wxPython before MainLoop

[Chris Mellon]

[david] wrote:

I'd like to refresh the display before I start the main loop.

If your window isn't able to interact with the user, then I'd consider
it a splash screen, no matter if it does look exactly like your main
application interface.

We have this kind of situation in Chandler, where we display and update
the splash screen before we enter MainLoop.
[...]
3. The splash screen refresh is basically: draw new stuff,
self.Layout(), self.Update(), wx.Yield()
http://lxr.osafoundation.org/source/chandler/application/Application.py#1421

Looking at the Chandler code suggests a solution to [david]'s original
problem. It is possible that, on Windows only, he may need to call
Update to finish painting the display.

1432 self.Layout()
1433 if wx.Platform == '__WXMSW__':
1434 self.Update()
1435 wx.GetApp().Yield(True)

wxYield spins the event loop in place. This can have some serious
consequences if you aren't very careful with your usage, like
recursively entering event handlers. I generally consider it an
experts only interface, and avoid it.

I'll confess to being one of those old-school programmers who, back in
the day, wrote his code around big select loops instead of using
threads, but I'm intriged by the "experts only" designation. Can
someone explain further? Thanks!

The biggest problem is recursive events. You can end up entering an
event handler downstack from itself. There's other common problems -
event handlers are generally written to be short and sweet and not to
expect recursion and to complete without interruption. wxYield can
easily end up breaking that. Components that call wxYield are
especially dangerous. For example, some parts of wxWidgets call
wxYield internally. An event handler that aquired a lock was changed
to use one of those components and ended up deadlocking when it was
re-entered by the yield. I've also seen crashes when wxYield processed
a destroy event for a window in the middle of it's own event handler.

Because analyzing your event code to make sure it's reentrant is hard,
and is complicated even more by the fact that wxYield in a component
can cause problems far upstack in a caller, and because there is an
excellent alternative in the form of python generators, I avoid it's
usage from wxPython entirely.

 

[Grant Edwards]

Steve, it wasn't me that raised the comparison
with MFC. If you don't think that's a helpful
comparison, why not reply to that post instead?

I don't mind Björn's suggestion that I don't
know what I'm talking about, because I started
it by telling him he was wrong.

But you don't have that excuse.

(david)

Oh dear, arguing with Steve Holden is a rather inauspicious way
to start out in c.l.p.

 

[[david]]

Looking at the Chandler code suggests a solution

> ... he may need to call Update to finish painting
> the display.

Yes, and thank you to Chandler for pointing that out.

Without the splash screen there was no need to call
Yield or use a generator.

(david)

[david] wrote:

I'd like to refresh the display before I start the main loop.

If your window isn't able to interact with the user, then I'd consider
it a splash screen, no matter if it does look exactly like your main
application interface.

We have this kind of situation in Chandler, where we display and update
the splash screen before we enter MainLoop.
[...]
3. The splash screen refresh is basically: draw new stuff,
self.Layout(), self.Update(), wx.Yield()
http://lxr.osafoundation.org/source/chandler/application/Application.py#1421

Looking at the Chandler code suggests a solution to [david]'s original
problem. It is possible that, on Windows only, he may need to call
Update to finish painting the display.

1432 self.Layout()
1433 if wx.Platform == '__WXMSW__':
1434 self.Update()
1435 wx.GetApp().Yield(True)

wxYield spins the event loop in place. This can have some serious
consequences if you aren't very careful with your usage, like
recursively entering event handlers. I generally consider it an
experts only interface, and avoid it.

I'll confess to being one of those old-school programmers who, back in
the day, wrote his code around big select loops instead of using
threads, but I'm intriged by the "experts only" designation. Can
someone explain further? Thanks!

 

[[david]]

Thanks for that suggestion, and sorry I took so
long to get back to you. That worked.

Because I don't want the splash screen, just
self.Update

regards,

[david]