qt 消息处理机制深入分析 (Qt消息机制与window程序消息的对比)

理解Qt消息机制刻不容缓，那我们从对比传统的windows消息处理机制对比来说起；
只有知道QT底层的消息处理、对我们理解并学习Qt有很大帮助；
下面我将对windows程序与Qt对比，并在核心代码处并给出注释进行对比、方便学习。

注意重点看代码中的注视进行对比：！

注意重点看代码中的注视进行对比：！

注意重点看代码中的注视进行对比：！


一：windows程序的消息处理 
windows程序的处理大概一致

如下：

1.0 windows 消息处理机制：

  1. int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
  2.         PSTR szCmdLine, int iCmdShow)
  3. {
  4.     static TCHAR szAppName[] = TEXT("Hello");
  5.     HWND   hwnd;
  6.     MSG    msg;
  7.     WNDCLASS wndclass;
  8.     //fill wndclass
  9.     wndclass.lpfnWndProc  = WndProc;
  10.     ...
  11.     RegisterClass(&wndclass);
  12.     hwnd = CreateWindow( .... );      // creation parameters
  13.     ShowWindow(hwnd, iCmdShow);
  14.     UpdateWindow(hwnd);
  15.     while(GetMessage(&msg, NULL, 0, 0))  { //这一块位置得到消息
  16.         TranslateMessage(&msg);//转换消息
  17.         DispatchMessage(&msg);//分发消息到系统处理
  18.     }
  19.     return msg.wParam;
  20. }

1.1 这是分发消息的回调函数熟悉windows程序应该不难看懂

  1. LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) 
  2. {
  3.     HDC hdc;
  4.     PAINTSTRUCT ps;
  5.     RECT rect;
  6.     switch(message) {
  7.         case WM_CREATE:
  8.             return 0;
  9.         case WM_PAINT://重绘、比如窗口大小拉伸
  10.             ...
  11.             return 0;
  12.         case WM_DESTROY:
  13.             PostQuitMessage(0);
  14.             return 0;
  15.     }
  16.     return DefWindowProc(hwnd, message, wParam, lParam); // windows 操作系统内部的消息机制、系统调用函数；
  17. }

二 Qt消息处理机制

2.0 Qt的消息机制


QEventDispatcherWin32：
注册窗口类别，并创建一个隐藏窗口 （QEventDispatcherWin32_Internal_WidgetXXXX）
窗口的回调函数 qt_internal_proc()
安装WH_GETMESSAGE类型的钩子函数 qt_GetMessageHook()

  1. bool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags) 
  2. if (!filterNativeEvent(QByteArrayLiteral("windows_generic_MSG"), &msg, 0))  与上面的消息循环：的while一样 、得到过滤所有消息
  3. {
  4. 	TranslateMessage(&msg);//转换消息
  5. 	DispatchMessage(&msg); //分发消息
  6. }

DispatchMessage(&msg); //分发消息
分发消息的或回调函数、这个与windows程序的CALLBACK WndProc一样
LRESULT QT_WIN_CALLBACK qt_internal_proc(HWND hwnd, UINT message, WPARAM wp, LPARAM lp)

2.1 下面就是从系统获得的消息后Qt封装消息后所作的事情

这个就是Qt的消息回调：

  1. LRESULT QT_WIN_CALLBACK qt_internal_proc(HWND hwnd, UINT message, WPARAM wp, LPARAM lp)
  2. {
  3.     if (message == WM_NCCREATE)
  4.         return true;
  5. 	// MSG windows 消息结构：
  6.     MSG msg;
  7.     msg.hwnd = hwnd;
  8.     msg.message = message;
  9.     msg.wParam = wp;
  10.     msg.lParam = lp;
  11.     QAbstractEventDispatcher* dispatcher = QAbstractEventDispatcher::instance();
  12.     long result;
  13.     if (!dispatcher) {
  14.         if (message == WM_TIMER)
  15.             KillTimer(hwnd, wp);
  16.         return 0;
  17.     } else if (dispatcher->filterNativeEvent(QByteArrayLiteral("windows_dispatcher_MSG"), &msg, &result)) {
  18.         return result;
  19.     }
  20.  
  21. #ifdef GWLP_USERDATA
  22.     QEventDispatcherWin32 *q = (QEventDispatcherWin32 *) GetWindowLongPtr(hwnd, GWLP_USERDATA);
  23. #else
  24.     QEventDispatcherWin32 *q = (QEventDispatcherWin32 *) GetWindowLong(hwnd, GWL_USERDATA);
  25. #endif
  26.     QEventDispatcherWin32Private *d = 0;
  27.     if (q != 0)
  28.         d = q->d_func();
  29. 	// 下面 WM_QT_SOCKETNOTIFIER socket Qt 事件底层的处理机制、处理网络的消息事件
  30.     if (message == WM_QT_SOCKETNOTIFIER) {
  31.         // socket notifier message
  32.         int type = -1;
  33.         switch (WSAGETSELECTEVENT(lp)) { //在非阻塞模式下利用socket事件的消息机制，Server端与Client端之间的通信处于异步状态下
  34.         case FD_READ: //socket 文件描述符 read 、有数据到达时发生
  35.         case FD_ACCEPT: //socket 文件描述符 接收连接 、 作为客户端连接成功时发生
  36.             type = 0;
  37.             break;
  38.         case FD_WRITE: //socket 文件描述符写 、有数据发送时产生
  39.         case FD_CONNECT:  //socket 文件描述符发起连接 、 作为服务端等待连接成功时发生	
  40.             type = 1;
  41.             break;
  42.         case FD_OOB: //socket 文件描述符收到数据 、 收到外带数据时发生
  43.             type = 2;
  44.             break;
  45.         case FD_CLOSE: //socket 文件描述符关闭断开连接 、套接口关闭时发生
  46.             type = 3;
  47.             break;
  48.         }
  49.         if (type >= 0) {
  50.             Q_ASSERT(d != 0);
  51.             QSNDict *sn_vec[4] = { &d->sn_read, &d->sn_write, &d->sn_except, &d->sn_read };
  52.             QSNDict *dict = sn_vec[type];
  53.  
  54.             QSockNot *sn = dict ? dict->value(wp) : 0;
  55.             if (sn == nullptr) {
  56.                 d->postActivateSocketNotifiers();
  57.             } else {
  58.                 Q_ASSERT(d->active_fd.contains(sn->fd));
  59.                 QSockFd &sd = d->active_fd[sn->fd];
  60.                 if (sd.selected) {
  61.                     Q_ASSERT(sd.mask == 0);
  62.                     d->doWsaAsyncSelect(sn->fd, 0);
  63.                     sd.selected = false;
  64.                 }
  65.                 d->postActivateSocketNotifiers();
  66.  
  67.                 // Ignore the message if a notification with the same type was
  68.                 // received previously. Suppressed message is definitely spurious.
  69.                 const long eventCode = WSAGETSELECTEVENT(lp);
  70.                 if ((sd.mask & eventCode) != eventCode) {
  71.                     sd.mask |= eventCode;
  72.                     QEvent event(type < 3 ? QEvent::SockAct : QEvent::SockClose);
  73.                     QCoreApplication::sendEvent(sn->obj, &event);
  74.                 }
  75.             }
  76.         }
  77.         return 0;
  78.     } else if (message == WM_QT_ACTIVATENOTIFIERS) { // 处理postEvent事件
  79.         Q_ASSERT(d != 0);
  80. 		// postEvent() 事件，因为是队列的存储的方式，邮递发送消息、直接返回
  81. 		
  82.         // Postpone activation if we have unhandled socket notifier messages
  83.         // in the queue. WM_QT_ACTIVATENOTIFIERS will be posted again as a result of
  84.         // event processing.
  85.         MSG msg;//异步调用
  86.         if (!PeekMessage(&msg, d->internalHwnd,
  87.                          WM_QT_SOCKETNOTIFIER, WM_QT_SOCKETNOTIFIER, PM_NOREMOVE)
  88.             && d->queuedSocketEvents.isEmpty()) { // d->queuedSocketEvents 消息队列如果消息有很多的时候都会加入这个队列、这个就是关于Qt::connect();参数：地址
  89.             // register all socket notifiers
  90.             for (QSFDict::iterator it = d->active_fd.begin(), end = d->active_fd.end();
  91.                  it != end; ++it) {
  92.                 QSockFd &sd = it.value();
  93.                 if (!sd.selected) {
  94.                     d->doWsaAsyncSelect(it.key(), sd.event);
  95.                     // allow any event to be accepted
  96.                     sd.mask = 0;
  97.                     sd.selected = true;
  98.                 }
  99.             }
  100.         }
  101.         d->activateNotifiersPosted = false;
  102.         return 0;
  103.     } else if (message == WM_QT_SENDPOSTEDEVENTS  // 处理 Qt sendPostEvent()发送事件
  104.                // we also use a Windows timer to send posted events when the message queue is full
  105. 			   // WM_QT_SENDPOSTEDEVENTS : 这个消息是我们Qt程序大部分走的事件，特殊情况除外。
  106.                || (message == WM_TIMER
  107.                    && d->sendPostedEventsWindowsTimerId != 0
  108.                    && wp == (uint)d->sendPostedEventsWindowsTimerId)) {
  109.         const int localSerialNumber = d->serialNumber.load();
  110.         if (localSerialNumber != d->lastSerialNumber) {
  111.             d->lastSerialNumber = localSerialNumber;
  112.             q->sendPostedEvents();//因为sendevent是同步所以直接进入进行调用
  113.         }
  114.         return 0;
  115.     } else if (message == WM_TIMER) {//系统定时器超时
  116.         Q_ASSERT(d != 0);
  117.         d->sendTimerEvent(wp);
  118.         return 0;
  119.     }
  120.  
  121.     return DefWindowProc(hwnd, message, wp, lp); // 这个与windows程序一样的地方。
  122. }

另外还有一点很重要的：大家都知道Qt消息处理比windows处理的块，Qt程序通过一通处理才调用DefWindowProc传给系统所以Qt系统的消息机制是比windows的消息慢的原因之一；
不过他也有它优点：qt的信号与槽函数让我们让我们编程更方便。

2.3 消息全局通知事件

另外我们都知道我们开发的系统、所有的消息都会到这个类QApplication::notify事件过滤所有的事件：
其实QApplication继承QGuiApplication类；

  1. bool QGuiApplication::notify(QObject *object, QEvent *event)
  2. {
  3.     if (object->isWindowType())
  4.         QGuiApplicationPrivate::sendQWindowEventToQPlatformWindow(static_cast(object), event);
  5.     return QCoreApplication::notify(object, event);
  6. }

2.4 消息的组装

下面是所有的消息类型处理：在我们开发的系统中别人使用processEvent发送消息是比较高效的。
原因：这个消息直达经过的处理的少。

  1. void QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent *e)
  2. {
  3.     switch(e->type) {
  4.     case QWindowSystemInterfacePrivate::FrameStrutMouse:
  5.     case QWindowSystemInterfacePrivate::Mouse:
  6.         QGuiApplicationPrivate::processMouseEvent(static_cast(e));
  7.         break;
  8.     case QWindowSystemInterfacePrivate::Wheel:
  9.         QGuiApplicationPrivate::processWheelEvent(static_cast(e));
  10.         break;
  11.     case QWindowSystemInterfacePrivate::Key:
  12.         QGuiApplicationPrivate::processKeyEvent(static_cast(e));
  13.         break;
  14.     case QWindowSystemInterfacePrivate::Touch:
  15.         QGuiApplicationPrivate::processTouchEvent(static_cast(e));
  16.         break;
  17.     case QWindowSystemInterfacePrivate::GeometryChange:
  18.         QGuiApplicationPrivate::processGeometryChangeEvent(static_cast(e));
  19.         break;
  20.     case QWindowSystemInterfacePrivate::Enter:
  21.         QGuiApplicationPrivate::processEnterEvent(static_cast(e));
  22.         break;
  23.     case QWindowSystemInterfacePrivate::Leave:
  24.         QGuiApplicationPrivate::processLeaveEvent(static_cast(e));
  25.         break;
  26.     case QWindowSystemInterfacePrivate::ActivatedWindow:
  27.         QGuiApplicationPrivate::processActivatedEvent(static_cast(e));
  28.         break;
  29.     case QWindowSystemInterfacePrivate::WindowStateChanged:
  30.         QGuiApplicationPrivate::processWindowStateChangedEvent(static_cast(e));
  31.         break;
  32.     case QWindowSystemInterfacePrivate::WindowScreenChanged:
  33.         QGuiApplicationPrivate::processWindowScreenChangedEvent(static_cast(e));
  34.         break;
  35.     case QWindowSystemInterfacePrivate::ApplicationStateChanged: {
  36.         QWindowSystemInterfacePrivate::ApplicationStateChangedEvent * changeEvent = static_cast(e);
  37.         QGuiApplicationPrivate::setApplicationState(changeEvent->newState, changeEvent->forcePropagate); }
  38.         break;
  39.     case QWindowSystemInterfacePrivate::FlushEvents: {
  40.         QWindowSystemInterfacePrivate::FlushEventsEvent *flushEventsEvent = static_cast(e);
  41.         QWindowSystemInterface::deferredFlushWindowSystemEvents(flushEventsEvent->flags); }
  42.         break;
  43.     case QWindowSystemInterfacePrivate::Close:
  44.         QGuiApplicationPrivate::processCloseEvent(
  45.                 static_cast(e));
  46.         break;
  47.     case QWindowSystemInterfacePrivate::ScreenOrientation:
  48.         QGuiApplicationPrivate::reportScreenOrientationChange(
  49.                 static_cast(e));
  50.         break;
  51.     case QWindowSystemInterfacePrivate::ScreenGeometry:
  52.         QGuiApplicationPrivate::reportGeometryChange(
  53.                 static_cast(e));
  54.         break;
  55.     case QWindowSystemInterfacePrivate::ScreenLogicalDotsPerInch:
  56.         QGuiApplicationPrivate::reportLogicalDotsPerInchChange(
  57.                 static_cast(e));
  58.         break;
  59.     case QWindowSystemInterfacePrivate::ScreenRefreshRate:
  60.         QGuiApplicationPrivate::reportRefreshRateChange(
  61.                 static_cast(e));
  62.         break;
  63.     case QWindowSystemInterfacePrivate::ThemeChange:
  64.         QGuiApplicationPrivate::processThemeChanged(
  65.                     static_cast(e));
  66.         break;
  67.     case QWindowSystemInterfacePrivate::Expose:
  68.         QGuiApplicationPrivate::processExposeEvent(static_cast(e));
  69.         break;
  70.     case QWindowSystemInterfacePrivate::Tablet:
  71.         QGuiApplicationPrivate::processTabletEvent(
  72.                     static_cast(e));
  73.         break;
  74.     case QWindowSystemInterfacePrivate::TabletEnterProximity:
  75.         QGuiApplicationPrivate::processTabletEnterProximityEvent(
  76.                     static_cast(e));
  77.         break;
  78.     case QWindowSystemInterfacePrivate::TabletLeaveProximity:
  79.         QGuiApplicationPrivate::processTabletLeaveProximityEvent(
  80.                     static_cast(e));
  81.         break;
  82. #ifndef QT_NO_GESTURES
  83.     case QWindowSystemInterfacePrivate::Gesture:
  84.         QGuiApplicationPrivate::processGestureEvent(
  85.                     static_cast(e));
  86.         break;
  87. #endif
  88.     case QWindowSystemInterfacePrivate::PlatformPanel:
  89.         QGuiApplicationPrivate::processPlatformPanelEvent(
  90.                     static_cast(e));
  91.         break;
  92.     case QWindowSystemInterfacePrivate::FileOpen:
  93.         QGuiApplicationPrivate::processFileOpenEvent(
  94.                     static_cast(e));
  95.         break;
  96. #ifndef QT_NO_CONTEXTMENU
  97.         case QWindowSystemInterfacePrivate::ContextMenu:
  98.         QGuiApplicationPrivate::processContextMenuEvent(
  99.                     static_cast(e));
  100.         break;
  101. #endif
  102.     case QWindowSystemInterfacePrivate::EnterWhatsThisMode:
  103.         QGuiApplication::postEvent(QGuiApplication::instance(), new QEvent(QEvent::EnterWhatsThisMode));
  104.         break;
  105.     default:
  106.         qWarning() << "Unknown user input event type:" << e->type;
  107.         break;
  108.     }
  109. }

2.5 常用的消息过滤事件

通过2.4组装的消息最终到达、此处。经过这些之后:之前的windows消息现在都已映射为QT类型的消息、进入Qt消息处理机制中来、才有了我们的消息过滤等等消息事件键盘鼠标等等；

  1. virtual void mouseDoubleClickEvent(QMouseEvent *event)
  2. virtual void mouseMoveEvent(QMouseEvent *event)
  3. virtual void mousePressEvent(QMouseEvent *event)
  4. virtual void mouseReleaseEvent(QMouseEvent *event)
  5. virtual void moveEvent(QMoveEvent *event)
  6. virtual bool nativeEvent(const QByteArray &eventType, void *message, long *result)
  7. virtual void paintEvent(QPaintEvent *event)
  8. virtual void resizeEvent(QResizeEvent *event)
  9. virtual void showEvent(QShowEvent *event)
  10. virtual void tabletEvent(QTabletEvent *event)
  11. virtual void wheelEvent(QWheelEvent *event)

重新实现上面的消息事件做我们的功能；

总结：

通过windows消息的运行机制与Qt的消息机制进行了对比。其实Qt在windows平台上的消息传递依赖的是windows消息机制。只不过在开始时进行注册消息拦截等一些封装处理、加工成Qt消息在Qt程序中进行传递。

注：本文转载自blog.csdn.net的liuzhezhe111的文章"https://blog.csdn.net/liuzhezhe111/article/details/82154673"。版权归原作者所有，此博客不拥有其著作权，亦不承担相应法律责任。如有侵权，请联系我们删除。
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