QT sendEvent()和postEvent()
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QT文档中这样解释:
sendEvent(QObject* receiver,QEvent* event)
使用notify()函数直接给receiver发送事件。
postEvent(QObject* receiver, QEvent* event)
向事件队列中添加receiver和event。
简单说,sendEvent使用的是同步处理事件,postEvent使用的异步处理事件
sendEvent代码分析
- inline bool QCoreApplication::sendEvent(QObject *receiver, QEvent *event)
- { if (event) event->spont = false; return self ? self->notifyInternal(receiver, event) : false; }
直接调用notifyInternal接口,注意中间设置自发消息标志位为false,同时还需要判断self是有有效(QCoreApplication是否启动)- bool QCoreApplication::notifyInternal(QObject *receiver, QEvent *event)
- {
-
-
- bool result = false;
- void *cbdata[] = { receiver, event, &result };
- if (QInternal::activateCallbacks(QInternal::EventNotifyCallback, cbdata)) {
- return result;
- }
-
-
-
-
-
- QObjectPrivate *d = receiver->d_func();
- QThreadData *threadData = d->threadData;
- ++threadData->loopLevel;
-
- bool returnValue = notify(receiver, event);
- --threadData->loopLevel;
- return returnValue;
- }
删除了一些不重要的代码,notifyInternal的主要作用是activateCallbacks,直接看notify- bool QCoreApplication::notify(QObject *receiver, QEvent *event)
- {
- Q_D(QCoreApplication);
-
- if (QCoreApplicationPrivate::is_app_closing)
- return true;
- if (receiver == 0) {
- qWarning("QCoreApplication::notify: Unexpected null receiver");
- return true;
- }
- return receiver->isWidgetType() ? false : d->notify_helper(receiver, event);
- }
这个接口在QT文档上有注释。注意其中当receiver为控件时,不进行处理。- bool QCoreApplicationPrivate::notify_helper(QObject *receiver, QEvent * event)
- {
-
- if (sendThroughApplicationEventFilters(receiver, event))
- return true;
-
- if (sendThroughObjectEventFilters(receiver, event))
- return true;
-
- return receiver->event(event);
- }
在这里可以看到事件是如何处理的:- 先送入Application的事件过滤器,看看是否在事件过滤器中处理
- 再查看receiver是否有此事件的过滤器
- 最后,将事件送入receiver的event接口。
从整个过程来看,可以认为sendEvent直接调用了receiver的event接口。因此,可以认为处理方式为同步处理方式。
PostEvent分析
- 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;
- QThreadData *data = *pdata;
- if (!data) {
-
- delete event;
- return;
- }
-
-
- data->postEventList.mutex.lock();
-
-
- while (data != *pdata) { <span style="font-family: Arial, Helvetica, sans-serif;">
- data->postEventList.mutex.unlock();
-
- data = *pdata;
- if (!data) {
-
- delete event;
- return;
- }
-
- data->postEventList.mutex.lock();
- }
-
-
- if (receiver->d_func()->postedEvents
- && self && self->compressEvent(event, receiver, &data->postEventList)) {
- data->postEventList.mutex.unlock();
- return;
- }
-
- event->posted = true;
- ++receiver->d_func()->postedEvents;
- if (event->type() == QEvent::DeferredDelete && data == QThreadData::current()) {
-
-
- event->d = reinterpret_cast<QEventPrivate *>(quintptr(data->loopLevel));
- }
-
- if (data->postEventList.isEmpty() || data->postEventList.last().priority >= priority) {
-
-
- data->postEventList.append(QPostEvent(receiver, event, priority));
- } else {
-
-
-
- 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();
-
- if (data->eventDispatcher)
- data->eventDispatcher->wakeUp();
- }
从上面可以看出,postEvent实际上是将事件添加到receiver所在线程中的一个队列中,至于这个队列所在的线程什么时候处理这个事件,postEvent是无法控制的
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