QAbstractEventDispatcher Class▲

  • Header: QAbstractEventDispatcher

  • CMake:

    find_package(Qt6 REQUIRED COMPONENTS Core)

    target_link_libraries(mytarget PRIVATE Qt6::Core)

  • qmake: QT += core

  • Inherits: QObject

  • Inherited By:

  • Group: QAbstractEventDispatcher is part of Event Classes

Detailed Description▲

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 install it with QCoreApplication::setEventDispatcher() or QThread::setEventDispatcher() before a default event dispatcher has been installed.

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.

See Also▲

See also QEventLoop, QCoreApplication, QThread

Member Function Documentation▲

 

[explicit] QAbstractEventDispatcher::QAbstractEventDispatcher(QObject *parent = nullptr)▲

Constructs a new event dispatcher with the given parent.

[virtual] QAbstractEventDispatcher::~QAbstractEventDispatcher()▲

Destroys the event dispatcher.

void QAbstractEventDispatcher::aboutToBlock()▲

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

See Also▲

See also awake()

void QAbstractEventDispatcher::awake()▲

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

See Also▲

See also wakeUp(), aboutToBlock()

[since 5.0] bool QAbstractEventDispatcher::filterNativeEvent(const QByteArray &eventType, void *message, qintptr *result)▲

Sends message through the event filters that were set by installNativeEventFilter(). This function returns true as soon as an event filter returns true, and false otherwise to indicate that the processing of the event should continue.

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. The type of event eventType is specific to the platform plugin chosen at run-time, and can be used to cast message to the right type. The result pointer is only used on Windows, and corresponds to the LRESULT pointer.

Note that the type of message is platform dependent. See QAbstractNativeEventFilter for details.

This function was introduced in Qt 5.0.

See Also▲

See also installNativeEventFilter(), QAbstractNativeEventFilter::nativeEventFilter()

[since 5.0] void QAbstractEventDispatcher::installNativeEventFilter(QAbstractNativeEventFilter *filterObj)▲

Installs an event filter filterObj for all native events received by the application.

The event filter filterObj receives events via its nativeEventFilter() function, which is called for all events received by all threads.

The nativeEventFilter() function should return true if the event should be filtered, (in this case, stopped). It should return false to allow normal Qt processing to continue: the native event can then be translated into a QEvent and handled by the standard Qt event filtering, e.g. QObject::installEventFilter().

If multiple event filters are installed, the filter that was installed last is activated first.

The filter function set here receives native messages, that is, MSG or XEvent structs.

For maximum portability, you should always try to use QEvent objects and QObject::installEventFilter() whenever possible.

This function was introduced in Qt 5.0.

See Also▲

See also QObject::installEventFilter()

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

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

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

[pure virtual] void QAbstractEventDispatcher::interrupt()▲

Interrupts event dispatching. 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 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.

[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(qint64 interval, Qt::TimerType timerType, QObject *object)▲

Registers a timer with the specified interval and timerType for the given object and returns the timer id.

[pure virtual] void QAbstractEventDispatcher::registerTimer(int timerId, qint64 interval, Qt::TimerType timerType, QObject *object)▲

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

[pure virtual] QList<QAbstractEventDispatcher::TimerInfo> QAbstractEventDispatcher