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QEvent Class Reference

The QEvent class is the base class of all event classes. Event objects contain event parameters. More...

#include <QEvent>

Inherited by QTimerEvent, QChildEvent, QCustomEvent, QInputEvent, QFocusEvent, QPaintEvent, QMoveEvent, QResizeEvent, QCloseEvent, QIconDragEvent, QShowEvent, QHideEvent, QDropEvent, QDragLeaveEvent, QFileOpenEvent, and QToolBarChangeEvent.

Public Types

Writable Properties

Public Functions


Detailed Description

The QEvent class is the base class of all event classes. Event objects contain event parameters.

Qt's main event loop (QApplication::exec()) fetches native window system events from the event queue, translates them into QEvents, and sends the translated events to QObjects.

In general, events come from the underlying window system (spontaneous() returns true), but it is also possible to manually send events using QApplication::sendEvent() and QApplication::postEvent() (spontaneous() returns false).

QObjects receive events by having their QObject::event() function called. The function can be reimplemented in subclasses to customize event handling and add additional event types; QWidget::event() is a notable example. By default, events are dispatched to event handlers like QObject::timerEvent() and QWidget::mouseMoveEvent(). QObject::installEventFilter() allows an object to intercept events destined for another object.

The basic QEvent contains only an event type parameter and an accept flag. The accept flag set with accept(), and cleared with ignore(). It is set by default, but don't rely on this as subclasses may choose to clear it in their constructor.

Subclasses of QEvent contain additional parameters that describe the particular event.

QWidget::event() QApplication::sendEvent() QApplication::postEvent() QApplication::processEvents()

See also QObject::event() and QObject::installEventFilter().


Member Type Documentation

enum QEvent::Type

This enum type defines the valid event types in Qt. The event types and the specialized classes for each type are as follows:

QEvent::NoneNot an event.
QEvent::AccessibilityAccessibility information is requested.
QEvent::AccessibilityHelpUsed to query for additional information about complex widgets. QAccessibleEvent
QEvent::ActionChangedAn action has been changed.
QEvent::ActionAddedA new action has been added.
QEvent::ActionRemovedAn action has been removed.
QEvent::ActivationChangeA widget's top-level window activation state has changed.
QEvent::ApplicationWindowIconChangeThe application's icon has changed.
QEvent::ApplicationFontChangeThe default application font has changed.
QEvent::ApplicationPaletteChangeThe default application palette has changed.
QEvent::ChildAddedAn object gets a child, QChildEvent.
QEvent::ChildPolishedA widget child gets polished, QChildEvent.
QEvent::ChildRemovedAn object loses a child, QChildEvent.
QEvent::ClipboardThe clipboard contents have changed.
QEvent::CloseWidget was closed (permanently), QCloseEvent.
QEvent::ContextMenuContext popup menu, QContextMenuEvent
QEvent::CreateReserved.
QEvent::DeferredDeleteThe object will be deleted after it has cleaned up.
QEvent::DestroyReserved.
QEvent::DragEnterThe cursor enters a widget during a drag and drop action, QDragEnterEvent.
QEvent::DragLeaveThe cursor leaves a widget during a drag and drop action, QDragLeaveEvent.
QEvent::DragMoveA drag and drop action is in progress, QDragMoveEvent.
QEvent::DropA drag and drop action is completed, QDropEvent.
QEvent::EnabledChangeWidget's enabled state has changed
QEvent::EnterMouse enters widget's boundaries.
QEvent::FileOpenFile open request.
QEvent::FocusInWidget gains keyboard focus, QFocusEvent.
QEvent::FocusOutWidget loses keyboard focus, QFocusEvent.
QEvent::FontChangeWidget's font has changed
QEvent::HideWidget was hidden, QHideEvent.
QEvent::HideToParentA child widget has been hidden.
QEvent::IMComposeInput method composition is taking place, QIMEvent.
QEvent::IMEndThe end of input method composition, QIMEvent.
QEvent::IMStartThe start of input method composition, QIMEvent.
QEvent::IconTextChangeWidget's icon text has been changed
QEvent::KeyPressKey press (including Shift, for example), QKeyEvent.
QEvent::KeyReleaseKey release, QKeyEvent.
QEvent::LanguageChangeThe application translation changed, QTranslator
QEvent::LayoutDirectionChangeThe direction of layouts changed
QEvent::LayoutRequestWidget layout needs to be redone.
QEvent::LeaveMouse leaves widget's boundaries.
QEvent::LocaleChangeThe system locale changed
QEvent::MetaCall 
QEvent::ModifiedChangeWidgets modification state has been changed
QEvent::MouseButtonDblClickMouse press again, QMouseEvent.
QEvent::MouseButtonPressMouse press, QMouseEvent.
QEvent::MouseButtonReleaseMouse release, QMouseEvent.
QEvent::MouseMoveMouse move, QMouseEvent.
QEvent::MouseTrackingChangeThe mouse tracking state has changed.
QEvent::MoveWidget's position changed, QMoveEvent.
QEvent::PaintScreen update necessary, QPaintEvent.
QEvent::PaletteChangePalette of the widget changed.
QEvent::PolishThe widget is polished.
QEvent::PolishRequestThe widget should be polished.
QEvent::QuitReserved.
QEvent::ParentChangeReserved.
QEvent::ResizeWidget's size changed, QResizeEvent.
QEvent::ShortcutKey press in child for shortcut key handling, QKeyEvent.
QEvent::ShortcutOverrideKey press in child, for overriding shortcut key handling, QKeyEvent.
QEvent::ShowWidget was shown on screen, QShowEvent.
QEvent::ShowFullScreenWidget should be shown full-screen (obsolete).
QEvent::ShowMaximizedWidget should be shown maximized (obsolete).
QEvent::ShowMinimizedWidget should be shown minimized (obsolete).
QEvent::ShowNormalWidget should be shown normally (obsolete).
QEvent::ShowToParentA child widget has been shown.
QEvent::ShowWindowRequestWidget's window should be shown (obsolete).
QEvent::SockActSocket activated, used to implement QSocketNotifier.
QEvent::SpeechReserved for speech input.
QEvent::StatusTip 
QEvent::StyleChangeWidget's style has been changed
QEvent::TabletMoveA Wacom Tablet Move Event.
QEvent::TabletPressA Wacom Tablet Press Event
QEvent::TabletReleaseA Wacom Tablet Release Event
QEvent::TimerRegular timer events, QTimerEvent.
QEvent::ToolBarSwitchThe toolbar button is toggled on Mac.
QEvent::ToolTip 
QEvent::UpdateRequestThe widget should be repainted.
QEvent::WhatsThis 
QEvent::WhatsThisClicked 
QEvent::WheelMouse wheel rolled, QWheelEvent.
QEvent::WindowActivateWindow was activated.
QEvent::WindowBlocked 
QEvent::WindowDeactivateWindow was deactivated.
QEvent::WindowIconChange 
QEvent::WindowStateChangeThe window's state, i.e. minimized, maximized or full-screen, has changed. See QWidget::windowState().
QEvent::WindowTitleChange 
QEvent::WindowUnblocked 
QEvent::UserUser-defined event.
QEvent::MaxUserLast user event id.

User events should have values between User and MaxUser inclusive.


Property Documentation

accepted : bool

the accept flag of the event object

Setting the accept parameter indicates that the event receiver wants the event. Unwanted events might be propagated to the parent widget. By default, isAccepted() is set to true, but don't rely on this as subclasses may choose to clear it in their constructor.

For convenience, the accept flag can also be set with accept(), and cleared with ignore().

Access functions:


Member Function Documentation

QEvent::QEvent ( Type type )

Contructs an event object of type type.

QEvent::~QEvent ()   [virtual]

Destroys the event. If it was posted, it will be removed from the list of events to be posted.

void QEvent::accept ()

Sets the accept flag of the event object, the equivalent of callign setAccepted(true).

Setting the accept parameter indicates that the event receiver wants the event. Unwanted events might be propagated to the parent widget.

See also ignore().

void QEvent::ignore ()

Clears the accept flag parameter of the event object, the equivalent of calling setAccepted(false).

Clearing the accept parameter indicates that the event receiver does not want the event. Unwanted events might be propgated to the parent widget.

See also accept().

bool QEvent::spontaneous () const

Returns true if the event originated outside the application (a system event); otherwise returns false.

Type QEvent::type () const

Returns the event type.


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Qt 4.0.0-b1