<OT> tcl/tk question: Radio buttons

[Roger Oberholtzer]

A checkbutton wants a boolean variable. You have assigned a string to a
variable, resulting in a non-boolean being attached to the radio button. 

I seem to always use checkbutton with the variable statement. A radiobutton
is a boolean thing, so the variable indicating it's state should be boolean
in nature.

If you want a command to be called when the variable changes state (either
because the radio button was used) or because you set it to the desired
boolean directly, use the trace command:

	trace add variable cb w {my script}

Then, whenever 'cb' is written to, {my script} is executed. This is a very
powerful feature of Tcl.

On Sun, 21 Dec 2003 20:12:49 -0500
Joel Hammer <joel at hammershome.com> wrote:

> I just want to get this point cleared up before I go off in the wrong
> direction.
> 
> I have found if I change the global variable (-variable) associated with
> a checkbutton, the button stops responding.
> 
> I have included a program snippet below, as I think you can't have
> attachments on this list.
> 
> Basically, when I click a radio button, and run a command like 
> 
>      -command {puts "string"}
> 
> all works as expected. However, if I change the radiobutton option
> -variable in the command, with something like:
> 
>      -command {set cb "You ran a program"}

Be aware that 'cb' in this context will by default be a global variable. If
you want to access it in a proc, add this to the beginning of the proc:

		global cb

> 
> the radio button stops responding. cb is my -variable in this radiobutton.
> 
> It makes no difference if I remove the -onvalue and -offvalue options.
> 
> Is this a bug or a feature or am I missing something?
> 
> Thanks,
> 
> Joel
> 
> 
> #!/etc/alternatives/wish -f
> frame .myframe2
> pack .myframe2 -anchor w
> 
> # The command in the next line is the problem
> checkbutton .myframe2.cb -text "Choice 2" -onvalue True -offvalue False
> -variable cb -command {set cb "You ran a program"}
> 
> # This next line works fine
> # checkbutton .myframe2.cb -text "Choice 2" -onvalue True -offvalue False
> -variable cb -command {puts "You changed me"}

#2 works because you did not change 'cb' into a string variable by assigning
it a "string" value, as you did in #1.


> label .myframe2.lcb -textvariable cb 
> pack .myframe2.cb .myframe2.lcb -side left 
> 
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