分析Qt源码一则想自己在开发学习中有积累，同时自己也一直有一种理念，使用她那么就更深入的认识她。 如果有分析不正确的，还烦请各位看官指正。
- 事件分发器创建
在QCoreApplication构造函数中
if (!QCoreApplicationPrivate::eventDispatcher)
d->createEventDispatcher();
接着
void QGuiApplicationPrivate::createEventDispatcher()
{
Q_ASSERT(!eventDispatcher);
if (platform_integration == 0)
createPlatformIntegration();
// The platform integration should not mess with the event dispatcher
Q_ASSERT(!eventDispatcher);
eventDispatcher = platform_integration->createEventDispatcher();
}
如果是windows平台
QAbstractEventDispatcher * QWindowsIntegration::createEventDispatcher() const
{
return new QWindowsGuiEventDispatcher;
}
而这里的QWindowsGuiEventDispatcher是QEventDispatcherWin32的子类
QWindowsGuiEventDispatcher::QWindowsGuiEventDispatcher(QObject *parent) :
QEventDispatcherWin32(parent), m_flags(0)
{
setObjectName(QStringLiteral("QWindowsGuiEventDispatcher"));
createInternalHwnd(); // QTBUG-40881: Do not delay registering timers, etc. for QtMfc.
}
- 这里每一个事件分发器创建后都会创建一个内部窗口，这个窗口虽然不显示，但是却是非常重要的，一些自定义消息都是在这个窗口的过程回调中处理
void QEventDispatcherWin32::createInternalHwnd()
{
Q_D(QEventDispatcherWin32);
if (d->internalHwnd)
return;
d->internalHwnd = qt_create_internal_window(this);
installMessageHook();
// start all normal timers
for (int i = 0; i < d->timerVec.count(); ++i)
d->registerTimer(d->timerVec.at(i));
}
内部窗口的过程函数：
LRESULT QT_WIN_CALLBACK qt_internal_proc(HWND hwnd, UINT message, WPARAM wp, LPARAM lp)
{
if (message == WM_NCCREATE)
return true;
MSG msg;
msg.hwnd = hwnd;
msg.message = message;
msg.wParam = wp;
msg.lParam = lp;
QAbstractEventDispatcher* dispatcher = QAbstractEventDispatcher::instance();
long result;
if (!dispatcher) {
if (message == WM_TIMER)
KillTimer(hwnd, wp);
return 0;
} else if (dispatcher->filterNativeEvent(QByteArrayLiteral("windows_dispatcher_MSG"), &msg, &result)) {
return result;
}
#ifdef GWLP_USERDATA
QEventDispatcherWin32 *q = (QEventDispatcherWin32 *) GetWindowLongPtr(hwnd, GWLP_USERDATA);
#else
QEventDispatcherWin32 *q = (QEventDispatcherWin32 *) GetWindowLong(hwnd, GWL_USERDATA);
#endif
QEventDispatcherWin32Private *d = 0;
if (q != 0)
d = q->d_func();
if (message == WM_QT_SOCKETNOTIFIER) {
// socket notifier message
int type = -1;
switch (WSAGETSELECTEVENT(lp)) {
case FD_READ:
case FD_ACCEPT:
type = 0;
break;
case FD_WRITE:
case FD_CONNECT:
type = 1;
break;
case FD_OOB:
type = 2;
break;
case FD_CLOSE:
type = 3;
break;
}
if (type >= 0) {
Q_ASSERT(d != 0);
QSNDict *sn_vec[4] = { &d->sn_read, &d->sn_write, &d->sn_except, &d->sn_read };
QSNDict *dict = sn_vec[type];
QSockNot *sn = dict ? dict->value(wp) : 0;
if (sn) {
d->doWsaAsyncSelect(sn->fd, 0);
d->active_fd[sn->fd].selected = false;
d->postActivateSocketNotifiers();
if (type < 3) {
QEvent event(QEvent::SockAct);
QCoreApplication::sendEvent(sn->obj, &event);
} else {
QEvent event(QEvent::SockClose);
QCoreApplication::sendEvent(sn->obj, &event);
}
}
}
return 0;
} else if (message == WM_QT_ACTIVATENOTIFIERS) {
Q_ASSERT(d != 0);
// register all socket notifiers
for (QSFDict::iterator it = d->active_fd.begin(), end = d->active_fd.end();
it != end; ++it) {
QSockFd &sd = it.value();
if (!sd.selected) {
d->doWsaAsyncSelect(it.key(), sd.event);
sd.selected = true;
}
}
d->activateNotifiersPosted = false;
return 0;
} else if (message == WM_QT_SENDPOSTEDEVENTS
// we also use a Windows timer to send posted events when the message queue is full
|| (message == WM_TIMER
&& d->sendPostedEventsWindowsTimerId != 0
&& wp == (uint)d->sendPostedEventsWindowsTimerId)) {
const int localSerialNumber = d->serialNumber.load();
if (localSerialNumber != d->lastSerialNumber) {
d->lastSerialNumber = localSerialNumber;
q->sendPostedEvents();
}
return 0;
} else if (message == WM_TIMER) {
Q_ASSERT(d != 0);
d->sendTimerEvent(wp);
return 0;
}
return DefWindowProc(hwnd, message, wp, lp);
}
我们需要区分的是这里的内部窗口和应用创建的Native窗口的区别(Native窗口后面源码分析再说)
这里处理内部创建
- socket消息，也是Qt内部自定义的消息WM_QT_SOCKETNOTIFIER
- postEvent到一些对象的消息，也是自定义消息WM_QT_SENDPOSTEDEVENTS
- 通过QObject注册的定时器消息WM_TIMER
最终转成事件直接发送到相应的对象处理。
- 现在有了事件分发器这个消息处理发动机，发动机是如何启动的呢？
在QApplication的exec()或者QEventLoop的exec()启动了事件循环
继续跟踪代码
void QEventLoop::processEvents(ProcessEventsFlags flags, int maxTime)
{
Q_D(QEventLoop);
if (!d->threadData->eventDispatcher.load())
return;
QElapsedTimer start;
start.start();
while (processEvents(flags & ~WaitForMoreEvents)) {
if (start.elapsed() > maxTime)
break;
}
}
bool QEventLoop::processEvents(ProcessEventsFlags flags)
{
Q_D(QEventLoop);
if (!d->threadData->eventDispatcher.load())
return false;
return d->threadData->eventDispatcher.load()->processEvents(flags);
}
最后还是事件分发器一直处理事件：
bool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags)
{
Q_D(QEventDispatcherWin32);
if (!d->internalHwnd) {
createInternalHwnd();
wakeUp(); // trigger a call to sendPostedEvents()
}
d->interrupt = false;
emit awake();
bool canWait;
bool retVal = false;
bool seenWM_QT_SENDPOSTEDEVENTS = false;
bool needWM_QT_SENDPOSTEDEVENTS = false;
do {
DWORD waitRet = 0;
HANDLE pHandles[MAXIMUM_WAIT_OBJECTS - 1];
QVarLengthArray<MSG> processedTimers;
while (!d->interrupt) {
DWORD nCount = d->winEventNotifierList.count();
Q_ASSERT(nCount < MAXIMUM_WAIT_OBJECTS - 1);
MSG msg;
bool haveMessage;
if (!(flags & QEventLoop::ExcludeUserInputEvents) && !d->queuedUserInputEvents.isEmpty()) {
// process queued user input events
haveMessage = true;
msg = d->queuedUserInputEvents.takeFirst();
} else if(!(flags & QEventLoop::ExcludeSocketNotifiers) && !d->queuedSocketEvents.isEmpty()) {
// process queued socket events
haveMessage = true;
msg = d->queuedSocketEvents.takeFirst();
} else {
haveMessage = PeekMessage(&msg, 0, 0, 0, PM_REMOVE);
if (haveMessage) {
if ((flags & QEventLoop::ExcludeUserInputEvents)
&& ((msg.message >= WM_KEYFIRST
&& msg.message <= WM_KEYLAST)
|| (msg.message >= WM_MOUSEFIRST
&& msg.message <= WM_MOUSELAST)
|| msg.message == WM_MOUSEWHEEL
|| msg.message == WM_MOUSEHWHEEL
|| msg.message == WM_TOUCH
#ifndef QT_NO_GESTURES
|| msg.message == WM_GESTURE
|| msg.message == WM_GESTURENOTIFY
#endif
|| msg.message == WM_CLOSE)) {
// queue user input events for later processing
d->queuedUserInputEvents.append(msg);
continue;
}
if ((flags & QEventLoop::ExcludeSocketNotifiers)
&& (msg.message == WM_QT_SOCKETNOTIFIER && msg.hwnd == d->internalHwnd)) {
// queue socket events for later processing
d->queuedSocketEvents.append(msg);
continue;
}
}
}
if (!haveMessage) {
// no message - check for signalled objects
for (int i=0; i<(int)nCount; i++)
pHandles[i] = d->winEventNotifierList.at(i)->handle();
waitRet = MsgWaitForMultipleObjectsEx(nCount, pHandles, 0, QS_ALLINPUT, MWMO_ALERTABLE);
if ((haveMessage = (waitRet == WAIT_OBJECT_0 + nCount))) {
// a new message has arrived, process it
continue;
}
}
if (haveMessage) {
// WinCE doesn't support hooks at all, so we have to call this by hand :(
if (!d->getMessageHook)
(void) qt_GetMessageHook(0, PM_REMOVE, (LPARAM) &msg);
if (d->internalHwnd == msg.hwnd && msg.message == WM_QT_SENDPOSTEDEVENTS) {
if (seenWM_QT_SENDPOSTEDEVENTS) {
// when calling processEvents() "manually", we only want to send posted
// events once
needWM_QT_SENDPOSTEDEVENTS = true;
continue;
}
seenWM_QT_SENDPOSTEDEVENTS = true;
} else if (msg.message == WM_TIMER) {
// avoid live-lock by keeping track of the timers we've already sent
bool found = false;
for (int i = 0; !found && i < processedTimers.count(); ++i) {
const MSG processed = processedTimers.constData()[i];
found = (processed.wParam == msg.wParam && processed.hwnd == msg.hwnd && processed.lParam == msg.lParam);
}
if (found)
continue;
processedTimers.append(msg);
} else if (msg.message == WM_QUIT) {
if (QCoreApplication::instance())
QCoreApplication::instance()->quit();
return false;
}
if (!filterNativeEvent(QByteArrayLiteral("windows_generic_MSG"), &msg, 0)) {
TranslateMessage(&msg);
DispatchMessage(&msg);
}
} else if (waitRet - WAIT_OBJECT_0 < nCount) {
d->activateEventNotifier(d->winEventNotifierList.at(waitRet - WAIT_OBJECT_0));
} else {
// nothing todo so break
break;
}
retVal = true;
}
// still nothing - wait for message or signalled objects
canWait = (!retVal
&& !d->interrupt
&& (flags & QEventLoop::WaitForMoreEvents));
if (canWait) {
DWORD nCount = d->winEventNotifierList.count();
Q_ASSERT(nCount < MAXIMUM_WAIT_OBJECTS - 1);
for (int i=0; i<(int)nCount; i++)
pHandles[i] = d->winEventNotifierList.at(i)->handle();
emit aboutToBlock();
waitRet = MsgWaitForMultipleObjectsEx(nCount, pHandles, INFINITE, QS_ALLINPUT, MWMO_ALERTABLE | MWMO_INPUTAVAILABLE);
emit awake();
if (waitRet - WAIT_OBJECT_0 < nCount) {
d->activateEventNotifier(d->winEventNotifierList.at(waitRet - WAIT_OBJECT_0));
retVal = true;
}
}
} while (canWait);
if (!seenWM_QT_SENDPOSTEDEVENTS && (flags & QEventLoop::EventLoopExec) == 0) {
// when called "manually", always send posted events
sendPostedEvents();
}
if (needWM_QT_SENDPOSTEDEVENTS)
PostMessage(d->internalHwnd, WM_QT_SENDPOSTEDEVENTS, 0, 0);
return retVal;
}
注意到关键的Windows消息循环的API：
PeekMessage(&msg, 0, 0, 0, PM_REMOVE);
从消息队列里面取消息
TranslateMessage(&msg);
转化消息
DispatchMessage(&msg);
分发消息到窗口过程函数
那么源源不断的窗口消息被分发到过程函数中进行处理。
上面我们说到了一些自定义的消息被内部窗口过程函数接收，后面讲我们会讲到窗口的创建和窗口过程函数，窗口消息、然后转成事件被发送到相应的widget。