Simple TK Question - refreshing the canvas when not in focus

[Eric Brunel]

On Wed, 30 Apr 2008 10:58:06 +0200, Robert.Spilleboudt   
<robert.spilleboudt.no.sp.am at skynet.be> wrote:

> blaine wrote:
>> Hey everyone!
>>   I'm not very good with Tk, and I am using a very simple canvas to
>> draw some pictures (this relates to that nokia screen emulator I had a
>> post about a few days ago).
>>  Anyway, all is well, except one thing.  When I am not in the program,
>> and the program receives a draw command (from a FIFO pipe), the canvas
>> does not refresh until I click into the program. How do I force it to
>> refresh, or force the window to gain focus?  It seems like pretty
>> common behavior, but a few things that I've tried have not worked.
>>  Class screen():
>>     def __init__(self):
>>         self.root = Tkinter.Tk()
>>         self.root.title('Nokia Canvas')
>>         self.canvas = Tkinter.Canvas(self.root, width =130,
>> height=130)
>>         self.canvas.pack()
>>         self.root.mainloop()
>>  Then somewhere a long the line I do:
>>             self.canvas.create_line(args[0], args[1], args[2],
>> args[3], fill=color)
>>             self.canvas.pack()
>>  I've tried self.root.set_focus(), self.root.force_focus(),
>> self.canvas.update(), etc. but I can't get it.
>> Thanks!
>> Blaine
> When you read the pipe,  do you generate an event? Probably not , and Tk  
> is event-driven and should never update the canvas if there is no event.
> This is how I understand Tk.
>
> I have a Tk program who reads a audio signal (from an RC transmitter) .  
> I generate a event every 100 msec , and "process" refresh the canvas.
> Starting the sequence:
> id = root.after(100,process)  will call "process" after 100 msec
> At the end of "process", repeat:
> id = root.after(100,process)
> Robert

Your method actually works and is in fact even clearer: you explicitely  
give back the control to the main event loop by sending the event. But the  
call to 'update' should also work, since it also gives back the control to  
the main event loop, implicitely however. BTW, the pending events *are*  
treated by a call to update, which can cause some surprises...
-- 
python -c "print ''.join([chr(154 - ord(c)) for c in  
'U(17zX(%,5.zmz5(17l8(%,5.Z*(93-965$l7+-'])"