[Tkinter-discuss] Persuading after_idle callback to only get called when the window is mapped

[Michael Lange]

Hi Geoff,

On Wed, 13 Jan 2010 22:41:55 +0100
Geoff Bache <geoff.bache at gmail.com> wrote:

(...)
> 
> Hi Michael,
> 
> Thanks for your detailed reply. I feel also that there should be a
> simpler solution and I can't say I *want* to use threads exactly. What
> I think you're missing above is that a GUI testing tool is supposed to
> deal with an arbitrary application under test so I don't have any
> control over the widgets and how they're packed. That also makes it
> difficult to call root.update() because I don't know when the
> application would be ready for me to do so.
> 

Hmm, from your previous posts I thought you would just do the call to
root.after_idle(self.replayEvents) right before root.mainloop() ?
If so, why not do

    root.deiconify()
    root.update()
    root.after_idle(self.replayEvents)
    root.mainloop()

I don't think there is any risk in using update() like this. I am
afraid I did not understand you properly though, and what you are trying
is more complex than I thought. I actually don't have any experience
with gui testing tools :)
Another idea, which looks a little hackish, but maybe does the trick as
well, is to add a test if the window is visible to the replayEvents()
method and if not call it again after 100 ms or so, like:

    def replayEvents(self):
        if root.winfo_ismapped():
            # do things....
        else:
            root.after(100, self.replayEvents)

Really not nice, but simple (and maybe effective?).

Regards

Michael

> In any case, the documentation for update() is as follows:
> 
> "This method forces the updating of the display. It should be used
> only if you know what you're doing, since it can lead to unpredictable
> behavior or looping. It should never be called from an event callback
> or a function that is called from an event callback."
> 
> makes it sound just about as risky as what I'm doing at the moment...
> especially as I can't really claim I know what I'm doing having looked
> at tkinter for the first time less than a week ago :)
> 
> Regards,
> Geoff
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