UPDATE:
I forgot about the '$mw->update;' commands that would need to go in there as well, so that the Cancel button press is seen. However, in the example script this is handled by the output sub.

Hello World!\n

Often when I'm creating Tk GUI based scripts, I include a Cancel button for the longer operations.

However, the only way I have found to make the cancel button work is to have many 'return if $cancel;' type commands interspersed all through the subroutine, which can get very tedious if the routine is quite long and complicated.

So, I was wondering, is there an easier way to get a subroutine to terminate?

Thanks,

Spike.

In the following simple example, as the loop is small, it's easy to include a 'return if $cancel;' command, but imagine that the start subroutine is a very long and complicated routine, without a simple loop structure. Then you've got to add 'return if $cancel;' over and over again.

use strict;
use warnings;
use Tk;
use Tk::ROText;
my $cancel = 0;

my $mw = MainWindow -> new (-title => "  loop test");
$mw -> withdraw;
$mw -> minsize (qw(700 400));

my $status = $mw -> Scrolled ("ROText",
            -scrollbars => 'e',
            -background => 'white',
            ) ->pack(
            -expand => 1,
            -fill => 'both',
            );

$status -> configure(-wrap => 'word');

my $exit = $mw -> Button (
            -text , 'Exit',
            -command, \&my_exit,
            ) -> pack (-side, 'left');

my $start = $mw -> Button (
            -text , 'Start',
            -command, \&start,
            ) -> pack (-side, 'right');

$mw -> Popup;
$mw -> focus;

MainLoop();

sub start {
    $cancel = 0;

    $start -> configure (
            -state => 'disabled',
            -relief => 'sunken');

    $exit -> configure (
            -text => 'Cancel',
            -command => \&cancel);

    for (1..100) {
#          last if $cancel;
           output ("$_\n");
           sleep 2;
    }
    done();
}

sub cancel {
    output ("Cancelling...\n");
    $cancel =1;
}

sub my_exit {
    exit();
}

sub done {
    $start -> configure (
            -state => 'normal',
            -relief => 'raised');
    $exit -> configure (
            -text => "Exit",
            -command => \&my_exit);

    output ("Done.\n");
}

sub output {
    my $text = $_[0];
    $status->insert('end', "$text");
    $status -> see ('end');
    $mw->update;
}
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