qt 消息處理機制深入分析 (Qt消息機制與window程序消息的對比)

https://blog.csdn.net/liuzhezhe111/article/details/82154673

理解Qt消息機制刻不容緩，那我們從對比傳統的windows消息處理機制對比來說起；
只有知道QT底層的消息處理、對我們理解並學習Qt有很大幫助；
下面我將對windows程序與Qt對比，並在核心代碼處並給出注釋進行對比、方便學習。

注意重點看代碼中的注視進行對比：！

注意重點看代碼中的注視進行對比：！

注意重點看代碼中的注視進行對比：！

一：windows程序的消息處理
windows程序的處理大概一致
如下：
1.0 windows 消息處理機制：

    int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
            PSTR szCmdLine, int iCmdShow)
    {
        static TCHAR szAppName[] = TEXT("Hello");
        HWND   hwnd;
        MSG    msg;
        WNDCLASS wndclass;
        //fill wndclass
        wndclass.lpfnWndProc  = WndProc;
        ...
        RegisterClass(&wndclass);
        hwnd = CreateWindow( .... );      // creation parameters
        ShowWindow(hwnd, iCmdShow);
        UpdateWindow(hwnd);
        while(GetMessage(&msg, NULL, 0, 0))  { //這一塊位置得到消息
            TranslateMessage(&msg);//轉換消息
            DispatchMessage(&msg);//分發消息到系統處理
        }
        return msg.wParam;
    }

1.1 這是分發消息的回調函數熟悉windows程序應該不難看懂

    LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
    {
        HDC hdc;
        PAINTSTRUCT ps;
        RECT rect;
        switch(message) {
            case WM_CREATE:
                return 0;
            case WM_PAINT://重繪、比如窗口大小拉伸
                ...
                return 0;
            case WM_DESTROY:
                PostQuitMessage(0);
                return 0;
        }
        return DefWindowProc(hwnd, message, wParam, lParam); // windows 操作系統內部的消息機制、系統調用函數；
    }

二 Qt消息處理機制
2.0 Qt的消息機制


QEventDispatcherWin32：
注冊窗口類別，並創建一個隱藏窗口 （QEventDispatcherWin32_Internal_WidgetXXXX）
窗口的回調函數 qt_internal_proc()
安裝WH_GETMESSAGE類型的鈎子函數 qt_GetMessageHook()

    bool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags)
    if (!filterNativeEvent(QByteArrayLiteral("windows_generic_MSG"), &msg, 0))  與上面的消息循環：的while一樣 、得到過濾所有消息
    {
        TranslateMessage(&msg);//轉換消息
        DispatchMessage(&msg); //分發消息
    }

DispatchMessage(&msg); //分發消息
分發消息的或回調函數、這個與windows程序的CALLBACK WndProc一樣
LRESULT QT_WIN_CALLBACK qt_internal_proc(HWND hwnd, UINT message, WPARAM wp, LPARAM lp)
2.1 下面就是從系統獲得的消息后Qt封裝消息后所作的事情

這個就是Qt的消息回調：

    LRESULT QT_WIN_CALLBACK qt_internal_proc(HWND hwnd, UINT message, WPARAM wp, LPARAM lp)
    {
        if (message == WM_NCCREATE)
            return true;
        // MSG windows 消息結構：
        MSG msg;
        msg.hwnd = hwnd;
        msg.message = message;
        msg.wParam = wp;
        msg.lParam = lp;
        QAbstractEventDispatcher* dispatcher = QAbstractEventDispatcher::instance();
        long result;
        if (!dispatcher) {
            if (message == WM_TIMER)
                KillTimer(hwnd, wp);
            return 0;
        } else if (dispatcher->filterNativeEvent(QByteArrayLiteral("windows_dispatcher_MSG"), &msg, &result)) {
            return result;
        }
     
    #ifdef GWLP_USERDATA
        QEventDispatcherWin32 *q = (QEventDispatcherWin32 *) GetWindowLongPtr(hwnd, GWLP_USERDATA);
    #else
        QEventDispatcherWin32 *q = (QEventDispatcherWin32 *) GetWindowLong(hwnd, GWL_USERDATA);
    #endif
        QEventDispatcherWin32Private *d = 0;
        if (q != 0)
            d = q->d_func();
        // 下面 WM_QT_SOCKETNOTIFIER socket Qt 事件底層的處理機制、處理網絡的消息事件
        if (message == WM_QT_SOCKETNOTIFIER) {
            // socket notifier message
            int type = -1;
            switch (WSAGETSELECTEVENT(lp)) { //在非阻塞模式下利用socket事件的消息機制，Server端與Client端之間的通信處於異步狀態下
            case FD_READ: //socket 文件描述符 read 、有數據到達時發生
            case FD_ACCEPT: //socket 文件描述符 接收連接 、 作為客戶端連接成功時發生
                type = 0;
                break;
            case FD_WRITE: //socket 文件描述符寫 、有數據發送時產生
            case FD_CONNECT:  //socket 文件描述符發起連接 、 作為服務端等待連接成功時發生    
                type = 1;
                break;
            case FD_OOB: //socket 文件描述符收到數據 、 收到外帶數據時發生
                type = 2;
                break;
            case FD_CLOSE: //socket 文件描述符關閉斷開連接 、套接口關閉時發生
                type = 3;
                break;
            }
            if (type >= 0) {
                Q_ASSERT(d != 0);
                QSNDict *sn_vec[4] = { &d->sn_read, &d->sn_write, &d->sn_except, &d->sn_read };
                QSNDict *dict = sn_vec[type];
     
                QSockNot *sn = dict ? dict->value(wp) : 0;
                if (sn == nullptr) {
                    d->postActivateSocketNotifiers();
                } else {
                    Q_ASSERT(d->active_fd.contains(sn->fd));
                    QSockFd &sd = d->active_fd[sn->fd];
                    if (sd.selected) {
                        Q_ASSERT(sd.mask == 0);
                        d->doWsaAsyncSelect(sn->fd, 0);
                        sd.selected = false;
                    }
                    d->postActivateSocketNotifiers();
     
                    // Ignore the message if a notification with the same type was
                    // received previously. Suppressed message is definitely spurious.
                    const long eventCode = WSAGETSELECTEVENT(lp);
                    if ((sd.mask & eventCode) != eventCode) {
                        sd.mask |= eventCode;
                        QEvent event(type < 3 ? QEvent::SockAct : QEvent::SockClose);
                        QCoreApplication::sendEvent(sn->obj, &event);
                    }
                }
            }
            return 0;
        } else if (message == WM_QT_ACTIVATENOTIFIERS) { // 處理postEvent事件
            Q_ASSERT(d != 0);
            // postEvent() 事件，因為是隊列的存儲的方式，郵遞發送消息、直接返回
            
            // Postpone activation if we have unhandled socket notifier messages
            // in the queue. WM_QT_ACTIVATENOTIFIERS will be posted again as a result of
            // event processing.
            MSG msg;//異步調用
            if (!PeekMessage(&msg, d->internalHwnd,
                             WM_QT_SOCKETNOTIFIER, WM_QT_SOCKETNOTIFIER, PM_NOREMOVE)
                && d->queuedSocketEvents.isEmpty()) { // d->queuedSocketEvents 消息隊列如果消息有很多的時候都會加入這個隊列、這個就是關於Qt::connect();參數：地址
                // register all socket notifiers
                for (QSFDict::iterator it = d->active_fd.begin(), end = d->active_fd.end();
                     it != end; ++it) {
                    QSockFd &sd = it.value();
                    if (!sd.selected) {
                        d->doWsaAsyncSelect(it.key(), sd.event);
                        // allow any event to be accepted
                        sd.mask = 0;
                        sd.selected = true;
                    }
                }
            }
            d->activateNotifiersPosted = false;
            return 0;
        } else if (message == WM_QT_SENDPOSTEDEVENTS  // 處理 Qt sendPostEvent()發送事件
                   // we also use a Windows timer to send posted events when the message queue is full
                   // WM_QT_SENDPOSTEDEVENTS : 這個消息是我們Qt程序大部分走的事件，特殊情況除外。
                   || (message == WM_TIMER
                       && d->sendPostedEventsWindowsTimerId != 0
                       && wp == (uint)d->sendPostedEventsWindowsTimerId)) {
            const int localSerialNumber = d->serialNumber.load();
            if (localSerialNumber != d->lastSerialNumber) {
                d->lastSerialNumber = localSerialNumber;
                q->sendPostedEvents();//因為sendevent是同步所以直接進入進行調用
            }
            return 0;
        } else if (message == WM_TIMER) {//系統定時器超時
            Q_ASSERT(d != 0);
            d->sendTimerEvent(wp);
            return 0;
        }
     
        return DefWindowProc(hwnd, message, wp, lp); // 這個與windows程序一樣的地方。
    }

另外還有一點很重要的：大家都知道Qt消息處理比windows處理的塊，Qt程序通過一通處理才調用DefWindowProc傳給系統所以Qt系統的消息機制是比windows的消息慢的原因之一；
不過他也有它優點：qt的信號與槽函數讓我們讓我們編程更方便。
2.3 消息全局通知事件

另外我們都知道我們開發的系統、所有的消息都會到這個類QApplication::notify事件過濾所有的事件：
其實QApplication繼承QGuiApplication類；

    bool QGuiApplication::notify(QObject *object, QEvent *event)
    {
        if (object->isWindowType())
            QGuiApplicationPrivate::sendQWindowEventToQPlatformWindow(static_cast<QWindow *>(object), event);
        return QCoreApplication::notify(object, event);
    }

2.4 消息的組裝

下面是所有的消息類型處理：在我們開發的系統中別人使用processEvent發送消息是比較高效的。
原因：這個消息直達經過的處理的少。

    void QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent *e)
    {
        switch(e->type) {
        case QWindowSystemInterfacePrivate::FrameStrutMouse:
        case QWindowSystemInterfacePrivate::Mouse:
            QGuiApplicationPrivate::processMouseEvent(static_cast<QWindowSystemInterfacePrivate::MouseEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::Wheel:
            QGuiApplicationPrivate::processWheelEvent(static_cast<QWindowSystemInterfacePrivate::WheelEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::Key:
            QGuiApplicationPrivate::processKeyEvent(static_cast<QWindowSystemInterfacePrivate::KeyEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::Touch:
            QGuiApplicationPrivate::processTouchEvent(static_cast<QWindowSystemInterfacePrivate::TouchEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::GeometryChange:
            QGuiApplicationPrivate::processGeometryChangeEvent(static_cast<QWindowSystemInterfacePrivate::GeometryChangeEvent*>(e));
            break;
        case QWindowSystemInterfacePrivate::Enter:
            QGuiApplicationPrivate::processEnterEvent(static_cast<QWindowSystemInterfacePrivate::EnterEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::Leave:
            QGuiApplicationPrivate::processLeaveEvent(static_cast<QWindowSystemInterfacePrivate::LeaveEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::ActivatedWindow:
            QGuiApplicationPrivate::processActivatedEvent(static_cast<QWindowSystemInterfacePrivate::ActivatedWindowEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::WindowStateChanged:
            QGuiApplicationPrivate::processWindowStateChangedEvent(static_cast<QWindowSystemInterfacePrivate::WindowStateChangedEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::WindowScreenChanged:
            QGuiApplicationPrivate::processWindowScreenChangedEvent(static_cast<QWindowSystemInterfacePrivate::WindowScreenChangedEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::ApplicationStateChanged: {
            QWindowSystemInterfacePrivate::ApplicationStateChangedEvent * changeEvent = static_cast<QWindowSystemInterfacePrivate::ApplicationStateChangedEvent *>(e);
            QGuiApplicationPrivate::setApplicationState(changeEvent->newState, changeEvent->forcePropagate); }
            break;
        case QWindowSystemInterfacePrivate::FlushEvents: {
            QWindowSystemInterfacePrivate::FlushEventsEvent *flushEventsEvent = static_cast<QWindowSystemInterfacePrivate::FlushEventsEvent *>(e);
            QWindowSystemInterface::deferredFlushWindowSystemEvents(flushEventsEvent->flags); }
            break;
        case QWindowSystemInterfacePrivate::Close:
            QGuiApplicationPrivate::processCloseEvent(
                    static_cast<QWindowSystemInterfacePrivate::CloseEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::ScreenOrientation:
            QGuiApplicationPrivate::reportScreenOrientationChange(
                    static_cast<QWindowSystemInterfacePrivate::ScreenOrientationEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::ScreenGeometry:
            QGuiApplicationPrivate::reportGeometryChange(
                    static_cast<QWindowSystemInterfacePrivate::ScreenGeometryEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::ScreenLogicalDotsPerInch:
            QGuiApplicationPrivate::reportLogicalDotsPerInchChange(
                    static_cast<QWindowSystemInterfacePrivate::ScreenLogicalDotsPerInchEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::ScreenRefreshRate:
            QGuiApplicationPrivate::reportRefreshRateChange(
                    static_cast<QWindowSystemInterfacePrivate::ScreenRefreshRateEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::ThemeChange:
            QGuiApplicationPrivate::processThemeChanged(
                        static_cast<QWindowSystemInterfacePrivate::ThemeChangeEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::Expose:
            QGuiApplicationPrivate::processExposeEvent(static_cast<QWindowSystemInterfacePrivate::ExposeEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::Tablet:
            QGuiApplicationPrivate::processTabletEvent(
                        static_cast<QWindowSystemInterfacePrivate::TabletEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::TabletEnterProximity:
            QGuiApplicationPrivate::processTabletEnterProximityEvent(
                        static_cast<QWindowSystemInterfacePrivate::TabletEnterProximityEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::TabletLeaveProximity:
            QGuiApplicationPrivate::processTabletLeaveProximityEvent(
                        static_cast<QWindowSystemInterfacePrivate::TabletLeaveProximityEvent *>(e));
            break;
    #ifndef QT_NO_GESTURES
        case QWindowSystemInterfacePrivate::Gesture:
            QGuiApplicationPrivate::processGestureEvent(
                        static_cast<QWindowSystemInterfacePrivate::GestureEvent *>(e));
            break;
    #endif
        case QWindowSystemInterfacePrivate::PlatformPanel:
            QGuiApplicationPrivate::processPlatformPanelEvent(
                        static_cast<QWindowSystemInterfacePrivate::PlatformPanelEvent *>(e));
            break;
        case QWindowSystemInterfacePrivate::FileOpen:
            QGuiApplicationPrivate::processFileOpenEvent(
                        static_cast<QWindowSystemInterfacePrivate::FileOpenEvent *>(e));
            break;
    #ifndef QT_NO_CONTEXTMENU
            case QWindowSystemInterfacePrivate::ContextMenu:
            QGuiApplicationPrivate::processContextMenuEvent(
                        static_cast<QWindowSystemInterfacePrivate::ContextMenuEvent *>(e));
            break;
    #endif
        case QWindowSystemInterfacePrivate::EnterWhatsThisMode:
            QGuiApplication::postEvent(QGuiApplication::instance(), new QEvent(QEvent::EnterWhatsThisMode));
            break;
        default:
            qWarning() << "Unknown user input event type:" << e->type;
            break;
        }
    }

2.5 常用的消息過濾事件

通過2.4組裝的消息最終到達、此處。經過這些之后:之前的windows消息現在都已映射為QT類型的消息、進入Qt消息處理機制中來、才有了我們的消息過濾等等消息事件鍵盤鼠標等等；

    virtual void mouseDoubleClickEvent(QMouseEvent *event)
    virtual void mouseMoveEvent(QMouseEvent *event)
    virtual void mousePressEvent(QMouseEvent *event)
    virtual void mouseReleaseEvent(QMouseEvent *event)
    virtual void moveEvent(QMoveEvent *event)
    virtual bool nativeEvent(const QByteArray &eventType, void *message, long *result)
    virtual void paintEvent(QPaintEvent *event)
    virtual void resizeEvent(QResizeEvent *event)
    virtual void showEvent(QShowEvent *event)
    virtual void tabletEvent(QTabletEvent *event)
    virtual void wheelEvent(QWheelEvent *event)

重新實現上面的消息事件做我們的功能；

總結：

通過windows消息的運行機制與Qt的消息機制進行了對比。其實Qt在windows平台上的消息傳遞依賴的是windows消息機制。只不過在開始時進行注冊消息攔截等一些封裝處理、加工成Qt消息在Qt程序中進行傳遞。