- main(int, char **)
- QApplication::exec()
- QCoreApplication::exec()
- QEventLoop::exec(ProcessEventsFlags )
- QEventLoop::processEvents(ProcessEventsFlags )
- QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags)
本文将介绍Qt app在视窗系统回调后,事件又是怎么一步步通过QApplication分发给最终事件的接受和处理者QWidget::event, (QWidget继承Object,重载其虚函数event),以下所有的讨论都将嵌入在源码之中。
- QT_WIN_CALLBACK QtWndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) bool QETWidget::translateMouseEvent(const MSG &msg)
- bool QApplicationPrivate::sendMouseEvent(...)
- inline bool QCoreApplication::sendSpontaneousEvent(QObject *receiver, QEvent *event)
- bool QCoreApplication::notifyInternal(QObject *receiver, QEvent *event)
- bool QApplication::notify(QObject *receiver, QEvent *e)
- bool QApplicationPrivate::notify_helper(QObject *receiver, QEvent * e)
- bool QWidget::event(QEvent *event)
- // (续上文Section 7) Section 2-1:
- QT_WIN_CALLBACK QtWndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
- {
- ...
- //检查message是否属于Qt可转义的鼠标事件
- if (qt_is_translatable_mouse_event(message)) {
- if (QApplication::activePopupWidget() != 0) {
- POINT curPos = msg.pt;
- //取得鼠标点击坐标所在的QWidget指针,它指向我们在main创建的widget实例
- QWidget* w = QApplication::widgetAt(curPos.x, curPos.y);
- if (w)
- widget = (QETWidget*)w;
- }
- if (!qt_tabletChokeMouse) {
- //对,就在这里。Windows的回调函数将鼠标事件分发回给了Qt Widget
- // => Section 2-2
- result = widget->translateMouseEvent(msg);
- ...
- }
- // Section 2-2 $QTDIR\src\gui\kernel\qapplication_win.cpp
- //该函数所在与Windows平台相关,主要职责就是把已windows格式打包的鼠标事件解包、翻译成QApplication可识别的QMouseEvent,QWidget.
- bool QETWidget::translateMouseEvent(const MSG &msg)
- {
- //.. 这里很长的代码给以忽略
- // 让我们看一下sendMouseEvent的声明
- // widget是事件的接受者; e是封装好的QMouseEvent
- // ==> Section 2-3
- res = QApplicationPrivate::sendMouseEvent(widget, &e, alienWidget, this, &qt_button_down, qt_last_mouse_receiver);
- }
- // Section 2-3 $QTDIR\src\gui\kernel\qapplication.cpp
- bool QApplicationPrivate::sendMouseEvent(QWidget *receiver, QMouseEvent *event,
- QWidget *alienWidget, QWidget *nativeWidget,
- QWidget **buttonDown, QPointer<QWidget> &lastMouseReceiver,
- bool spontaneous)
- {
- //至此与平台相关代码处理完毕
- //MouseEvent默认的发送方式是spontaneous, 所以将执行sendSpontaneousEvent。 sendSpontaneousEvent() 与 sendEvent的代码实现几乎相同,
- 除了将QEvent的属性spontaneous标记不同。 这里是解释什么spontaneous事件:如果事件由应用程序之外产生的,比如一个系统事件。
- 显然MousePress事件是由视窗系统产生的一个的事件(详见上文Section 1~ Section 7),因此它是 spontaneous事件
- if (spontaneous)
- result = QApplication::sendSpontaneousEvent(receiver, event); ==〉Section 2-4
- else
- result = QApplication::sendEvent(receiver, event);
- }
- // Section 2-4 C:\Qt\4.7.1-Vs\src\corelib\kernel\qcoreapplication.h
- inline bool QCoreApplication::sendSpontaneousEvent(QObject *receiver, QEvent *event)
- {
- //将event标记为自发事件
- //进一步调用 2-5 QCoreApplication::notifyInternal
- if (event) event->spont = true; return self ? self->notifyInternal(receiver, event) : false;
- }
- // Section 2-5: $QTDIR\gui\kernel\qapplication.cpp
- bool QCoreApplication::notifyInternal(QObject *receiver, QEvent *event)
- {
- // 几行代码对于Qt Jambi (QT Java绑定版本) 和QSA (QT Script for Application)的支持
- ...
- // 以下代码主要意图为Qt强制事件只能够发送给当前线程里的对象,也就是说receiver->d_func()->threadData应该等于QThreadData::current()。
- 注意,跨线程的事件需要借助Event Loop来派发
- QObjectPrivate *d = receiver->d_func();
- QThreadData *threadData = d->threadData;
- ++threadData->loopLevel;
- bool returnValue;
- QT_TRY {
- //哇,终于来到大名鼎鼎的函数QCoreApplication::nofity()了 ==> Section 2-6
- returnValue = notify(receiver, event);
- } QT_CATCH (...) {
- --threadData->loopLevel;
- QT_RETHROW;
- }
- }
- // Section 2-6: $QTDIR\gui\kernel\qapplication.cpp
- // QCoreApplication::notify和它的重载函数QApplication::notify在Qt的派发过程中起到核心的作用,Qt的官方文档时这样说的:
- 任何线程的任何对象的所有事件在发送时都会调用notify函数。
- bool QApplication::notify(QObject *receiver, QEvent *e)
- {
- //代码很长,最主要的是一个大大的Switch,Case
- ..
- switch ( e->type())
- {
- ...
- case QEvent::MouseButtonPress:
- case QEvent::MouseButtonRelease:
- case QEvent::MouseButtonDblClick:
- case QEvent::MouseMove:
- ...
- //让自己私有类(d是私有类的句柄)来进一步处理 ==> Section 2-7
- res = d->notify_helper(w, w == receiver ? mouse : &me);
- e->spont = false;
- break;
- }
- ...
- }
- // Section 2-7: $QTDIR\gui\kernel\qapplication.cpp
- bool QApplicationPrivate::notify_helper(QObject *receiver, QEvent * e)
- {
- ...
- // 向事件过滤器发送该事件,这里介绍一下Event Filters. 事件过滤器是一个接受即将发送给目标对象所有事件的对象。
- //如代码所示它开始处理事件在目标对象行动之前。过滤器的QObject::eventFilter()实现被调用,能接受或者丢弃过滤,
- 允许或者拒绝事件的更进一步的处理。如果所有的事件过滤器允许更进一步的事件处理,事件将被发送到目标对象本身。
- 如果他们中的一个停止处理,目标和任何后来的事件过滤器不能看到任何事件。
- if (sendThroughObjectEventFilters(receiver, e))
- return true;
- // 递交事件给receiver => Section 2-8
- bool consumed = receiver->event(e);
- e->spont = false;
- }
- // Section 2-8 $QTDIR\gui\kernel\qwidget.cpp
- // QApplication通过notify及其私有类notify_helper,将事件最终派发给了QObject的子类- QWidget.
- bool QWidget::event(QEvent *event)
- {
- ...
- switch(event->type()) {
- case QEvent::MouseButtonPress:
- // Don't reset input context here. Whether reset or not is
- // a responsibility of input method. reset() will be
- // called by mouseHandler() of input method if necessary
- // via mousePressEvent() of text widgets.
- #if 0
- resetInputContext();
- #endif
- //mousePressEvent是虚函数,QWidget的子类可以通过重载重新定义mousePress事件的行为
- mousePressEvent((QMouseEvent*)event);
- break;
- }