Qt中postEvent和sendEvent函数

部分内容参考http://blog.csdn.net/lvmengzou/article/details/65450908

qt事件循环需要维护一个事件队列，在Qt的main函数中最后一般调用QApplication::exec()成员函数来保持程序对事件队列的处理，exec()的实质是不停调用processEvent()函数从队列中获取事件，并处理，然后删除，postEvent的作用就是发送一个事件到此队列中，由于删除队列中事件调用delete运算符，所以，postEvent()传递的事件一定要是动态分配的。

sendEvent()函数直接跳过事件循环队列，直接调用notify()函数发送事件到目标对象，并等待事件处理结果，所以其传递的事件直接在栈上分配即可，(postEvent()函数只负责添加事件到队列，不等待事件处理结果)。

sendEvent调用关系如下：

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)

最终调用receiver->event(event);

PostEvent()函数只是单纯添加事件到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; //得到线程信息

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) { //在这里判断receiver线程信息是否发生变化。(有可能是另外一个线程调用用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();

}

//这里postEventList还是被锁着的。

// 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();//这个事件有可能被压缩(实际上是发现队列中有这个事件还没有被处理，且这个事件是可以被压缩的，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即将被析构？

}

//将事件添加到postEventList中，注意这里的优先级第一个最高，最后一个优先级最低

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();//在这里解除锁

//receiver所在的线程调用eventDispatcher处理postEventList

if (data->eventDispatcher)

data->eventDispatcher->wakeUp();

}

如果想查看Qt中QApplication::exec()函数是如何传递事件到目标对象，并根据notify返回值和事件isAccept()的返回值决定是否传递事件到目标对象的父对象，可以重载目标对象的事件处理函数，并在事件处理函数中加入断点，开始调试，然后在可执行程序界面上触发事件处理函数，程序就会在事件处理函数的断点处停止，然后逐级返回，查看整个调用情况，从processEvent()函数到最终我们重载的事件处理函数，至少有20层函数调用。(调试之前要安装Qt源码组件)