Tkinter check box behaviour - Windows / Linux discrepancy

[Gabriel Genellina]

At Thursday 9/11/2006 20:28, peter wrote:

>I've come across a weird difference between the behaviour of the
>Tkinter checkbox in Windows and Linux.  The issue became apparent in
>some code I wrote to display an image in a fixed size canvas widget. If
>a checkbox was set then the image should be shrunk as necessary to fit
>the canvas while if cleared it should appear full size with scrollbars
>if necessary.
>
>The code worked fine under Linux (where it was developed).  But under
>Windows, the first click in the checkbox did nothing, then subsequent
>clicks adjusted the size according to the PREVIOUS, not the current,
>checkbox state.
>
>I've isolated the problem in the code below, which shows a single
>checkbox and a label to describe its state. It works ok under Linux,
>but in Windows it is always one click behind.


>         self.chkTest=tk.Checkbutton(frmMain,text='Click
>me!',variable=self.intTest)
>
>         self.chkTest.bind('<ButtonRelease-1>',self.chkTest_click)

Your code works fine in Linux just by accident. The action of button 
widgets must be associated to "command"; as you see, when the mouse 
button is released, the associated variable might not have been updated.
Remove that bind call, and use:

         self.chkTest=tk.Checkbutton(frmMain,text='Click 
me!',variable=self.intTest, command=chkTest_click)

(Should work fine on every platform - I've just tested on Windows)
The command is fired after the mouse up event, and *only* if the 
previous mouse down was over the same widget. Your code doesn't work 
either if the user presses SPACE to toggle the button state; using 
"command" works fine in this case too.


-- 
Gabriel Genellina
Softlab SRL 

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