QSignalSpy Class

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

Header: #include <QSignalSpy>
qmake: QT += testlib
Inherits: QObject and QList
typedef QObjectList

Macros

Additional Inherited Members

  • 1 property inherited from QObject
  • 16 public functions inherited from QObject
  • 1 public slot inherited from QObject
  • 1 signal inherited from QObject
  • 5 static public members inherited from QObject
  • 8 protected functions inherited from QObject

Detailed Description

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));