QMetaMethod Class

See also QMetaObject, QMetaEnum, QMetaProperty, Qt's Property System

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

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

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Returns the meta-method that corresponds to the given signal, or an invalid QMetaMethod if signal is not a signal of the class.

Example:

QMetaMethod destroyedSignal = QMetaMethod::fromSignal(&QObject::destroyed);

This function was introduced in Qt 5.0.

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 Qt::DirectConnection, the member will be invoked immediately.

• If connectionType is Qt::QueuedConnection, a QEvent will be posted and the member is invoked as soon as the application enters the main event loop.

• If connectionType is Qt::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 QMetaMethod::invoke().

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));

QMetaObject::normalizedSignature() is used here to ensure that the format of the signature is what invoke() 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.

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This function overloads invoke().

This overload always invokes this method using the connection type Qt::AutoConnection.

This function overloads invoke().

This overload can be used if the return value of the member is of no interest.

This function overloads invoke().

This overload invokes this method using the connection type Qt::AutoConnection and ignores return values.

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

The pointer gadget must point to an instance of the gadget class.

The invocation is always synchronous.

The return value of this method call is placed in returnValue. You can pass up to ten arguments (val0, val1, val2, val3, val4, val5, val6, val7, val8, and val9) to this method call.

This function was introduced in Qt 5.5.

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This is an overloaded function.

This overload invokes this method for a gadget and ignores return values.

This function was introduced in Qt 5.5.

Returns whether the method is const qualified.

This function was introduced in Qt 6.2.

Returns true if this method is valid (can be introspected and invoked), otherwise returns false.

This function was introduced in Qt 5.0.

Returns this method's index.

Returns the signature of this method (e.g., setValue(double)).

This function was introduced in Qt 5.0.

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Returns the type of this method (signal, slot, or method).

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Returns the name of this method.

This function was introduced in Qt 5.0.

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Returns the number of parameters of this method.

This function was introduced in Qt 5.0.

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Returns the metatype of the parameter at the given index.

If the index is smaller than zero or larger than parameterCount(), an invalid QMetaType is returned.

This function was introduced in Qt 6.0.

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Returns a list of parameter names.

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Returns the type of the parameter at the given index.

The return value is one of the types that are registered with QMetaType, or QMetaType::UnknownType if the type is not registered.

This function was introduced in Qt 5.0.

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Returns the name of the type at position index If there is no parameter at index, returns an empty QByteArray

This function was introduced in Qt 6.0.

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Returns a list of parameter types.

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Returns this method's local index inside.

This function was introduced in Qt 6.0.

Returns the return type of this method.

This function was introduced in Qt 6.0.

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Returns the return type of this method.

The return value is one of the types that are registered with QMetaType, or QMetaType::UnknownType if the type is not registered.

This function was introduced in Qt 5.0.

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Returns the method revision if one was specified by Q_REVISION, otherwise returns 0.

This function was introduced in Qt 5.1.

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.

Returns the return type name of this method.

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This is an overloaded function.

Returns true if method m1 is not equal to method m2, otherwise returns false.

This function was introduced in Qt 5.0.

This is an overloaded function.

Returns true if method m1 is equal to method m2, otherwise returns false.

This function was introduced in Qt 5.0.

Equals maximum number of arguments available for execution of the method via QMetaMethod::invoke()