName, and clear().

signalArguments : list `[read-only]`

This property holds a list of emitted signal arguments. Each emission of the signal will append one item to the list, containing the arguments of the signal. When connecting to a new target or new signalName or calling the clear() method, the signalArguments will be reset to empty.

See also signalName and clear().

signalName : string

This property defines the name of the signal on target to listen for.

See also target and count.

target : object

This property defines the target object that will be used to listen for emissions of the signalName signal.

See also signalName and count.

valid : bool `[read-only]`

This property defines the current signal connection status. It will be true when the signalName of the target is connected successfully, otherwise it will be false.

See also count, target, signalName, and clear().

## Method Documentation

clear()

Clears count to `0` and signalArguments to empty. Does not affect valid.

See also count and wait().

wait(timeout = 5000)

Waits for the signal signalName on target to be emitted, for up to timeout milliseconds. The test case will fail if the signal is not emitted.

     SignalSpy {
         id: spy
         target: button
         signalName: "clicked"
     }

     function test_async_click() {
         ...
         // do something that will cause clicked() to be emitted
         ...
         spy.wait()
         compare(spy.count, 1)
     }

There are two possible scenarios: the signal has already been emitted when wait() is called, or the signal has not yet been emitted. The wait() function handles the first scenario by immediately returning if the signal has already occurred.

The clear() method can be used to discard information about signals that have already occurred to synchronize wait() with future signal emissions.

See also clear() and TestCase::tryCompare().