QMetaMethod¶

PyQt5.QtCore.QMetaMethod

Description¶

The QMetaMethod class provides meta-data about a member function.

A QMetaMethod has a methodType(), a methodSignature(), a list of parameterTypes() and parameterNames(), a return typeName(), a tag(), and an access() specifier. You can use invoke() to invoke the method on an arbitrary QObject.

Enums¶

Access

This enum describes the access level of a method, following the conventions used in C++.

Member	Value	Description
Private	TODO	TODO
Protected	TODO	TODO
Public	TODO	TODO

MethodType

Member	Value	Description
Constructor	3	The function is a constructor.
Method	0	The function is a plain member function.
Signal	1	The function is a signal.
Slot	2	The function is a slot.

Methods¶

__init__(): TODO

__init__(QMetaMethod): TODO

access() → Access

Returns the access specification of this method (private, protected, or public).

Note: Signals are always public, but you should regard that as an implementation detail. It is almost always a bad idea to emit a signal from outside its class.

See also

methodType().

__eq__(QMetaMethod) → bool: TODO

invoke(QObject, value0: QGenericArgument = QGenericArgument(0,0), value1: QGenericArgument = QGenericArgument(0,0), value2: QGenericArgument = QGenericArgument(0,0), value3: QGenericArgument = QGenericArgument(0,0), value4: QGenericArgument = QGenericArgument(0,0), value5: QGenericArgument = QGenericArgument(0,0), value6: QGenericArgument = QGenericArgument(0,0), value7: QGenericArgument = QGenericArgument(0,0), value8: QGenericArgument = QGenericArgument(0,0), value9: QGenericArgument = QGenericArgument(0,0)) → object: TODO

invoke(QObject, QGenericReturnArgument, value0: QGenericArgument = QGenericArgument(0,0), value1: QGenericArgument = QGenericArgument(0,0), value2: QGenericArgument = QGenericArgument(0,0), value3: QGenericArgument = QGenericArgument(0,0), value4: QGenericArgument = QGenericArgument(0,0), value5: QGenericArgument = QGenericArgument(0,0), value6: QGenericArgument = QGenericArgument(0,0), value7: QGenericArgument = QGenericArgument(0,0), value8: QGenericArgument = QGenericArgument(0,0), value9: QGenericArgument = QGenericArgument(0,0)) → object: TODO

invoke(QObject, ConnectionType, value0: QGenericArgument = QGenericArgument(0,0), value1: QGenericArgument = QGenericArgument(0,0), value2: QGenericArgument = QGenericArgument(0,0), value3: QGenericArgument = QGenericArgument(0,0), value4: QGenericArgument = QGenericArgument(0,0), value5: QGenericArgument = QGenericArgument(0,0), value6: QGenericArgument = QGenericArgument(0,0), value7: QGenericArgument = QGenericArgument(0,0), value8: QGenericArgument = QGenericArgument(0,0), value9: QGenericArgument = QGenericArgument(0,0)) → object: TODO

invoke(QObject, ConnectionType, QGenericReturnArgument, value0: QGenericArgument = QGenericArgument(0,0), value1: QGenericArgument = QGenericArgument(0,0), value2: QGenericArgument = QGenericArgument(0,0), value3: QGenericArgument = QGenericArgument(0,0), value4: QGenericArgument = QGenericArgument(0,0), value5: QGenericArgument = QGenericArgument(0,0), value6: QGenericArgument = QGenericArgument(0,0), value7: QGenericArgument = QGenericArgument(0,0), value8: QGenericArgument = QGenericArgument(0,0), value9: QGenericArgument = QGenericArgument(0,0)) → object

Invokes this method on the object object. Returns true if the member could be invoked. Returns false if there is no such member or the parameters did not match.

The invocation can be either synchronous or asynchronous, depending on the connectionType:

If connectionType is DirectConnection, the member will be invoked immediately.
If connectionType is QueuedConnection, a QEvent will be posted and the member is invoked as soon as the application enters the main event loop.
If connectionType is AutoConnection, the member is invoked synchronously if object lives in the same thread as the caller; otherwise it will invoke the member asynchronously.

The return value of this method call is placed in returnValue. If the invocation is asynchronous, the return value cannot be evaluated. You can pass up to ten arguments (val0, val1, val2, val3, val4, val5, val6, val7, val8, and val9) to this method call.

QGenericArgument and QGenericReturnArgument are internal helper classes. Because signals and slots can be dynamically invoked, you must enclose the arguments using the Q_ARG() and Q_RETURN_ARG() macros. Q_ARG() takes a type name and a const reference of that type; Q_RETURN_ARG() takes a type name and a non-const reference.

To asynchronously invoke the animateClick() slot on a QPushButton:

# int methodIndex = pushButton->metaObject()->indexOfMethod("animateClick()");
# QMetaMethod method = metaObject->method(methodIndex);
# method.invoke(pushButton, Qt::QueuedConnection);

With asynchronous method invocations, the parameters must be of types that are known to Qt’s meta-object system, because Qt needs to copy the arguments to store them in an event behind the scenes. If you try to use a queued connection and get the error message

# QMetaMethod::invoke: Unable to handle unregistered datatype 'MyType'

call qRegisterMetaType() to register the data type before you call .

To synchronously invoke the compute(QString, int, double) slot on some arbitrary object obj retrieve its return value:

# QString retVal;
# QByteArray normalizedSignature = QMetaObject::normalizedSignature("compute(QString, int, double)");
# int methodIndex = obj->metaObject()->indexOfMethod(normalizedSignature);
# QMetaMethod method = obj->metaObject()->method(methodIndex);
# method.invoke(obj,
#               Qt::DirectConnection,
#               Q_RETURN_ARG(QString, retVal),
#               Q_ARG(QString, "sqrt"),
#               Q_ARG(int, 42),
#               Q_ARG(double, 9.7));

normalizedSignature() is used here to ensure that the format of the signature is what expects. E.g. extra whitespace is removed.

If the “compute” slot does not take exactly one QString, one int and one double in the specified order, the call will fail.

Warning: this method will not test the validity of the arguments: object must be an instance of the class of the QMetaObject of which this QMetaMethod has been constructed with. The arguments must have the same type as the ones expected by the method, else, the behaviour is undefined.

See also

Q_ARG(), Q_RETURN_ARG(), qRegisterMetaType(), invokeMethod().

isValid() → bool: TODO

methodIndex() → int: Returns this method’s index.

methodSignature() → QByteArray: TODO

methodType() → MethodType: Returns the type of this method (signal, slot, or method).

See also

access().

name() → QByteArray: TODO

__ne__(QMetaMethod) → bool: TODO

parameterCount() → int: TODO

parameterNames() → List[QByteArray]: Returns a list of parameter names.

See also

parameterTypes().

parameterType(int) → int: TODO

parameterTypes() → List[QByteArray]: Returns a list of parameter types.

See also

parameterNames().

returnType() → int: TODO

tag() → str

Returns the tag associated with this method.

Tags are special macros recognized by moc that make it possible to add extra information about a method.

Tag information can be added in the following way in the function declaration:

#     // In the class MainWindow declaration
#     #ifndef Q_MOC_RUN
#     // define the tag text as empty, so the compiler doesn't see it
#     #  define MY_CUSTOM_TAG
#     #endif
#     ...
#     private slots:
#         MY_CUSTOM_TAG void testFunc();

and the information can be accessed by using:

#     MainWindow win;
#     win.show();

#     int functionIndex = win.metaObject()->indexOfSlot("testFunc()");
#     QMetaMethod mm = win.metaObject()->method(functionIndex);
#     qDebug() << mm.tag(); // prints MY_CUSTOM_TAG

For the moment, moc will extract and record all tags, but it will not handle any of them specially. You can use the tags to annotate your methods differently, and treat them according to the specific needs of your application.

Note: Since Qt 5.0, moc expands preprocessor macros, so it is necessary to surround the definition with #ifndef Q_MOC_RUN, as shown in the example above. This was not required in Qt 4. The code as shown above works with Qt 4 too.

typeName() → str: Returns the return type name of this method.

See also

type(), returnType().