Contents

Source implementation

QMetaObject Class Reference

The QMetaObject class contains meta-information about Qt objects.

  1. #include <QMetaObject>

Detailed Description

The QMetaObject class contains meta-information about Qt objects.

The Qt Meta-Object System in Qt is responsible for the signals and slots inter-object communication mechanism, runtime type information, and the Qt property system. A single QMetaObject instance is created for each QObject subclass that is used in an application, and this instance stores all the meta-information for the QObject subclass. This object is available as QObject::metaObject().

This class is not normally required for application programming, but it is useful if you write meta-applications, such as scripting engines or GUI builders.

The functions you are most likely to find useful are these:

The index functions indexOfConstructor(), indexOfMethod(), indexOfEnumerator(), and indexOfProperty() map names of constructors, member functions, enumerators, or properties to indexes in the meta-object. For example, Qt uses indexOfMethod() internally when you connect a signal to a slot.

Classes can also have a list of name--value pairs of additional class information, stored in QMetaClassInfo objects. The number of pairs is returned by classInfoCount(), single pairs are returned by classInfo(), and you can search for pairs with indexOfClassInfo().

See also QMetaClassInfo, QMetaEnum, QMetaMethod, QMetaProperty, QMetaType, and Meta-Object System.

Public Functions

Toggle details bool QMetaObject

checkConnectArgscheckConnectArgs ( const char *signal , const char *method ...) ( const char *signal , const char *method ) [static]

Returns true if the signal and method arguments are compatible; otherwise returns false.

Both signal and method are expected to be normalized.

See also normalizedSignature().

Look up this member in the source code.

Toggle details QMetaClassInfo QMetaObject

classInfoclassInfo ( int index ) ( int index )const

Returns the meta-data for the item of class information with the given index.

Example:

  1. class MyClass : public QObject
  2.  {
  3.     Q_OBJECT
  4.     Q_CLASSINFO("author", "Sabrina Schweinsteiger")
  5.     Q_CLASSINFO("url", "http://doc.moosesoft.co.uk/1.0/")
  6.  
  7. public:
  8.     ...
  9. };

See also classInfoCount(), classInfoOffset(), and indexOfClassInfo().

Look up this member in the source code.

Toggle details int QMetaObject

classInfoCountclassInfoCount () ()const

Returns the number of items of class information in this class.

See also classInfo(), classInfoOffset(), and indexOfClassInfo().

Look up this member in the source code.

Toggle details int QMetaObject

classInfoOffsetclassInfoOffset () ()const

Returns the class information offset for this class; i.e. the index position of this class's first class information item.

If the class has no superclasses with class information, the offset is 0; otherwise the offset is the sum of all the class information items in the class's superclasses.

See also classInfo(), classInfoCount(), and indexOfClassInfo().

Look up this member in the source code.

Toggle details const char * QMetaObject

classNameclassName () ()const

Returns the class name.

See also superClass().

Look up this member in the source code.

Toggle details void QMetaObject

connectSlotsByNameconnectSlotsByName ( QObject *object ) ( QObject *object ) [static]

Searches recursively for all child objects of the given object, and connects matching signals from them to slots of object that follow the following form:

  1. void on_<object name>_<signal name>(<signal parameters>);

Let's assume our object has a child object of type QPushButton with the object name button1. The slot to catch the button's clicked() signal would be:

  1. void on_button1_clicked();

See also QObject::setObjectName().

Look up this member in the source code.

Toggle details QMetaMethod QMetaObject

constructorconstructor ( int index ) ( int index )const

Returns the meta-data for the constructor with the given index.

See also constructorCount() and newInstance().

Look up this member in the source code.

Toggle details int QMetaObject

constructorCountconstructorCount () ()const

Returns the number of constructors in this class.

See also constructor() and indexOfConstructor().

Look up this member in the source code.

Toggle details QMetaEnum QMetaObject

enumeratorenumerator ( int index ) ( int index )const

Returns the meta-data for the enumerator with the given index.

See also enumeratorCount(), enumeratorOffset(), and indexOfEnumerator().

Look up this member in the source code.

Toggle details int QMetaObject

enumeratorCountenumeratorCount () ()const

Returns the number of enumerators in this class.

See also enumerator(), enumeratorOffset(), and indexOfEnumerator().

Look up this member in the source code.

Toggle details int QMetaObject

enumeratorOffsetenumeratorOffset () ()const

Returns the enumerator offset for this class; i.e. the index position of this class's first enumerator.

If the class has no superclasses with enumerators, the offset is 0; otherwise the offset is the sum of all the enumerators in the class's superclasses.

See also enumerator(), enumeratorCount(), and indexOfEnumerator().

Look up this member in the source code.

Toggle details int QMetaObject

indexOfClassInfoindexOfClassInfo ( const char *name ) ( const char *name )const

Finds class information item name and returns its index; otherwise returns -1.

See also classInfo(), classInfoCount(), and classInfoOffset().

Look up this member in the source code.

Toggle details int QMetaObject

indexOfConstructorindexOfConstructor ( const char *constructor ) ( const char *constructor )const

Finds constructor and returns its index; otherwise returns -1.

Note that the constructor has to be in normalized form, as returned by normalizedSignature().

See also constructor(), constructorCount(), and normalizedSignature().

Look up this member in the source code.

Toggle details int QMetaObject

indexOfEnumeratorindexOfEnumerator ( const char *name ) ( const char *name )const

Finds enumerator name and returns its index; otherwise returns -1.

See also enumerator(), enumeratorCount(), and enumeratorOffset().

Look up this member in the source code.

Toggle details int QMetaObject

indexOfMethodindexOfMethod ( const char *method ) ( const char *method )const

Finds method and returns its index; otherwise returns -1.

Note that the method has to be in normalized form, as returned by normalizedSignature().

See also method(), methodCount(), methodOffset(), and normalizedSignature().

Look up this member in the source code.

Toggle details int QMetaObject

indexOfPropertyindexOfProperty ( const char *name ) ( const char *name )const

Finds property name and returns its index; otherwise returns -1.

See also property(), propertyCount(), and propertyOffset().

Look up this member in the source code.

Toggle details int QMetaObject

indexOfSignalindexOfSignal ( const char *signal ) ( const char *signal )const

Finds signal and returns its index; otherwise returns -1.

This is the same as indexOfMethod(), except that it will return -1 if the method exists but isn't a signal.

Note that the signal has to be in normalized form, as returned by normalizedSignature().

See also indexOfMethod(), normalizedSignature(), method(), methodCount(), and methodOffset().

Look up this member in the source code.

Toggle details int QMetaObject

indexOfSlotindexOfSlot ( const char *slot ) ( const char *slot )const

Finds slot and returns its index; otherwise returns -1.

This is the same as indexOfMethod(), except that it will return -1 if the method exists but isn't a slot.

See also indexOfMethod(), method(), methodCount(), and methodOffset().

Look up this member in the source code.

Toggle details bool QMetaObject

invokeMethodinvokeMethod ( QObject *obj , const char *member , Qt::ConnectionType type , QGenericReturnArgument ret , QGenericArgument val0=QGenericArgument( 0 ) , QGenericArgument val1=QGenericArgument() , QGenericArgument val2=QGenericArgument() , QGenericArgument val3=QGenericArgument() , QGenericArgument val4=QGenericArgument() , QGenericArgument val5=QGenericArgument() , QGenericArgument val6=QGenericArgument() , QGenericArgument val7=QGenericArgument() , QGenericArgument val8=QGenericArgument() , QGenericArgument val9=QGenericArgument() ...) ( QObject *obj , const char *member , Qt::ConnectionType type , QGenericReturnArgument ret , QGenericArgument val0=QGenericArgument( 0 ) , QGenericArgument val1=QGenericArgument() , QGenericArgument val2=QGenericArgument() , QGenericArgument val3=QGenericArgument() , QGenericArgument val4=QGenericArgument() , QGenericArgument val5=QGenericArgument() , QGenericArgument val6=QGenericArgument() , QGenericArgument val7=QGenericArgument() , QGenericArgument val8=QGenericArgument() , QGenericArgument val9=QGenericArgument() ) [static]

Invokes the member (a signal or a slot name) on the object obj. 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 type:

  • If type is Qt::DirectConnection, the member will be invoked immediately.
  • If type is Qt::QueuedConnection, a QEvent will be sent and the member is invoked as soon as the application enters the main event loop.
  • If type is Qt::BlockingQueuedConnection, the method will be invoked in the same way as for Qt::QueuedConnection, except that the current thread will block until the event is delivered. Using this connection type to communicate between objects in the same thread will lead to deadlocks.
  • If type is Qt::AutoConnection, the member is invoked synchronously if obj lives in the same thread as the caller; otherwise it will invoke the member asynchronously.

The return value of the member function call is placed in ret. 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 the member function.

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.

You only need to pass the name of the signal or slot to this function, not the entire signature. For example, to asynchronously invoke the animateClick() slot on a QPushButton, use the following code:

  1.                     QMetaObject::invokeMethod(pushButton, "animateClick",
  2.                           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

  1.                     QMetaObject::invokeMethod: Unable to handle unregistered datatype 'MyType'

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

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

  1.                     QString retVal;
  2. QMetaObject::invokeMethod(obj, "compute", Qt::DirectConnection,
  3.                           Q_RETURN_ARG(QString, retVal),
  4.                           Q_ARG(QString, "sqrt"),
  5.                           Q_ARG(int, 42),
  6.                           Q_ARG(double, 9.7));

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

See also Q_ARG(), Q_RETURN_ARG(), qRegisterMetaType(), and QMetaMethod::invoke().

Look up this member in the source code.

Toggle details bool QMetaObject

invokeMethodinvokeMethod ( QObject *obj , const char *member , QGenericReturnArgument ret , QGenericArgument val0=QGenericArgument( 0 ) , QGenericArgument val1=QGenericArgument() , QGenericArgument val2=QGenericArgument() , QGenericArgument val3=QGenericArgument() , QGenericArgument val4=QGenericArgument() , QGenericArgument val5=QGenericArgument() , QGenericArgument val6=QGenericArgument() , QGenericArgument val7=QGenericArgument() , QGenericArgument val8=QGenericArgument() , QGenericArgument val9=QGenericArgument() ...) ( QObject *obj , const char *member , QGenericReturnArgument ret , QGenericArgument val0=QGenericArgument( 0 ) , QGenericArgument val1=QGenericArgument() , QGenericArgument val2=QGenericArgument() , QGenericArgument val3=QGenericArgument() , QGenericArgument val4=QGenericArgument() , QGenericArgument val5=QGenericArgument() , QGenericArgument val6=QGenericArgument() , QGenericArgument val7=QGenericArgument() , QGenericArgument val8=QGenericArgument() , QGenericArgument val9=QGenericArgument() ) [static]

This function overloads invokeMethod().

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

Look up this member in the source code.

Toggle details bool QMetaObject

invokeMethodinvokeMethod ( QObject *obj , const char *member , Qt::ConnectionType type , QGenericArgument val0=QGenericArgument( 0 ) , QGenericArgument val1=QGenericArgument() , QGenericArgument val2=QGenericArgument() , QGenericArgument val3=QGenericArgument() , QGenericArgument val4=QGenericArgument() , QGenericArgument val5=QGenericArgument() , QGenericArgument val6=QGenericArgument() , QGenericArgument val7=QGenericArgument() , QGenericArgument val8=QGenericArgument() , QGenericArgument val9=QGenericArgument() ...) ( QObject *obj , const char *member , Qt::ConnectionType type , QGenericArgument val0=QGenericArgument( 0 ) , QGenericArgument val1=QGenericArgument() , QGenericArgument val2=QGenericArgument() , QGenericArgument val3=QGenericArgument() , QGenericArgument val4=QGenericArgument() , QGenericArgument val5=QGenericArgument() , QGenericArgument val6=QGenericArgument() , QGenericArgument val7=QGenericArgument() , QGenericArgument val8=QGenericArgument() , QGenericArgument val9=QGenericArgument() ) [static]

This function overloads invokeMethod().

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

Look up this member in the source code.

Toggle details bool QMetaObject

invokeMethodinvokeMethod ( QObject *obj , const char *member , QGenericArgument val0=QGenericArgument( 0 ) , QGenericArgument val1=QGenericArgument() , QGenericArgument val2=QGenericArgument() , QGenericArgument val3=QGenericArgument() , QGenericArgument val4=QGenericArgument() , QGenericArgument val5=QGenericArgument() , QGenericArgument val6=QGenericArgument() , QGenericArgument val7=QGenericArgument() , QGenericArgument val8=QGenericArgument() , QGenericArgument val9=QGenericArgument() ...) ( QObject *obj , const char *member , QGenericArgument val0=QGenericArgument( 0 ) , QGenericArgument val1=QGenericArgument() , QGenericArgument val2=QGenericArgument() , QGenericArgument val3=QGenericArgument() , QGenericArgument val4=QGenericArgument() , QGenericArgument val5=QGenericArgument() , QGenericArgument val6=QGenericArgument() , QGenericArgument val7=QGenericArgument() , QGenericArgument val8=QGenericArgument() , QGenericArgument val9=QGenericArgument() ) [static]

This function overloads invokeMethod().

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

Look up this member in the source code.

Toggle details QMetaMethod QMetaObject

methodmethod ( int index ) ( int index )const

Returns the meta-data for the method with the given index.

See also methodCount(), methodOffset(), and indexOfMethod().

Look up this member in the source code.

Toggle details int QMetaObject

methodCountmethodCount () ()const

Returns the number of methods in this class, including the number of properties provided by each base class. These include signals and slots as well as normal member functions.

Use code like the following to obtain a QStringList containing the methods specific to a given class:

  1. const QMetaObject* metaObject = obj->metaObject();
  2. QStringList methods;
  3. for(int i = metaObject->methodOffset(); i < metaObject->methodCount(); ++i)
  4.     methods << QString::fromLatin1(metaObject->method(i).signature());

See also method(), methodOffset(), and indexOfMethod().

Look up this member in the source code.

Toggle details int QMetaObject

methodOffsetmethodOffset () ()const

Returns the method offset for this class; i.e. the index position of this class's first member function.

The offset is the sum of all the methods in the class's superclasses (which is always positive since QObject has the deleteLater() slot and a destroyed() signal).

See also method(), methodCount(), and indexOfMethod().

Look up this member in the source code.

Toggle details QObject * QMetaObject

newInstancenewInstance ( QGenericArgument val0=QGenericArgument( 0 ) , QGenericArgument val1=QGenericArgument() , QGenericArgument val2=QGenericArgument() , QGenericArgument val3=QGenericArgument() , QGenericArgument val4=QGenericArgument() , QGenericArgument val5=QGenericArgument() , QGenericArgument val6=QGenericArgument() , QGenericArgument val7=QGenericArgument() , QGenericArgument val8=QGenericArgument() , QGenericArgument val9=QGenericArgument() ...) ( QGenericArgument val0=QGenericArgument( 0 ) , QGenericArgument val1=QGenericArgument() , QGenericArgument val2=QGenericArgument() , QGenericArgument val3=QGenericArgument() , QGenericArgument val4=QGenericArgument() , QGenericArgument val5=QGenericArgument() , QGenericArgument val6=QGenericArgument() , QGenericArgument val7=QGenericArgument() , QGenericArgument val8=QGenericArgument() , QGenericArgument val9=QGenericArgument() )const

Constructs a new instance of this class. You can pass up to ten arguments (val0, val1, val2, val3, val4, val5, val6, val7, val8, and val9) to the constructor. Returns the new object, or 0 if no suitable constructor is available.

Note that only constructors that are declared with the Q_INVOKABLE modifier are made available through the meta-object system.

See also Q_ARG() and constructor().

Look up this member in the source code.

Toggle details QByteArray QMetaObject

normalizedSignaturenormalizedSignature ( const char *method ( const char *method ) [static]

Normalizes the signature of the given method.

Qt uses normalized signatures to decide whether two given signals and slots are compatible. Normalization reduces whitespace to a minimum, moves 'const' to the front where appropriate, removes 'const' from value types and replaces const references with values.

See also checkConnectArgs() and normalizedType().

Look up this member in the source code.

Toggle details QByteArray QMetaObject

normalizedTypenormalizedType ( const char *type ) ( const char *type ) [static]

Normalizes a type.

See QMetaObject::normalizedSignature() for a description on how Qt normalizes.

Example:

  1.                     QByteArray normType = QMetaObject::normalizedType(" int    const  *");
  2. // normType is now "const int*"

See also normalizedSignature().

Look up this member in the source code.

Toggle details QMetaProperty QMetaObject

propertyproperty ( int index ) ( int index )const

Returns the meta-data for the property with the given index. If no such property exists, a null QMetaProperty is returned.

See also propertyCount(), propertyOffset(), and indexOfProperty().

Look up this member in the source code.

Toggle details int QMetaObject

propertyCountpropertyCount () ()const

Returns the number of properties in this class, including the number of properties provided by each base class.

Use code like the following to obtain a QStringList containing the properties specific to a given class:

  1. const QMetaObject* metaObject = obj->metaObject();
  2. QStringList properties;
  3. for(int i = metaObject->propertyOffset(); i < metaObject->propertyCount(); ++i)
  4.     properties << QString::fromLatin1(metaObject->property(i).name());

See also property(), propertyOffset(), and indexOfProperty().

Look up this member in the source code.

Toggle details int QMetaObject

propertyOffsetpropertyOffset () ()const

Returns the property offset for this class; i.e. the index position of this class's first property.

The offset is the sum of all the properties in the class's superclasses (which is always positive since QObject has the name() property).

See also property(), propertyCount(), and indexOfProperty().

Look up this member in the source code.

Toggle details const QMetaObject * QMetaObject

superClasssuperClass () ()const

Returns the meta-object of the superclass, or 0 if there is no such object.

See also className().

Look up this member in the source code.

Toggle details QMetaProperty QMetaObject

userPropertyuserProperty () ()const

Returns the property that has the USER flag set to true.

See also QMetaProperty::isUser().

Look up this member in the source code.

    Macros

    Toggle detailsQ_ARGQ_ARG ( Type , value )

    This macro takes a Type and a value of that type and returns a QGenericArgument object that can be passed to QMetaObject::invokeMethod().

    See also Q_RETURN_ARG().

    Toggle detailsQ_RETURN_ARGQ_RETURN_ARG ( Type , value )

    This macro takes a Type and a non-const reference to a value of that type and returns a QGenericReturnArgument object that can be passed to QMetaObject::invokeMethod().

    See also Q_ARG().

      You may use the documentation under the terms of the GNU Free Documentation License version 1.3, as published by the Free Software Foundation. Alternatively, you may use the documentation in accordance with the terms contained in a written agreement between you and Digia.

      Hide Notes

      Notes provided by the Qt Community

      No notes

      Creative Commons Attribution-ShareAlike 2.5 Generic

      Community Notes are available under

      Attribution-Share Alike 2.5 Generic