Qt中postEvent和sendEvent函數(shù)

部分內(nèi)容參考http://blog.csdn.net/lvmengzou/article/details/65450908

qt事件循環(huán)需要維護(hù)一個(gè)事件隊(duì)列，在Qt的main函數(shù)中最后一般調(diào)用QApplication::exec()成員函數(shù)來(lái)保持程序?qū)κ录?duì)列的處理，exec()的實(shí)質(zhì)是不停調(diào)用processEvent()函數(shù)從隊(duì)列中獲取事件，并處理，然后刪除，postEvent的作用就是發(fā)送一個(gè)事件到此隊(duì)列中，由于刪除隊(duì)列中事件調(diào)用delete運(yùn)算符，所以，postEvent()傳遞的事件一定要是動(dòng)態(tài)分配的。

sendEvent()函數(shù)直接跳過(guò)事件循環(huán)隊(duì)列，直接調(diào)用notify()函數(shù)發(fā)送事件到目標(biāo)對(duì)象，并等待事件處理結(jié)果，所以其傳遞的事件直接在棧上分配即可，(postEvent()函數(shù)只負(fù)責(zé)添加事件到隊(duì)列，不等待事件處理結(jié)果)。

sendEvent調(diào)用關(guān)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(diào)用receiver->event(event);

PostEvent()函數(shù)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(fā)生變化。(有可能是另外一個(gè)線程調(diào)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(gè)事件有可能被壓縮(實(shí)際上是發(fā)現(xiàn)隊(duì)列中有這個(gè)事件還沒(méi)有被處理，且這個(gè)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(gòu)？

}

//將事件添加到postEventList中，注意這里的優(yōu)先級(jí)第一個(gè)最高，最后一個(gè)優(yōu)先級(jí)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(diào)用eventDispatcher處理postEventList

if (data->eventDispatcher)

data->eventDispatcher->wakeUp();

}

如果想查看Qt中QApplication::exec()函數(shù)是如何傳遞事件到目標(biāo)對(duì)象，并根據(jù)notify返回值和事件isAccept()的返回值決定是否傳遞事件到目標(biāo)對(duì)象的父對(duì)象，可以重載目標(biāo)對(duì)象的事件處理函數(shù)，并在事件處理函數(shù)中加入斷點(diǎn)，開(kāi)始調(diào)試，然后在可執(zhí)行程序界面上觸發(fā)事件處理函數(shù)，程序就會(huì)在事件處理函數(shù)的斷點(diǎn)處停止，然后逐級(jí)返回，查看整個(gè)調(diào)用情況，從processEvent()函數(shù)到最終我們重載的事件處理函數(shù)，至少有20層函數(shù)調(diào)用。(調(diào)試之前要安裝Qt源碼組件)

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