QAbstractEventDispatcher Class

The QAbstractEventDispatcher class provides an interface to manage Qt's event queue. More...

Header: #include <QAbstractEventDispatcher>
Inherits: QObject

Public Types

typedef EventFilter
typedef TimerInfo

Public Functions

QAbstractEventDispatcher(QObject * parent = 0)
bool filterEvent(void * message)
virtual void flush() = 0
virtual bool hasPendingEvents() = 0
virtual void interrupt() = 0
virtual bool processEvents(QEventLoop::ProcessEventsFlags flags) = 0
virtual void registerSocketNotifier(QSocketNotifier * notifier) = 0
int registerTimer(int interval, QObject * object)
virtual void registerTimer(int timerId, int interval, QObject * object) = 0
virtual QList<TimerInfo> registeredTimers(QObject * object) const = 0
EventFilter setEventFilter(EventFilter filter)
virtual void unregisterSocketNotifier(QSocketNotifier * notifier) = 0
virtual bool unregisterTimer(int timerId) = 0
virtual bool unregisterTimers(QObject * object) = 0
virtual void wakeUp() = 0
  • 29 public functions inherited from QObject


void aboutToBlock()
void awake()

Static Public Members

QAbstractEventDispatcher * instance(QThread * thread = 0)
  • 7 static public members inherited from QObject

Additional Inherited Members

  • 1 property inherited from QObject
  • 1 public slot inherited from QObject
  • 8 protected functions inherited from QObject

Detailed Description

The QAbstractEventDispatcher class provides an interface to manage Qt's event queue.

An event dispatcher receives events from the window system and other sources. It then sends them to the QCoreApplication or QApplication instance for processing and delivery. QAbstractEventDispatcher provides fine-grained control over event delivery.

For simple control of event processing use QCoreApplication::processEvents().

For finer control of the application's event loop, call instance() and call functions on the QAbstractEventDispatcher object that is returned. If you want to use your own instance of QAbstractEventDispatcher or of a QAbstractEventDispatcher subclass, you must create your instance before you create the QApplication object.

The main event loop is started by calling QCoreApplication::exec(), and stopped by calling QCoreApplication::exit(). Local event loops can be created using QEventLoop.

Programs that perform long operations can call processEvents() with a bitwise OR combination of various QEventLoop::ProcessEventsFlag values to control which events should be delivered.

QAbstractEventDispatcher also allows the integration of an external event loop with the Qt event loop. For example, the Motif Extension includes a reimplementation of QAbstractEventDispatcher that merges Qt and Motif events together.

See also QEventLoop and QCoreApplication.

Member Type Documentation

typedef QAbstractEventDispatcher::EventFilter

Typedef for a function with the signature

bool myEventFilter(void *message);

Note that the type of the message is platform dependent. The following table shows the message's type on Windows, Mac, X11 and BlackBerry. You can do a static cast to these types.


See also setEventFilter() and filterEvent().

typedef QAbstractEventDispatcher::TimerInfo

Typedef for QPair<int, int>. The first component of the pair is the timer ID; the second component is the interval.

See also registeredTimers().

Member Function Documentation

QAbstractEventDispatcher::QAbstractEventDispatcher(QObject * parent = 0)

Constructs a new event dispatcher with the given parent.


Destroys the event dispatcher.

[signal] void QAbstractEventDispatcher::aboutToBlock()

This signal is emitted before the event loop calls a function that could block.

See also awake().

[signal] void QAbstractEventDispatcher::awake()

This signal is emitted after the event loop returns from a function that could block.

See also wakeUp() and aboutToBlock().

bool QAbstractEventDispatcher::filterEvent(void * message)

Sends message through the event filter that was set by setEventFilter(). If no event filter has been set, this function returns false; otherwise, this function returns the result of the event filter function.

Subclasses of QAbstractEventDispatcher must call this function for all messages received from the system to ensure compatibility with any extensions that may be used in the application.

Note that the type of message is platform dependent. See QAbstractEventDispatcher::EventFilter for details.

See also setEventFilter().

[pure virtual] void QAbstractEventDispatcher::flush()

Flushes the event queue. This normally returns almost immediately. Does nothing on platforms other than X11.

[pure virtual] bool QAbstractEventDispatcher::hasPendingEvents()

Returns true if there is an event waiting; otherwise returns false.

[static] QAbstractEventDispatcher * QAbstractEventDispatcher::instance(QThread * thread = 0)

Returns a pointer to the event dispatcher object for the specified thread. If thread is zero, the current thread is used. If no event dispatcher exists for the specified thread, this function returns 0.

Note: If Qt is built without thread support, the thread argument is ignored.

[pure virtual] void QAbstractEventDispatcher::interrupt()

Interrupts event dispatching; i.e. the event dispatcher will return from processEvents() as soon as possible.

[pure virtual] bool QAbstractEventDispatcher::processEvents(QEventLoop::ProcessEventsFlags flags)

Processes pending events that match flags until there are no more events to process. Returns true if an event was processed; otherwise returns false.

This function is especially useful if you have a long running operation and want to show its progress without allowing user input; i.e. by using the QEventLoop::ExcludeUserInputEvents flag.

If the QEventLoop::WaitForMoreEvents flag is set in flags, the behavior of this function is as follows:

  • If events are available, this function returns after processing them.
  • If no events are available, this function will wait until more are available and return after processing newly available events.

If the QEventLoop::WaitForMoreEvents flag is not set in flags, and no events are available, this function will return immediately.

Note: This function does not process events continuously; it returns after all available events are processed.

See also hasPendingEvents().

[pure virtual] void QAbstractEventDispatcher::registerSocketNotifier(QSocketNotifier * notifier)

Registers notifier with the event loop. Subclasses must implement this method to tie a socket notifier into another event loop.

int QAbstractEventDispatcher::registerTimer(int interval, QObject * object)

Registers a timer with the specified interval for the given object.

[pure virtual] void QAbstractEventDispatcher::registerTimer(int timerId, int interval, QObject * object)

Register a timer with the specified timerId and interval for the given object.

[pure virtual] QList<TimerInfo> QAbstractEventDispatcher::registeredTimers(QObject * object) const

Returns a list of registered timers for object. The timer ID is the first member in each pair; the interval is the second.

EventFilter QAbstractEventDispatcher::setEventFilter(EventFilter filter)

Replaces the event filter function for this QAbstractEventDispatcher with filter and returns the replaced event filter function. Only the current event filter function is called. If you want to use both filter functions, save the replaced EventFilter in a place where yours can call it.

The event filter function set here is called for all messages taken from the system event loop before the event is dispatched to the respective target, including the messages not meant for Qt objects.

The event filter function should return true if the message should be filtered, (i.e. stopped). It should return false to allow processing the message to continue.

By default, no event filter function is set (i.e., this function returns a null EventFilter the first time it is called).

[pure virtual] void QAbstractEventDispatcher::unregisterSocketNotifier(QSocketNotifier * notifier)

Unregisters notifier from the event dispatcher. Subclasses must reimplement this method to tie a socket notifier into another event loop. Reimplementations must call the base implementation.

[pure virtual] bool QAbstractEventDispatcher::unregisterTimer(int timerId)

Unregisters the timer with the given timerId. Returns true if successful; otherwise returns false.

See also registerTimer() and unregisterTimers().

[pure virtual] bool QAbstractEventDispatcher::unregisterTimers(QObject * object)

Unregisters all the timers associated with the given object. Returns true if all timers were successful removed; otherwise returns false.

See also unregisterTimer() and registeredTimers().

[pure virtual] void QAbstractEventDispatcher::wakeUp()

Wakes up the event loop.

Note: This function is thread-safe.

See also awake().

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