Qt中postEvent和sendEvent函數

部分內容參考http://blog.csdn.net/lvmengzou/article/details/65450908

qt事件循環需要維護一個事件隊列，在Qt的main函數中最后一般調用QApplication::exec()成員函數來保持程序對事件隊列的處理，exec()的實質是不停調用processEvent()函數從隊列中獲取事件，并處理，然后刪除，postEvent的作用就是發送一個事件到此隊列中，由于刪除隊列中事件調用delete運算符，所以，postEvent()傳遞的事件一定要是動態分配的。

sendEvent()函數直接跳過事件循環隊列，直接調用notify()函數發送事件到目標對象，并等待事件處理結果，所以其傳遞的事件直接在棧上分配即可，(postEvent()函數只負責添加事件到隊列，不等待事件處理結果)。

sendEvent調用關系如下：

inline bool QCoreApplication::sendEvent(QObject *receiver, QEvent *event)

{ if (event) event->spont = false; return self ? self->notifyInternal(receiver, event) : false; }

QCoreApplication::notifyInternal(QObject * receiver, QEvent * event)

QCoreApplication::notify(QObject * receiver, QEvent *event)

QCoreApplicationPrivate::notify_helper(QObject * receiver, QEvent * event)

最終調用receiver->event(event);

PostEvent()函數只是單純添加事件到postEventList

void QCoreApplication::postEvent(QObject *receiver, QEvent *event)

{

postEvent(receiver, event, Qt::NormalEventPriority);

}

void QCoreApplication::postEvent(QObject *receiver, QEvent *event, int priority)

{

...

QThreadData * volatile * pdata = &receiver->d_func()->threadData; //得到線程信息

QThreadData *data = *pdata;

if (!data) {

// posting during destruction? just delete the event to prevent a leak

delete event;

return;

}

// lock the post event mutex

data->postEventList.mutex.lock();

// if object has moved to another thread, follow it

while (data != *pdata) { //在這里判斷receiver線程信息是否發生變化。(有可能是另外一個線程調用用receiver->moveToThread)

data->postEventList.mutex.unlock();

data = *pdata;

if (!data) {

// posting during destruction? just delete the event to prevent a leak

delete event;

return;

}

data->postEventList.mutex.lock();

}

//這里postEventList還是被鎖著的。

// if this is one of the compressible events, do compression

if (receiver->d_func()->postedEvents

&& self && self->compressEvent(event, receiver, &data->postEventList)) {

data->postEventList.mutex.unlock();//這個事件有可能被壓縮(實際上是發現隊列中有這個事件還沒有被處理，且這個事件是可以被壓縮的，例如paintevent)

return;

}

event->posted = true;

++receiver->d_func()->postedEvents;

if (event->type() == QEvent::DeferredDelete && data == QThreadData::current()) {

// remember the current running eventloop for DeferredDelete

// events posted in the receiver's thread

event->d = reinterpret_cast(quintptr(data->loopLevel)); //receiver即將被析構？

}

//將事件添加到postEventList中，注意這里的優先級第一個最高，最后一個優先級最低

if (data->postEventList.isEmpty() || data->postEventList.last().priority >= priority) {

// optimization: we can simply append if the last event in

// the queue has higher or equal priority

data->postEventList.append(QPostEvent(receiver, event, priority));

} else {

// insert event in descending priority order, using upper

// bound for a given priority (to ensure proper ordering

// of events with the same priority)

QPostEventList::iterator begin = data->postEventList.begin()

+ data->postEventList.insertionOffset,

end = data->postEventList.end();

QPostEventList::iterator at = qUpperBound(begin, end, priority);

data->postEventList.insert(at, QPostEvent(receiver, event, priority));

}

data->canWait = false;

data->postEventList.mutex.unlock();//在這里解除鎖

//receiver所在的線程調用eventDispatcher處理postEventList

if (data->eventDispatcher)

data->eventDispatcher->wakeUp();

}

如果想查看Qt中QApplication::exec()函數是如何傳遞事件到目標對象，并根據notify返回值和事件isAccept()的返回值決定是否傳遞事件到目標對象的父對象，可以重載目標對象的事件處理函數，并在事件處理函數中加入斷點，開始調試，然后在可執行程序界面上觸發事件處理函數，程序就會在事件處理函數的斷點處停止，然后逐級返回，查看整個調用情況，從processEvent()函數到最終我們重載的事件處理函數，至少有20層函數調用。(調試之前要安裝Qt源碼組件)

總結

以上是生活随笔為你收集整理的qt中sendevent_Qt中postEvent和sendEvent函数的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。