[PyQt] processEvents on QlistWidget operations does nothing

P. Mathé pmathe at neuf.fr
Mon Jan 28 09:02:29 GMT 2008

Le dimanche 27 janvier 2008, Andreas Pakulat a écrit :
> On 27.01.08 19:37:05, P. Mathé wrote:
> > Le dimanche 27 janvier 2008, Andreas Pakulat a écrit :
> > > On 27.01.08 16:45:36, P. Mathé wrote:
> > > > I am sending you this message, originally sent to the PyQt mailing list, as it seems, according to Phil's answer that the problem lies within Qt.
> > > > As suggested by Phil, I changed the program to make the urllib call from within a different thread, but, if it partially solves the problem, it repaces one line of code by 
> > > > more than fifty, makes the code almost unreadable, and disconnect the QListWidget from the QProgressBar updates. (the new code is at your disposal).
> > > > My point I that I just want that QListWidget works as expected , i.e. that when I say "addItem(...)", I see the item in the UI, now, not later , who knows when.
> > > 
> > > Uhm, the QListWidget does have the item immediately, however the
> > > repainting only happens on the next run of the event loop. Calling
> > > QApplication::processEvents is known to break in certain situations, any
> > > longer-taking operation that shouldn't block the UI simply belongs into
> > > a separate thread or process. Its usage is specifically for those who
> > > know what they're doing.
> > > 
> > > Most of the time you're far better off writing a short QThread subclass
> > > that does the "hard work" and sends either a custom event or simply a
> > > signal using Qt::QueuedConnection.
> > 
> > I did it : the code is awfully ugly just to replace 1 line of code
> Its not about replacing 1 line of code, its about properly designing
> your applications business logic. Moving heavy work into a thread is the
> right thing to do (or separate process). QApplication::processEvents is
> the ugly hack for those who are not able to use threads properly.
> Andreas

Thank you for your answer.
After reading it and Scott Aron's one, I realize that the title of my message is misleading.
It should have been : "QListWidget.addItem does not work as expected".
Introducing processEvents was just a trial to see if it could solve the pb.

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