詳解 QT 源碼之 Qt 事件機制原理
作者：佚名
本文介紹的是 QT 源碼之 Qt 事件機制原理，解決在用Qt寫Gui程序的時候，出現(xiàn)的問題，先來看本文.
QT 源碼之 Qt 事件機制原理是本文要介紹的內(nèi)容，在用Qt寫Gui程序的時候，在main函數(shù)里面最后依據(jù)都是app.exec();很多書上對這句的解釋是，使 Qt 程序進入消息循環(huán)。下面我們就到exec()函數(shù)內(nèi)部，來看一下他的實現(xiàn)原理。
Let's go!
首先來到QTDIR\src\corelib\kernel\qcoreapplication.cpp
- int QCoreApplication::exec()
- {
- if (!QCoreApplicationPrivate::checkInstance("exec"))
- return -1;
- //獲取線程數(shù)據(jù)
- QThreadData *threadData = self->d_func()->threadData;
- //判斷是否在主線程創(chuàng)建
- if (threadData != QThreadData::current()) {
- qWarning("%s::exec: Must be called from the main thread", self->metaObject()->className());
- return -1;
- }
- //判斷eventLoop是否已經(jīng)創(chuàng)建
- if (!threadData->eventLoops.isEmpty()) {
- qWarning("QCoreApplication::exec: The event loop is already running");
- return -1;
- }
- threadData->quitNow = false;
- QEventLoop eventLoop;
- self->d_func()->in_exec = true;
- //創(chuàng)建eventLoop
- int returnCode = eventLoop.exec();
- threadData->quitNow = false;
- if (self) {
- self->d_func()->in_exec = false;
- //退出程序
- emit self->aboutToQuit();
- sendPostedEvents(0, QEvent::DeferredDelete);
- }
- return returnCode;
- }
- 再來到qeventloop.cpp中。
- int QEventLoop::exec(ProcessEventsFlags flags)
- {
- Q_D(QEventLoop);
- if (d->threadData->quitNow)
- return -1;
- //已經(jīng)調(diào)用過exec了。
- if (d->inExec) {
- qWarning("QEventLoop::exec: instance %p has already called exec()", this);
- return -1;
- }
- d->inExec = true;
- d->exit = false;
- ++d->threadData->loopLevel;
- //將事件類對象壓入線程結(jié)構(gòu)體中
- d->threadData->eventLoops.push(this);
- // remove posted quit events when entering a new event loop
- // 這句不用翻譯了把！
- if (qApp->thread() == thread())
- QCoreApplication::removePostedEvents(qApp, QEvent::Quit);
- #if defined(QT_NO_EXCEPTIONS)
- while (!d->exit)
- //這里才是關鍵,我們還要繼續(xù)跟蹤進去。
- processEvents(flags | WaitForMoreEvents);
- #else
- try {
- while (!d->exit)
- processEvents(flags | WaitForMoreEvents);
- } catch (...) {
- //如果使用了EXCEPTION，則繼續(xù)對下一條時間進行處理。
- qWarning("Qt has caught an exception thrown from an event handler. Throwing\n"
- "exceptions from an event handler is not supported in Qt. You must\n"
- "reimplement QApplication::notify() and catch all exceptions there.\n");
- throw;
- }
- #endif
- //退出eventloop前，將時間對象從線程結(jié)構(gòu)中取出。
- QEventLoop *eventLoop = d->threadData->eventLoops.pop();
- Q_ASSERT_X(eventLoop == this, "QEventLoop::exec()", "internal error");
- Q_UNUSED(eventLoop); // --release warning
- d->inExec = false;
- --d->threadData->loopLevel;
- //退出事件循環(huán)。
- return d->returnCode;
- }
- 來到了processEvents函數(shù)：
- bool QEventLoop::processEvents(ProcessEventsFlags flags)
- {
- Q_D(QEventLoop);
- //判斷事件分派器是否為空。
- if (!d->threadData->eventDispatcher)
- return false;
- if (flags & DeferredDeletion)
- QCoreApplication::sendPostedEvents(0, QEvent::DeferredDelete);
- //調(diào)用不同平臺下的事件分派器來處理事件。
- return d->threadData->eventDispatcher->processEvents(flags);
- }
- processEvents是在QAbstractEventDispatcher類中定義的純虛方法。在QEventDispatcherWin32類有processEvents的實現(xiàn)。
- bool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags)
- {
- Q_D(QEventDispatcherWin32);
- //內(nèi)部數(shù)據(jù)創(chuàng)建。registerClass注冊窗口類，createwindow創(chuàng)建窗體。
- //注冊socket notifiers，啟動所有的normal timers
- if (!d->internalHwnd)
- createInternalHwnd();
- d->interrupt = false;
- emit awake();
- bool canWait;
- bool retVal = false;
- do {
- QCoreApplicationPrivate::sendPostedEvents(0, 0, d->threadData);
- DWORD waitRet = 0;
- HANDLE pHandles[MAXIMUM_WAIT_OBJECTS - 1];
- QVarLengthArray<MSG> processedTimers;
- while (!d->interrupt) {
- DWORD nCount = d->winEventNotifierList.count();
- Q_ASSERT(nCount < MAXIMUM_WAIT_OBJECTS - 1);
- MSG msg;
- bool haveMessage;
- if (!(flags & QEventLoop::ExcludeUserInputEvents) && !d->queuedUserInputEvents.isEmpty()) {
- // process queued user input events處理用戶輸入事件，放入隊列中。
- haveMessage = true;
- msg = d->queuedUserInputEvents.takeFirst();
- } else if(!(flags & QEventLoop::ExcludeSocketNotifiers) && !d->queuedSocketEvents.isEmpty()) {
- // process queued socket events 處理socket事件，放入隊列中。
- haveMessage = true;
- msg = d->queuedSocketEvents.takeFirst();
- } else {
- //從消息隊列中取消息，同PeekMessage
- haveMessage = winPeekMessage(&msg, 0, 0, 0, PM_REMOVE);
- if (haveMessage && (flags & QEventLoop::ExcludeUserInputEvents)
- && ((msg.message >= WM_KEYFIRST
- && msg.message <= WM_KEYLAST)
- || (msg.message >= WM_MOUSEFIRST
- && msg.message <= WM_MOUSELAST)
- || msg.message == WM_MOUSEWHEEL)) {
- // queue user input events for later processing
- haveMessage = false;
- d->queuedUserInputEvents.append(msg);
- }
- if (haveMessage && (flags & QEventLoop::ExcludeSocketNotifiers)
- && (msg.message == WM_USER && msg.hwnd == d->internalHwnd)) {
- // queue socket events for later processing
- haveMessage = false;
- d->queuedSocketEvents.append(msg);
- }
- }
- if (!haveMessage) {
- // no message - check for signalled objects
- for (int i=0; i<(int)nCount; i++)
- pHandles[i] = d->winEventNotifierList.at(i)->handle();
- //注冊signal--slot。
- waitRet = MsgWaitForMultipleObjectsEx(nCount, pHandles, 0, QS_ALLINPUT, MWMO_ALERTABLE);
- if ((haveMessage = (waitRet == WAIT_OBJECT_0 + nCount))) {
- // a new message has arrived, process it
- continue;
- }
- }
- //事件隊列中有事件需要處理。
- if (haveMessage) {
- //處理timer事件
- if (msg.message == WM_TIMER) {
- // avoid live-lock by keeping track of the timers we've already sent
- bool found = false;
- for (int i = 0; !found && i < processedTimers.count(); ++i) {
- const MSG processed = processedTimers.constData()[i];
- found = (processed.wParam == msg.wParam && processed.hwnd == msg.hwnd && processed.lParam == msg.lParam);
- }
- if (found)
- continue;
- processedTimers.append(msg);
- } else if (msg.message == WM_QUIT) {
- if (QCoreApplication::instance())
- QCoreApplication::instance()->quit();
- return false;
- }
- //消息分發(fā)處理。
- if (!filterEvent(&msg)) {
- TranslateMessage(&msg);
- QT_WA({
- DispatchMessage(&msg);
- } , {
- DispatchMessageA(&msg);
- });
- }
- } else if (waitRet >= WAIT_OBJECT_0 && waitRet < WAIT_OBJECT_0 + nCount) {
- //處理signal--slot
- d->activateEventNotifier(d->winEventNotifierList.at(waitRet - WAIT_OBJECT_0));
- } else {
- // nothing todo so break
- break;
- }
- retVal = true;
- }
- // still nothing - wait for message or signalled objects
- QThreadData *ddata = d->threadData;
- canWait = (!retVal
- && data->canWait
- && !d->interrupt
- && (flags & QEventLoop::WaitForMoreEvents));
- if (canWait) {
- DWORD nCount = d->winEventNotifierList.count();
- Q_ASSERT(nCount < MAXIMUM_WAIT_OBJECTS - 1);
- for (int i=0; i<(int)nCount; i++)
- pHandles[i] = d->winEventNotifierList.at(i)->handle();
- emit aboutToBlock();
- waitRet = MsgWaitForMultipleObjectsEx(nCount, pHandles, INFINITE, QS_ALLINPUT, MWMO_ALERTABLE);
- emit awake();
- if (waitRet >= WAIT_OBJECT_0 && waitRet < WAIT_OBJECT_0 + nCount) {
- d->activateEventNotifier(d->winEventNotifierList.at(waitRet - WAIT_OBJECT_0));
- retVal = true;
- }
- }
- } while (canWait);
- return retVal;
- }
小結(jié)：關于詳解 QT 源碼之 Qt 事件機制原理的內(nèi)容介紹完了，基本屬于代碼實現(xiàn)的內(nèi)容，最后希望本文對你有幫助！
責任編輯：zhaolei
來源：
互聯(lián)網(wǎng)
