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QEvent Class Reference
[QtCore module]

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

 #include <QEvent>

Inherited by QAccessibleEvent, QActionEvent, QChildEvent, QCloseEvent, QCustomEvent, QDragLeaveEvent, QDropEvent, QDynamicPropertyChangeEvent, QFileOpenEvent, QFocusEvent, QGraphicsSceneEvent, QHelpEvent, QHideEvent, QHoverEvent, QIconDragEvent, QInputEvent, QInputMethodEvent, QMoveEvent, QPaintEvent, QResizeEvent, QShortcutEvent, QShowEvent, QStatusTipEvent, QTimerEvent, QWhatsThisClickedEvent, and QWindowStateChangeEvent.

• List of all members, including inherited members

Public Types

• enum Type { None, AccessibilityDescription, AccessibilityHelp, AccessibilityPrepare, ..., MaxUser }

Properties

• accepted : bool

Public Functions

• QEvent ( Type type )
• virtual ~QEvent ()
• void accept ()
• void ignore ()
• bool isAccepted () const
• void setAccepted ( bool accepted )
• bool spontaneous () const
• Type type () const

Static Public Members

• int registerEventType ( int hint = -1 )

Detailed Description

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

Qt's main event loop (QCoreApplication::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 QCoreApplication::sendEvent() and QCoreApplication::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.

See also QObject::event(), QObject::installEventFilter(), QWidget::event(), QCoreApplication::sendEvent(), QCoreApplication::postEvent(), and QCoreApplication::processEvents().

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:

User events should have values between User and MaxUser:

For convenience, you can use the registerEventType() function to register and reserve a custom event type for your application. Doing so will allow you to avoid accidentally re-using a custom event type already in use elsewhere in your application.

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:

• bool isAccepted () const
• void setAccepted ( bool accepted )

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 calling 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().

int QEvent::registerEventType ( int hint = -1 )   [static]

Registers and returns a custom event type. The hint provided will be used if it is available, otherwise it will return a value between QEvent::User and QEvent::MaxUser that has not yet been registered. The hint is ignored if its value is not between QEvent::User and QEvent::MaxUser.

Note: This function is thread-safe.

This function was introduced in Qt 4.4.

bool QEvent::spontaneous () const

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

The return value of this function is not defined for paint events.

Type QEvent::type () const

Returns the event type.