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QSignalSpy Class

The QSignalSpy class enables introspection of signal emission. More...

Header: #include <QSignalSpy>
qmake: QT += testlib
Inherits: QObject

Public Functions

QSignalSpy(const QObject *object, const char *signal)
QSignalSpy(const QObject *object, PointerToMemberFunction signal)
bool isValid() const
QByteArray signal() const
bool wait(int timeout = 5000)
  • 31 public functions inherited from QObject

Additional Inherited Members

  • 1 property inherited from QObject
  • 1 public slot inherited from QObject
  • 2 signals inherited from QObject
  • 9 static public members inherited from QObject
  • 9 protected functions inherited from QObject

Detailed Description

The QSignalSpy class enables introspection of signal emission.

QSignalSpy can connect to any signal of any object and records its emission. QSignalSpy itself is a list of QVariant lists. Each emission of the signal will append one item to the list, containing the arguments of the signal.

The following example records all signal emissions for the clicked() signal of a QCheckBox:

QCheckBox *box = ...;
QSignalSpy spy(box, SIGNAL(clicked(bool)));

// do something that triggers the signal
box->animateClick();

QCOMPARE(spy.count(), 1); // make sure the signal was emitted exactly one time
QList<QVariant> arguments = spy.takeFirst(); // take the first signal

QVERIFY(arguments.at(0).toBool() == true); // verify the first argument

spy.takeFirst() returns the arguments for the first emitted signal, as a list of QVariant objects. The clicked() signal has a single bool argument, which is stored as the first entry in the list of arguments.

The example below catches a signal from a custom object:

QSignalSpy spy(myCustomObject, SIGNAL(mySignal(int,QString,double)));

myCustomObject->doSomething(); // trigger emission of the signal

QList<QVariant> arguments = spy.takeFirst();
QVERIFY(arguments.at(0).type() == QVariant::Int);
QVERIFY(arguments.at(1).type() == QVariant::String);
QVERIFY(arguments.at(2).type() == QVariant::double);

Note: Non-standard data types need to be registered, using the qRegisterMetaType() function, before you can create a QSignalSpy. For example:

qRegisterMetaType<SomeStruct>();
QSignalSpy spy(&model, SIGNAL(whatever(SomeStruct)));

To retrieve the instance, you can use qvariant_cast:

// get the first argument from the first received signal:
SomeStruct result = qvariant_cast<SomeStruct>(spy.at(0).at(0));

Member Function Documentation

QSignalSpy::QSignalSpy(const QObject *object, const char *signal)

Constructs a new QSignalSpy that listens for emissions of the signal from the QObject object. If QSignalSpy is not able to listen for a valid signal (for example, because object is null or signal does not denote a valid signal of object), an explanatory warning message will be output using qWarning() and subsequent calls to isValid() will return false.

Example:

QSignalSpy spy(myPushButton, SIGNAL(clicked(bool)));

QSignalSpy::QSignalSpy(const QObject *object, PointerToMemberFunction signal)

Constructs a new QSignalSpy that listens for emissions of the signal from the QObject object. If QSignalSpy is not able to listen for a valid signal (for example, because object is null or signal does not denote a valid signal of object), an explanatory warning message will be output using qWarning() and subsequent calls to isValid() will return false.

Example:

QSignalSpy spy(myPushButton, &QPushButton::clicked);

This function was introduced in Qt 5.4.

bool QSignalSpy::isValid() const

Returns true if the signal spy listens to a valid signal, otherwise false.

QByteArray QSignalSpy::signal() const

Returns the normalized signal the spy is currently listening to.

bool QSignalSpy::wait(int timeout = 5000)

Starts an event loop that runs until the given signal is received. Optionally the event loop can return earlier on a timeout (in milliseconds).

Returns true if the signal was emitted at least once in timeout milliseconds, otherwise returns false.

Example:

QVERIFY(spy.wait(1000));

This function was introduced in Qt 5.0.

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