[PyQt] Threads with PyQt. Qt's or Python's?

Frédéric frederic.mantegazza at gbiloba.org
Tue Feb 3 09:56:53 GMT 2009

Le 19/1/2009, "Giovanni Bajo" <rasky at develer.com> a écrit:

>This would work on Qt4 as well, but of course it's not ideal as you need 
>a timer to poll the queue. It's much easier to use QThreads and simply 
>post the events (or use the asynchronous signals).
>Plus, you can now do non-trivial things from the secondary threads (eg: 
>painting with QPainter over a QImage) so it's worth sitting down and 
>analyzing all these possibilities before desiging the code with Qt4.

I started to use QThreads, and I have some minor problems.

When my app was build on PyGTK, I was using standard python threads, and
a serializer to push PyGTK calls from the threads. The serializer queue
was periodically read and executed from the main thread.

I replaced the python threads by QThread, and removed all serializer
calls. This works pretty well (and faster), except for one thing: I
can't refresh my progressbar from the thread. Doing this output the
following message:

    QPixmap: It is not safe to use pixmaps outside the GUI thread
    QPainter: It is not safe to use drawPixmap() outside the GUI thread

The documentation says that a QPainter can only paint on QImage, QPrinter
and QPicture, but not on QWidget and QPixmap (it seems that painting on
QGraphicsItem works fine, as I don't have warnings; can you confirm?).

So, how can I refresh my progressbar from my thread? Is there a Qt
mecanism I could use? I'm not that familiar with Qt custom
events/signals or so...



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