[Development] Trigger Qt event loop from external message loop

[Roland Winklmeier]

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Am 14.12.2013 02:16, schrieb Thiago Macieira:
> On sábado, 14 de dezembro de 2013 00:45:20, Roland Winklmeier 
> wrote:
>> Since I cannot run Qt's event loop with QApplication::exec() - I 
>> dont want the plugin to block the parent application - I try to 
>> trigger the event loop externally.
> 
> You have to do that.
> 
> Use another thread then. All of your proposed solutions in your 
> email will run into trouble sooner or later.
> 

Thiago,

thanks for that hint. I changed the plugin to start its own thread. In
this thread I create the QApplication, the dialog and call
QApplication::exec(). Everything fine and clean now besides the
following issue:

In qthread_win.cpp
QThreadPrivate::start ->
void QThreadPrivate::createEventDispatcher(QThreadData *data)
{
    QEventDispatcherWin32 *theEventDispatcher = new QEventDispatcherWin32;
    data->eventDispatcher.storeRelease(theEventDispatcher);
    theEventDispatcher->startingUp();
}

but I expected to have a pointer to QWindowsGuiEventDispatcher which
is a subclass from QEventDispatcherWin32 and located in the QPA plugin.
If I run the standalone application without threading, the event
dispatcher is created in qapplication_qpa.cpp:

void QApplicationPrivate::createEventDispatcher()
{
    QGuiApplicationPrivate::createEventDispatcher();
}
- ->
void QGuiApplicationPrivate::createEventDispatcher()
{
    Q_ASSERT(!eventDispatcher);

    if (platform_integration == 0)
        createPlatformIntegration();

    // The platform integration should not mess with the event dispatcher
    Q_ASSERT(!eventDispatcher);

    // Creates a QWindowsGuiEventDispatcher on windows
    eventDispatcher = platform_integration->createEventDispatcher();
}

So if I run the application in its own thread, QThread creates its
custom event dispatcher, hence no QWindowsGuiEventDispatcher object is
created later in QApplication. But QEventDispatcherWin32 is not
handling window system messages in its sendPostedEvents() method.
Thats why the application does not do anything when I click on buttons.

Does this make sense and could it be fixed, that I get the same event
dispatcher in both cases?
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