[PyKDE] QButton/QGridLayout woes

[David K. Hess]

You mention "from a multithreaded application". Are you being careful  
to keep all Qt activity exclusively in one thread? From http:// 
doc.trolltech.com/3.3/threads.html:

----
In Qt, one thread is always the GUI or event thread. This is the  
thread that creates a QApplication object and calls QApplication::exec 
(). This is also the initial thread that calls main() at program  
start. This thread is the only thread that is allowed to perform GUI  
operations, including generating and receiving events from the window  
system. Qt does not support creating QApplication and running the  
event loop (with QApplication::exec()) in a secondary thread. You  
must create the QApplication object and call QApplication::exec()  
from the main() function in your program.

Threads that wish to display data in a widget cannot modify the  
widget directly, so they must post an event to the widget using  
QApplication::postEvent(). The event will be delivered later on by  
the GUI thread.
----

My guess would be that two threads got into Qt at the same time. It  
may not happen under Linux due to timing differences.

Dave


On Sep 18, 2005, at 10:07 PM, Hoka ME Tichenci wrote:


> I'm having an odd issue with Windows PyQt 3.14.1 Educational, the  
> code is supposed to dynamically add/remove buttons when called from  
> a multithreaded application. On Linux (PyQt 3.13 qt 3.3.4) the code  
> runs fine, but on Windows I get assert problems in a rather odd spot.
>
> The code is here (bgrid is a QGridLayout, bg_projectors is a  
> QButtonGroup):
> print "adding projector rnode: %s" % rnode.getName()
> attrs = rnode.getAttributes()
> print "xpos: %s ypos: %s" % (attrs["xpos"],attrs["ypos"])
> tmp = QPushButton(self.bg_projectors,"yes")
> tmp.setText(rnode.getName())
> print "qpushbutton built"
> self.bgrid.addWidget(tmp,attrs["ypos"],attrs["xpos"])
> print "widget added"
> tmp.show()
> print "Done adding projector!"
>
> However, when run I get this output:
>
> adding projector rnode: Projector: BigOne
> xpos: 1 ypos: 1
> qpushbutton built
> projector is off
> widget added
> Done adding projector!
> ASSERT: "src_dc && dst_dc" in kernel\qpaintdevice_win.cpp (388)
>
> What's odd is that the ASSERT failure is at the end, after the  
> method should be done and printed its last statement. Furthermore,  
> if I make a QWarningBox or other similar piece of code pauses the  
> system after tmp.show() is called, the QButton can be seen in the  
> background, after the box is closed the button disappears, but  
> oddly enough no ASSERT is thrown. This may not be the right way to  
> do something like this, and if it isn't correct me, but I'm at a  
> lost and Google didn't return anything worthwhile.
>
> Thanks for your time,
> -Hoka
>
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