Qt中事件分发源代码剖析
Qt中事件传递顺序：
在一个应该程序中，会进入一个事件循环，接受系统产生的事件，并且进行分发，这些都是在exec中进行的。
下面举例说明：
1)首先看看下面一段示例代码：
- int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MouseEvent w;
w.show();
return a.exec();
}
2)a.exec进入事件循环，调用的是QApplication::exec()；
- int QApplication::exec()
{
return <span style="color:#ff6666;">QGuiApplication::exec();</span>
}
3)QApplication::exec()调用的是QGuiApplication::exec()；
- int QGuiApplication::exec()
{
#ifndef QT_NO_ACCESSIBILITY
QAccessible::setRootObject(qApp);
#endif
return QCoreApplication::exec();
}
4)QGuiApplication::exec()调用的是QCoreApplication::exec()；
- int QCoreApplication::exec()
{
if (!QCoreApplicationPrivate::checkInstance("exec"))
return -1;
QThreadData *threadData = self->d_func()->threadData;
if (threadData != QThreadData::current()) {
qWarning("%s::exec: Must be called from the main thread", self->metaObject()->className());
return -1;
}
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;
self->d_func()->aboutToQuitEmitted = false;
int returnCode = eventLoop.exec();
threadData->quitNow = false;
if (self) {
self->d_func()->in_exec = false;
if (!self->d_func()->aboutToQuitEmitted)
emit self->aboutToQuit(QPrivateSignal());
self->d_func()->aboutToQuitEmitted = true;
sendPostedEvents(0, QEvent::DeferredDelete);
}
return returnCode;
}
5)QCoreApplication::exec()调用eventLoop.exec()进行事件循环；
- int QEventLoop::exec(ProcessEventsFlags flags)
{
Q_D(QEventLoop);
//we need to protect from race condition with QThread::exit
QMutexLocker locker(&static_cast<QThreadPrivate *>(QObjectPrivate::get(d->threadData->thread))->mutex);
if (d->threadData->quitNow)
return -1;
if (d->inExec) {
qWarning("QEventLoop::exec: instance %p has already called exec()", this);
return -1;
}
struct LoopReference {
QEventLoopPrivate *d;
QMutexLocker &locker;
bool exceptionCaught;
LoopReference(QEventLoopPrivate *d, QMutexLocker &locker) : d(d), locker(locker), exceptionCaught(true)
{
d->inExec = true;
d->exit = false;
++d->threadData->loopLevel;
d->threadData->eventLoops.push(d->q_func());
locker.unlock();
}
~LoopReference()
{
if (exceptionCaught) {
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");
}
locker.relock();
QEventLoop *eventLoop = d->threadData->eventLoops.pop();
Q_ASSERT_X(eventLoop == d->q_func(), "QEventLoop::exec()", "internal error");
Q_UNUSED(eventLoop); // --release warning
d->inExec = false;
--d->threadData->loopLevel;
}
};
LoopReference ref(d, locker);
// remove posted quit events when entering a new event loop
QCoreApplication *app = QCoreApplication::instance();
if (app && app->thread() == thread())
QCoreApplication::removePostedEvents(app, QEvent::Quit);
while (!d->exit)
processEvents(flags | WaitForMoreEvents | EventLoopExec);
ref.exceptionCaught = false;
return d->returnCode;
}
6)eventLoop.exec()调用QCoreApplication的processEvents进行事件分发；
7)调用notify进行分发
QCoreApplication::sendEvent、QCoreApplication::postEvent和QCoreApplication::sendPostedEvents都调用notify进行事件分发；
- bool QCoreApplication::notify(QObject *receiver, QEvent *event)
{
Q_D(QCoreApplication);
// no events are delivered after ~QCoreApplication() has started
if (QCoreApplicationPrivate::is_app_closing)
return true;
if (receiver == 0) { // serious error
qWarning("QCoreApplication::notify: Unexpected null receiver");
return true;
}
#ifndef QT_NO_DEBUG
d->checkReceiverThread(receiver);
#endif
return receiver->isWidgetType() ? false :<span style="color:#ff6666;"> d->notify_helper</span>(receiver, event);
}
8)notify调用notify_helper进行事件分发；
- bool QCoreApplicationPrivate::notify_helper(QObject *receiver, QEvent * event)
{
// send to all application event filters
if (sendThroughApplicationEventFilters(receiver, event))
return true;
// send to all receiver event filters
if (sendThroughObjectEventFilters(receiver, event))
return true;
// deliver the event
return receiver->event(event);
}
9)从上面第8步的代码可以看出事件传递
传递的顺序是：首先传递给全局的事件过滤器，再传递给目标对象的事件过滤器，最终传递给目标对象。
http://blog.csdn.net/chenlong12580/article/details/25009095
