The QSignalSpy class enables introspection of signal emission. More...
| Header: | #include <QSignalSpy> |
| CMake: | find_package(Qt6 REQUIRED COMPONENTS Test) target_link_libraries(mytarget PRIVATE Qt6::Test) |
| qmake: | QT += testlib |
| Inherits: | QObject and QList |
| QSignalSpy(const QObject *obj, const QMetaMethod &signal) | |
| QSignalSpy(const QObject *object, PointerToMemberFunction signal) | |
| QSignalSpy(const QObject *object, const char *signal) | |
| bool | isValid() const |
| QByteArray | signal() const |
| bool | wait(int timeout = 5000) |
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).typeId() == QMetaType::Int); QVERIFY(arguments.at(1).typeId() == QMetaType::QString); QVERIFY(arguments.at(2).typeId() == QMetaType::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));
The QSignalSpy class provides an elegant mechanism for capturing the list of signals emitted by an object. However, you should verify its validity after construction. The constructor does a number of sanity checks, such as
verifying that the signal to be spied upon actually exists. To make the diagnosis of test failures easier, the results of these checks should be checked by calling QVERIFY(spy.isValid()) before proceeding further
with a test.
See also QVERIFY().
[since 5.14] QSignalSpy::QSignalSpy(const QObject *obj, const QMetaMethod &signal)Constructs a new QSignalSpy that listens for emissions of the signal from the QObject obj. If QSignalSpy is not able to listen for a valid signal (for example, because obj
is nullptr or signal does not denote a valid signal of obj), an explanatory warning message will be output using qWarning() and subsequent calls to
isValid() will return false.
This constructor is convenient to use when Qt's meta-object system is heavily used in a test.
Basic usage example:
QObject object; auto mo = object.metaObject(); auto signalIndex = mo->indexOfSignal("objectNameChanged(QString)"); auto signal = mo->method(signalIndex); QSignalSpy spy(&object, signal); object.setObjectName("A new object name"); QCOMPARE(spy.count(), 1);
Imagine we need to check whether all properties of the QWindow class that represent minimum and maximum dimensions are properly writable. The following example demonstrates one of the approaches:
void tst_QWindow::writeMinMaxDimensionalProps_data() QTest::addColumn<int>("propertyIndex"); // Collect all relevant properties static const auto mo = QWindow::staticMetaObject; for (int i = mo.propertyOffset(); i < mo.propertyCount(); ++i) { auto property = mo.property(i); // ...that have type int if (property.type() == QVariant::Int) { static const QRegularExpression re("^minimum|maximum"); const auto name = property.name(); // ...and start with "minimum" or "maximum" if (re.match(name).hasMatch()) { QTest::addRow("%s", name) << i; } } } } void tst_QWindow::writeMinMaxDimensionalProps() { QFETCH(int, propertyIndex); auto property = QWindow::staticMetaObject.property(propertyIndex); QVERIFY(property.isWritable()); QVERIFY(property.hasNotifySignal()); QWindow window; QSignalSpy spy(&window, property.notifySignal()); QVERIFY(property.write(&window, 42)); QCOMPARE(spy.count(), 1); }
This function was introduced in Qt 5.14.
[since 5.4] template <typename PointerToMemberFunction> 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 nullptr 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.
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 nullptr 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)));
Returns true if the signal spy listens to a valid signal, otherwise false.
Returns the normalized signal the spy is currently listening to.
[since 5.0] 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.
