QT中event事件机制与signal关系

事件处理流程：

某个事件发生------>exec()循环会接收到这个事件------>

创建一个事件对象，并将对象传递给QObject::event()------>

在QWidget::event()函数中，分配给特定的事件处理函数------>

在QButton的事件处理函数中emit(clicked消息)

signal发送的方式：emit

event发送的方式：

1：窗口系统事件；（QEvent::Type中列出的）

2：由sendEvent()/postEvent()手动发送；

event与signal的关系：

两者没有必然的关系。只是有些事件发生时，在事件处理函数中会调用emit发送一个信号。

bool QObject::event( QEvent *e )

{

#if defined(CHECK_NULL)

if ( e == 0 )

qWarning( "QObject::event: Null events are not permitted" );

#endif

if ( eventFilters ) { // try filters

if ( activate_filters(e) ) // stopped by a filter

return TRUE;

}

switch ( e->type() ) {

case QEvent::Timer:

timerEvent( (QTimerEvent*)e );

return TRUE;

case QEvent::ChildInserted: case QEvent::ChildRemoved:

childEvent( (QChildEvent*)e );

return TRUE;

default:

break;

}

return FALSE;

}

//QObject::event()在QWidget中被重新实现。

bool QWidget::event( QEvent *e )

{

if ( QObject::event( e ) )

return TRUE;

switch ( e->type() ) {

case QEvent::MouseMove:

mouseMoveEvent( (QMouseEvent*)e );

break;

case QEvent::MouseButtonPress:

mousePressEvent( (QMouseEvent*)e );

break;

case QEvent::MouseButtonRelease:

mouseReleaseEvent( (QMouseEvent*)e );

break;

case QEvent::MouseButtonDblClick:

mouseDoubleClickEvent( (QMouseEvent*)e );

break;

case QEvent::Wheel:

wheelEvent( (QWheelEvent*)e );

if ( ! ((QWheelEvent*)e)->isAccepted() )

return FALSE;

break;

case QEvent::KeyPress: {

QKeyEvent *k = (QKeyEvent *)e;

bool res = FALSE;

if ( k->key() == Key_Backtab ||

(k->key() == Key_Tab &&

(k->state() & ShiftButton)) ) {

QFocusEvent::setReason( QFocusEvent::Tab );

res = focusNextPrevChild( FALSE );

QFocusEvent::resetReason();

} else if ( k->key() == Key_Tab ) {

QFocusEvent::setReason( QFocusEvent::Tab );

res = focusNextPrevChild( TRUE );

QFocusEvent::resetReason();

}

if ( res )

break;

QWidget *w = this;

while ( w ) {

w->keyPressEvent( k );

if ( k->isAccepted() || w->isTopLevel() )

break;

w = w->parentWidget();

k->accept();

}

}

break;

case QEvent::KeyRelease: {

QKeyEvent *k = (QKeyEvent *)e;

QWidget *w = this;

while ( w ) {

k->accept();

w->keyReleaseEvent( k );

if ( k->isAccepted() || w->isTopLevel() )

break;

w = w->parentWidget();

}

}

break;

case QEvent::FocusIn:

setFontSys();

focusInEvent( (QFocusEvent*)e );

break;

case QEvent::FocusOut:

focusOutEvent( (QFocusEvent*)e );

break;

case QEvent::Enter:

enterEvent( e );

break;

case QEvent::Leave:

leaveEvent( e );

break;

case QEvent::Paint:

// At this point the event has to be delivered, regardless

// whether the widget isVisible() or not because it

// already went through the filters

paintEvent( (QPaintEvent*)e );

break;

case QEvent::Move:

moveEvent( (QMoveEvent*)e );

break;

case QEvent::Resize:

resizeEvent( (QResizeEvent*)e );

break;

case QEvent::Close: {

QCloseEvent *c = (QCloseEvent *)e;

closeEvent( c );

if ( !c->isAccepted() )

return FALSE;

}

break;

#ifndef QT_NO_DRAGANDDROP

case QEvent::Drop:

dropEvent( (QDropEvent*) e);

break;

case QEvent::DragEnter:

dragEnterEvent( (QDragEnterEvent*) e);

break;

case QEvent::DragMove:

dragMoveEvent( (QDragMoveEvent*) e);

break;

case QEvent::DragLeave:

dragLeaveEvent( (QDragLeaveEvent*) e);

break;

#endif

case QEvent::Show:

showEvent( (QShowEvent*) e);

break;

case QEvent::Hide:

hideEvent( (QHideEvent*) e);

break;

case QEvent::ShowWindowRequest:

if ( !isHidden() )

showWindow();

break;

case QEvent::ParentFontChange:

if ( isTopLevel() )

break;

// FALL THROUGH

case QEvent::ApplicationFontChange:

if ( !own_font && !isDesktop() ) {

if ( !isTopLevel() && QApplication::font( this ).isCopyOf( QApplication::font() ) )

setFont( parentWidget()->font() );

else

setFont( QApplication::font( this ) );

own_font = FALSE;

}

break;

#ifndef QT_NO_PALETTE

case QEvent::ParentPaletteChange:

if ( isTopLevel() )

break;

// FALL THROUGH

case QEvent::ApplicationPaletteChange:

if ( !own_palette && !isDesktop() ) {

if ( !isTopLevel() && parentWidget() && QApplication::palette( this ).isCopyOf( QApplication::palette() ) )

setPalette( parentWidget()->palette() );

else

setPalette( QApplication::palette( this ) );

own_palette = FALSE;

}

break;

#endif

default:

if ( e->type() >= QEvent::User ) {

customEvent( (QCustomEvent*) e );

return TRUE;

}

return FALSE;

}

return TRUE;

}

void QButton::keyPressEvent( QKeyEvent *e )

{

switch ( e->key() ) {

case Key_Enter:

case Key_Return:

if ( inherits("QPushButton") )

emit clicked();

else

e->ignore();

break;

case Key_Space:

if ( !e->isAutoRepeat() ) {

if ( got_a_release )

setDown( TRUE );

else {

buttonDown = TRUE;

repaint( FALSE );

}

if ( inherits("QPushButton") )

emit pressed();

else

e->ignore();

}

break;

case Key_Up:

case Key_Left:

#ifndef QT_NO_BUTTONGROUP

if ( group() )

group()->moveFocus( e->key() );

else

#endif

focusNextPrevChild( FALSE );

break;

case Key_Right:

case Key_Down:

#ifndef QT_NO_BUTTONGROUP

if ( group() )

group()->moveFocus( e->key() );

else

#endif

focusNextPrevChild( TRUE );

break;

case Key_Escape:

if ( buttonDown ) {

buttonDown = FALSE;

update();

break;

}

// fall through

default:

e->ignore();

}

}