Simple TK Question - refreshing the canvas when not in focus

[Eric Brunel]

On Wed, 30 Apr 2008 20:19:32 +0200, blaine <frikker at gmail.com> wrote:

> On Apr 30, 10:41 am, Peter Otten <__pete... at web.de> wrote:
>> blaine wrote:
>> > Still doesn't work.  I'm looking into using wx instead...
>>
>> > This is the full code - does it work for anyone else? Just do a echo
>> > 'line 0 0 10 10' > dev.file
>>
>> Haven't tried it, but I think that the problem is that you are updating  
>> the
>> UI from the "readthread". A good example to model your app after is  
>> here:
>>
>> http://effbot.org/zone/tkinter-threads.htm
>>
>> Peter
>
> Update: Not only is that a good model, its exactly what I'm trying to
> do.  Thanks again!

BTW, instead of reading the queue periodically, you can also use the event  
loop for that: in the secondary thread, generate a custom event using the  
event_generate method. Custom events are enclosed in '<<...>>', the '...'  
can be whatever you like. Be sure to generate the event with the  
when='tail' option or the event might get handled immediatly. To treat the  
event, do a binding on it: it will be called in your main thread. It's a  
common trick to switch threads so that GUI events are treated in the main  
thread and not in secondary ones.

Example:

------------------------------------------
import threading
import time
import Queue
 from Tkinter import *

root = Tk()

q = Queue.Queue()

def thread_action():
   i = 1
   while 1:
     time.sleep(1)
     q.put(i)
     root.event_generate('<<Ping>>', when='tail')
     i += 1

v = StringVar()

def ping_received(event):
   v.set(q.get())

Label(root, textvariable=v, width=10).pack()
root.bind('<<Ping>>', ping_received)

th = threading.Thread(target=thread_action)
th.setDaemon(1)
th.start()

root.mainloop()
------------------------------------------

HTH
-- 
python -c "print ''.join([chr(154 - ord(c)) for c in  
'U(17zX(%,5.zmz5(17l8(%,5.Z*(93-965$l7+-'])"