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QCustomEvent Class Reference

The QCustomEvent class provides support for custom events. More...

#include <qevent.h>

Inherits QEvent.

List of all member functions.

Public Members

QCustomEvent ( int type )
QCustomEvent ( Type type, void * data )
void* data () const
void setData ( void * data )

Detailed Description

The QCustomEvent class provides support for custom events.

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 QWidget can easily receive custom events by implementing the QWidget::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( 346798 ), 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() == 346798 ) {              // It must be a ColorChangeEvent
      ColorChangeEvent* ce = (ColorChangeEvent*)e;
      newColor = ce->color();
    }
  }

See also QWidget::customEvent() and QApplication::notify().

Member Function Documentation

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).

QCustomEvent::QCustomEvent ( int type )

Constructs a custom event object with event type type. The value of type must be at least as large as QEvent::User. The data pointer is set to 0.

void * QCustomEvent::data () const

Returns a pointer to the generic event data.

void QCustomEvent::setData ( void * data )

Sets the generic data pointer to data.