QCustomEvent Class Reference

Detailed Description

QCustomEvent is a generic event class for user-defined events. User defined events can be sent to widgets or other QObject instances using QApplication::postEvent() or QApplication::sendEvent(). Subclasses of QObject can easily receive custom events by implementing the QObject::customEvent() event handler function.

QCustomEvent objects should be created with a type ID that uniquely identifies the event type. To avoid clashes with the Qt-defined events types, the value should be at least as large as the value of the "User" entry in the QEvent::Type enum.

QCustomEvent contains a generic void* data member that may be used for transferring event-specific data to the receiver. Note that since events are normally delivered asynchronously, the data pointer, if used, must remain valid until the event has been received and processed.

QCustomEvent can be used as-is for simple user-defined event types, but normally you will want to make a subclass of it for your event types. In a subclass, you can add data members that are suitable for your event type.

Example:

    class ColorChangeEvent : public QCustomEvent
    {
    public:
        ColorChangeEvent( QColor color )
            : QCustomEvent( 65432 ), c( color ) {}
        QColor color() const { return c; }
    private:
        QColor c;
    };

    // To send an event of this custom event type:

    ColorChangeEvent* ce = new ColorChangeEvent( blue );
    QApplication::postEvent( receiver, ce );  // Qt will delete it when done

    // To receive an event of this custom event type:

    void MyWidget::customEvent( QCustomEvent * e )
    {
        if ( e->type() == 65432 ) {  // It must be a ColorChangeEvent
            ColorChangeEvent* ce = (ColorChangeEvent*)e;
            newColor = ce->color();
        }
    }
    

See also QWidget::customEvent(), QApplication::notify(), and Event Classes.

Member Function Documentation

QCustomEvent::QCustomEvent ( int type )

QCustomEvent::QCustomEvent ( Type type, void * data )

Constructs a custom event object with the event type type and a pointer to data. (Note that any int value may safely be cast to QEvent::Type).

void * QCustomEvent::data () const

Returns a pointer to the generic event data.

See also setData().

void QCustomEvent::setData ( void * data )

Sets the generic data pointer to data.

See also data().

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