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[轉(zhuǎn)]淺議Qt的事件處理機(jī)制二

淺議Qt的事件處理機(jī)制二
我們在上文中，介紹了Qt框架的事件處理機(jī)制：事件的產(chǎn)生、分發(fā)、接受和處理，并以視窗系統(tǒng)鼠標(biāo)點(diǎn)擊QWidget為例，對代碼進(jìn)行了剖析，向大家分析了Qt框架如何通過Event Loop處理進(jìn)入處理消息隊(duì)列循環(huán)，如何一步一步委派給平臺相關(guān)的函數(shù)獲取、打包用戶輸入事件交給視窗系統(tǒng)處理，函數(shù)調(diào)用棧如下：

QtCored4.dll!QEventDispatcherWin32::processEvents()  qeventdispatcher_win.cpp Line 742    C++
QtGuid4.dll!QGuiEventDispatcherWin32::processEvents()  Line 1202 + 0x15 bytes    C++
QtCored4.dll!QEventLoop::processEvents()  Line 150    C++
QtCored4.dll!QEventLoop::exec()  Line 204 + 0x2d bytes    C++
QtCored4.dll!QCoreApplication::exec()  Line 1187 + 0x15 bytes    C++
QtGuid4.dll!QApplication::exec()  Line 3813    C++
qt03.exe!main()  Line 11 + 0x6 bytes    C++
qt03.exe!WinMain()  Line 131 + 0x12 bytes    C++
qt03.exe!__tmainCRTStartup()  Line 574 + 0x35 bytes    C
qt03.exe!WinMainCRTStartup()  Line 399    C
kernel32.dll!_BaseProcessStart@4()  + 0x23 bytes



1.main(int, char **)
2.QApplication::exec()
3.QCoreApplication::exec()
4.QEventLoop::exec(ProcessEventsFlags )
5.QEventLoop::processEvents(ProcessEventsFlags )
6.QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags)

本文將介紹Qt app在視窗系統(tǒng)回調(diào)后，事件又是怎么一步步通過QApplication分發(fā)給最終事件的接受和處理者QWidget::event, （QWidget繼承Object,重載其虛函數(shù)event)，以下所有的討論都將嵌入在源碼之中。

1.QT_WIN_CALLBACK QtWndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) bool QETWidget::translateMouseEvent(const MSG &msg)
2.bool QApplicationPrivate::sendMouseEvent(

)
3.inline bool QCoreApplication::sendSpontaneousEvent(QObject *receiver, QEvent *event)
4.bool QCoreApplication::notifyInternal(QObject *receiver, QEvent *event)
5.bool QApplication::notify(QObject *receiver, QEvent *e)
6.bool QApplicationPrivate::notify_helper(QObject *receiver, QEvent * e)
7.bool QWidget::event(QEvent *event)

// (續(xù)上文Section 7) Section 2-1：
QT_WIN_CALLBACK QtWndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{

   //檢查message是否屬于Qt可轉(zhuǎn)義的鼠標(biāo)事件
   if (qt_is_translatable_mouse_event(message)) {
        if (QApplication::activePopupWidget() != 0) {
            POINT curPos = msg.pt;
            //取得鼠標(biāo)點(diǎn)擊坐標(biāo)所在的QWidget指針，它指向我們在main創(chuàng)建的widget實(shí)例
            QWidget* w = QApplication::widgetAt(curPos.x, curPos.y);
            if (w)
                widget = (QETWidget*)w;
        }
        if (!qt_tabletChokeMouse) {
            //對，就在這里。Windows的回調(diào)函數(shù)將鼠標(biāo)事件分發(fā)回給了Qt Widget
            // => Section 2-2
            result = widget->translateMouseEvent(msg);

        }
    }
}
// Section 2-2  $QTDIR/src/gui/kernel/qapplication_win.cpp
//該函數(shù)所在與Windows平臺相關(guān)，主要職責(zé)就是把已windows格式打包的鼠標(biāo)事件解包、翻譯成QApplication可識別的QMouseEvent,QWidget.
//打包翻譯成功return true,否則false

bool QETWidget::translateMouseEvent(const MSG &msg)
{
    //.. 這里很長的代碼給以忽略


    //比如主窗口中有一個QPushButton,當(dāng)在PushButton單擊時,translateMouseEvent函數(shù)會計(jì)算出當(dāng)前單擊事件所在的的控件alienWidget,然后通過sendMouseEvent發(fā)送給當(dāng)前到alienWidget!

    //單擊事件,計(jì)算出當(dāng)前單擊事件所在的的控件alienWidget
    state  = translateButtonState(msg.wParam, type, button); // button state
    const QPoint widgetPos = mapFromGlobal(QPoint(msg.pt.x, msg.pt.y));
    QWidget *alienWidget = !internalWinId() ? this : childAt(widgetPos);


    //計(jì)算是否符合MouseButtonPress條件
    gpos = msg.pt;
    pos = mapFromGlobal(QPoint(gpos.x, gpos.y));

    // mouse button pressed
    if (!qt_button_down && (type == QEvent::MouseButtonPress || type == QEvent::MouseButtonDblClick)) {
        QWidget *tlw = window();
        if (QWidget *child = tlw->childAt(mapTo(tlw, pos)))
            qt_button_down = child;
        else
            qt_button_down = this;
    }

    if (alienWidget && alienWidget->internalWinId())
        alienWidget = 0;

    const QPoint globalPos(gpos.x,gpos.y);
    QWidget *widget = QApplicationPrivate::pickMouseReceiver(this, globalPos, pos, type,
                                                             Qt::MouseButtons(bs),
                                                             qt_button_down, alienWidget);
    if (!widget)
        return false; // don't send event

    QMouseEvent e(type, pos, globalPos, Qt::MouseButton(button),
                  Qt::MouseButtons(state & Qt::MouseButtonMask),
                  Qt::KeyboardModifiers(state & Qt::KeyboardModifierMask));


      // 讓我們看一下sendMouseEvent的聲明
     // widget是事件的接受者； e是封裝好的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)
{
     //至此與平臺相關(guān)代碼處理完畢
     //MouseEvent默認(rèn)的發(fā)送方式是spontaneous, 所以將執(zhí)行sendSpontaneousEvent。 sendSpontaneousEvent() 與 sendEvent的代碼實(shí)現(xiàn)幾乎相同，除了將QEvent的屬性spontaneous標(biāo)記不同。這里是解釋什么spontaneous事件：如果事件由應(yīng)用程序之外產(chǎn)生的，比如一個系統(tǒng)事件。顯然MousePress事件是由視窗系統(tǒng)產(chǎn)生的一個的事件（詳見上文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);
}
// (續(xù)上文Section 7) Section 2-1：
QT_WIN_CALLBACK QtWndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{

    //如果我們通過EventFilter QCoreApplication::setEventFilter (EventFilter filter )設(shè)置了EventFilter
    //將會調(diào)用我們設(shè)置的EventFilter
    // send through app filter
    if (qApp->filterEvent(&msg, &res))
        return res;

}
// Section 2-2  $QTDIR/src/gui/kernel/qapplication_win.cpp
//該函數(shù)所在與Windows平臺相關(guān)，主要職責(zé)就是把已windows格式打包的鼠標(biāo)事件解包、翻譯成QApplication可識別的QMouseEvent,QWidget.
bool QETWidget::translateMouseEvent(const MSG &msg)
{
     //.. 這里很長的代碼給以忽略
     // 讓我們看一下sendMouseEvent的聲明
     // widget是事件的接受者； e是封裝好的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)
{
     //至此與平臺相關(guān)代碼處理完畢
     //MouseEvent默認(rèn)的發(fā)送方式是spontaneous, 所以將執(zhí)行sendSpontaneousEvent。 sendSpontaneousEvent() 與 sendEvent的代碼實(shí)現(xiàn)幾乎相同，除了將QEvent的屬性spontaneous標(biāo)記不同。這里是解釋什么spontaneous事件：如果事件由應(yīng)用程序之外產(chǎn)生的，比如一個系統(tǒng)事件。顯然MousePress事件是由視窗系統(tǒng)產(chǎn)生的一個的事件（詳見上文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)
{
    //將event標(biāo)記為自發(fā)事件
     //進(jìn)一步調(diào)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)
{

    // 幾行代碼對于Qt Jambi (QT Java綁定版本）和QSA (QT Script for Application)的支持

     // 以下代碼主要意圖為Qt強(qiáng)制事件只能夠發(fā)送給當(dāng)前線程里的對象，也就是說receiver->d_func()->threadData應(yīng)該等于QThreadData::current()。注意，跨線程的事件需要借助Event Loop來派發(fā)
     QObjectPrivate *d = receiver->d_func();
    QThreadData *threadData = d->threadData;
    ++threadData->loopLevel;
    bool returnValue;
    QT_TRY {
        //哇，終于來到大名鼎鼎的函數(shù)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和它的重載函數(shù)QApplication::notify在Qt的派發(fā)過程中起到核心的作用，Qt的官方文檔時這樣說的：任何線程的任何對象的所有事件在發(fā)送時都會調(diào)用notify函數(shù)。
bool QApplication::notify(QObject *receiver, QEvent *e)
{
   //代碼很長，最主要的是一個大大的Switch,Case
   ..
   switch ( e->type())
   {

    case QEvent::MouseButtonPress:
    case QEvent::MouseButtonRelease:
    case QEvent::MouseButtonDblClick:
    case QEvent::MouseMove:

        //讓自己私有類(d是私有類的句柄）來進(jìn)一步處理 ==> 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)
{

    // 向事件過濾器發(fā)送該事件，這里介紹一下Event Filters. 事件過濾器是一個接受即將發(fā)送給目標(biāo)對象所有事件的對象。
   //如代碼所示它開始處理事件在目標(biāo)對象行動之前。過濾器的QObject::eventFilter（）實(shí)現(xiàn)被調(diào)用，能接受或者丟棄過濾，允許或者拒絕事件的更進(jìn)一步的處理。如果所有的事件過濾器允許更進(jìn)一步的事件處理，事件將被發(fā)送到目標(biāo)對象本身。如果他們中的一個停止處理，目標(biāo)和任何后來的事件過濾器不能看到任何事件。
    if (sendThroughObjectEventFilters(receiver, e))
        return true;
     // 遞交事件給receiver  => Section 2-8
    bool consumed = receiver->event(e);
    e->spont = false;
}
// Section 2-8  $QTDIR/gui/kernel/qwidget.cpp
// QApplication通過notify及其私有類notify_helper,將事件最終派發(fā)給了QObject的子類- 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.
        //mousePressEvent是虛函數(shù)，QWidget的子類可以通過重載重新定義mousePress事件的行為
        mousePressEvent((QMouseEvent*)event);
        break;
}

/*!
    Sends \a message through the event filter that was set by
    setEventFilter(). If no event filter has been set, this function
    returns false; otherwise, this function returns the result of the
    event filter function in the \a result parameter.
    \sa setEventFilter()
*/
bool QCoreApplication::filterEvent(void *message, long *result)
{
    Q_D(QCoreApplication);
    if (result)
        *result = 0;
    if (d->eventFilter)
        return d->eventFilter(message, result);
#ifdef Q_OS_WIN
    return winEventFilter(reinterpret_cast<MSG *>(message), result);
#else
    return false;
#endif
}

posted on 2013-07-04 12:00 天下閱讀(2561) 評論(0) 編輯收藏引用所屬分類: QT

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