Tkinter: update_idletasks

[Jeffrey Barish]

Eric Brunel wrote:

> Jeffrey Barish wrote:
>> I'm confused about how to use the update_idletasks method.  In my
>> program, I have a handler for a button in which execution will
>> linger. During that time, I would like for the GUI to continue to
>> show signs of
>> life.  I have a Pmw MessageBar in which I display a status message. 
>> I figured out that if I run update_idletasks on that MessageBar, then
>> the
>> MessageBar will update the display as I update the message.  However,
>> if I cover the GUI with some other window and then expose it again,
>> the GUI does not refresh until the handler finishes (except for the
>> MessageBar).  Do I have to run the update_idletasks method for every
>> widget in the GUI?  for all the frames? for just the root frame?  Or
>> is it impossible to get the GUI to refresh in this situation?
> 
> At tcl level, update_idletasks isn't a "method", i.e. the tcl command
> doesn't take any parameter telling which widget to refresh. So calling
> the Tkinter update_idletasks method on any widget has exactly the same
> effect, which is to refresh the whole GUI.
> 
> There are some issues on Windows however, where the newly created
> toplevel's may not refresh until full control is returned to the GUI.
> To work around this problem, use the wait_visibility method to wait
> until the newly created window is displayed. But be careful:
> wait_visibility processes events, unlike update_idletasks that does
> just a GUI refresh. There is apparently no simple way of updating the
> display of newly created toplevel's on Windows without returning full
> control to the GUI (at least with tk/Tkinter)
> 
> I never saw the problem you describe (some windows refreshing, some
> not), but I mainly develop on Linux, which may show a different
> behaviour than the platform you're working on (which BTW you don't
> mention...). Maybe you can post a small piece of code showing the
> problem?
> 
> HTH
Ah.  I had a hunch that might be the case.  However, that is not the
behavior that I am seeing.  First, in response to your questions: (1) I
am on Linux (there are other platforms?); (2) I am using Python 2.3;
(3) it is difficult to extract a piece of the code, but I will attempt
to describe more clearly what I am doing.  There is a button with a
handler.  In the handler I use popen3 to launch a program that takes a
long time to execute.  I monitor its progress in a while loop by
reading a status line that it produces on stderr.  The status line
provides information about percentage complete; I use that information
to update the MessageBar in my GUI.  When the status line indicates
that the process is done, I exit the while loop and return from the
button handler.  I tried running update_idletasks on the MessageBar in
the while loop.  I tried running it on the root window, even though the
information you provided indicated that it doesn't matter what class
owns the method -- and my experience certainly does not contradict that
statement.  In every case, only the MessageBar updates.  Well, that's
not entirely true.  I also move a tag in a text widget; the previously
and newly tagged text redraws.  The only technique I have found that
permits the main window to update is to run most of the handler in a
separate thread.  The problem I am having with that approach is that
the MessageBar then flashes in an annoying way (the background seems to
go to white at every update and then gets redrawn to gray -- which
happens only when the while loop is in its own thread).  Any other
thoughts would be much appreciated.
-- 
Jeffrey Barish