Re^2: reset checkbutton value

Thank you AppleFritter.
Where exactly did I go wrong? Could you explain please? I had a look at the doc and seen that deselect would deselect the checkbuttons but I tried and no luck. I guess I was selecting the wrong element to reference.

I see what made the difference was the button sub.

my $connButton = $mw->Button(
    -text       => "Connect",
    -command    => sub {
        my @networks = grep { defined } @checkbox;
        if(@networks == 1) {
            say $networks[0];
        } else {
            say "Select one network, please.";
        }
    }
[download]

I didn't post with the original code, at least I dont think but here was my version of the checkbutton function. Essentially the same as yours.

        open my $FILE, '<', "ESSID", or die "Can't open file: $!";

my @lines = <$FILE>;

my @Sel;
my $i = 0;
my @Selected;
my $checkButton;
foreach my $n ( @lines ) {

        chomp $n;

                $checkButton =  $mw->Checkbutton( -text => "$n",
                                                  -onvalue => 1,
                                                  -offvalue => 0,
                                                  -command => sub{push
+(@Sel, $n)} && sub{ $Selected[$i] = defined $Selected[$i] ? undef : $
+n;},
                                                  -variable => \$Selec
+ted[$i], )->pack(   -side => 'top',
                                                                      
+                    -anchor => 'nw' );
        $i=$i+1;

}
[download]

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Re^3: reset checkbutton value by AppleFritter (Vicar) on Sep 09, 2014 at 23:19 UTC
Where you mostly went wrong, I think, was in only pushing to `@Sel` and not popping from it. In other words, if you clicked on a checkbox, you'd push its value to `@Sel`; and if you clicked it again to deselect it, you'd just push again. The list would grow longer and longer, and things would not work as intended. Meanwhile, this: `-command => sub{push(@Sel, $n)} && sub{ $Selected[$i] = defined $Selec +ted[$i] ? undef : $n;}` [download] most likely will not do what you may think; although you can use the `&&` operator on anonymous subroutine references (they're scalars, after all), they'll always be a true value, and the operator will return the last value evaluated, in this case the second reference (see C style Logical And in perlop). So the above line is really equivalent to `-command => sub{ $Selected[$i] = defined $Selected[$i] ? undef : $n;}` [download] Now, this IS fairly close to what I wrote, of course, but: You're not pushing to `@Sel` at all anymore, so the check if it's got one element on it will always fail. Your anonymous subroutines use the `$i` you declared outside the loop - and `$i` is 5 when the loop is done, so all your checkboxes will operate on `$Selected[5]`. I got around the latter by introducing a new variable inside the loop that holds the current value of `$i`; this goes out out of scope at the end of the loop body, so in the next loop iteration, a new variable with the same name is created, and each anonymous subroutine sees a different variable, one that keeps the right value of `$i`. (It's worth noting that even though the variables go out of scope, their duration does not end, as they're still visible to the anonymous subroutines.) This is perhaps a little difficult to wrap your head around at first. For more information on scope and duration, I'd recommend Mark Dominus's Higher Order Perl (available as a free PDF here, or a dead-tree edition here), pp. 71-76.	[reply] [d/l] [select]

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Re^3: reset checkbutton value
by AppleFritter (Vicar) on Sep 09, 2014 at 23:19 UTC

Where you mostly went wrong, I think, was in only pushing to @Sel and not popping from it. In other words, if you clicked on a checkbox, you'd push its value to @Sel; and if you clicked it again to deselect it, you'd just push again. The list would grow longer and longer, and things would not work as intended.

Meanwhile, this:

-command => sub{push(@Sel, $n)} && sub{ $Selected[$i] = defined $Selec
+ted[$i] ? undef : $n;}
[download]

most likely will not do what you may think; although you can use the && operator on anonymous subroutine references (they're scalars, after all), they'll always be a true value, and the operator will return the last value evaluated, in this case the second reference (see C style Logical And in perlop). So the above line is really equivalent to

-command => sub{ $Selected[$i] = defined $Selected[$i] ? undef : $n;}
[download]

Now, this IS fairly close to what I wrote, of course, but:

You're not pushing to @Sel at all anymore, so the check if it's got one element on it will always fail.
Your anonymous subroutines use the $i you declared outside the loop - and $i is 5 when the loop is done, so all your checkboxes will operate on $Selected[5].

I got around the latter by introducing a new variable inside the loop that holds the current value of $i; this goes out out of scope at the end of the loop body, so in the next loop iteration, a new variable with the same name is created, and each anonymous subroutine sees a different variable, one that keeps the right value of $i. (It's worth noting that even though the variables go out of scope, their duration does not end, as they're still visible to the anonymous subroutines.)

This is perhaps a little difficult to wrap your head around at first. For more information on scope and duration, I'd recommend Mark Dominus's Higher Order Perl (available as a free PDF here, or a dead-tree edition here), pp. 71-76.

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