Re: Tk::Scale, how to avoid callback when displayed?

[Khen1950fx]

That's normal behavior because the callback is called when the widget is first created and when each value is changed. The trick is to keep the callback down to the fewest possible values; hence the value can be modified by user interaction just like other widgets. Using an example from the source:

#!/usr/bin/perl 

use strict;
use warnings;
use Tk;

my $top = MainWindow->new();
$top->title("scale tests");

my $f = $top->Frame(
    -relief => 'ridge', 
    -borderwidth => 3,
);

my $s = $top->Scale(
    "-orient" => "horizontal",
    "-length" => 300,
    "-from"   => 0,
    "-to"     => 250,
    "-tickinterval" => 25,
    "-command" => sub {
        my $s; 
        $f->configure(
            '-width' => $s->get
        ) 
    }
);

$s->pack(-side => 'left',  -fill => 'y');
$f->pack(-side => 'right', -fill => 'y');

Tk::MainLoop;

[perltux]

I don't quite understand the example code and how it relates to my problem. I tried running it but even your example invokes the command when the scale is first displayed before any user interaction (which is what I would like to avoid).

[golux]

Hi perltux,

Would it be satisfactory to simply ignore the first call?

Using the example Khen1950fx gave (and fixing the scoping issue with $s) you could do it like this:

#!/usr/bin/perl 

use strict;
use warnings;
use Tk;

my $top = MainWindow->new();
$top->title("scale tests");

my $f = $top->Frame(
    -relief => 'ridge', 
    -borderwidth => 3,
);

my $s;
$s = $top->Scale(
    "-orient" => "horizontal",
    "-length" => 300,
    "-from"   => 0,
    "-to"     => 250,
    "-tickinterval" => 25,
    "-command" => sub {
        use feature 'state';
        state $ncalls++ or return;
        printf "Callback: Scale(%d)\n", $_[0];
        $f->configure(
            '-width' => $s->get
        ) 
    }
);

$s->pack(-side => 'left',  -fill => 'y');
$f->pack(-side => 'right', -fill => 'y');

Tk::MainLoop;

[perltux]

Thanks that could be a viable workaround, I will look into it.