cscvrp has asked for the wisdom of the Perl Monks concerning the following question:

As part of a validatecommand for an entry widget I want to update a label widget as well as change the background color of the entry itself. I find that if I call update() on either the entry or label in the validating sub it will randomly stop working. The debug print statement in the sub stops, the background stops changing, the label stops getting updated, it sure seems to not be either being called or something is wedged. Everything else appears to work fine. I've extracted an example below. If I comment out the update() in inline_validate_section() it seems fine and works as desired, but the examples I followed (some from perlmonks) include update(), I'm curious to understand whats going on. The code below will take a few to a few dozen inputs before no longer validating..On older 586 class hardware this was written to run on it seems to fail very quickly, on my 2016 MBP it takes some rapid inputs, so it seems like maybe a timing thing. 
use Tk;

%mults = (
    A => "a",
    B => "b",
);

sub inline_validate_section {
    my $entry = uc(shift);
    print "$entry\n";
    if(defined($mults{$entry}) || !$entry){
        $Inputs{Section}->configure(-background => lightgrey);
        $Telltale{Section}->configure(-text => "$mults{$entry}");
        $Telltale{Section}->update();
    } else {
        $Inputs{Section}->configure(-background => red);
        $Telltale{Section}->configure(-text => "nope");
        $Telltale{Section}->update();
    }
    return 1;
}

 my $main = MainWindow->new();
 $main->geometry('400x100');

 # two frames and adjuster
 my $main_frame = $main->Frame; # right

  # pack frames
 $main_frame->pack(qw/-side right -fill both -expand l/);

     $vn = "Section";

  $main_frame->Label(-text => $vn, -width => 15)->pack(qw/-side left/)
+;
    $Inputs{$vn} = $main_frame->Entry(-validate        => 'key',
                    -validatecommand => [\&inline_validate_section],
                    -textvariable => \$$vn)->pack(qw/-side left -padx 
+10 -pady 5 -fill x/);

  $Telltale{$vn} = $main_frame->Label(-text => "nope", -width => 25)->
+pack(qw/-side left/);

 MainLoop();

[download]

Replies are listed 'Best First'.
Re: tk Entry validatecommand stops responding
by tybalt89 (Monsignor) on Nov 20, 2018 at 13:35 UTC

    Stopped failing for me once I commented out the two ->update calls. They were not needed anyways. 

    #!/usr/bin/perl

# https://perlmonks.org/?node_id=1226054

use strict;
use warnings;
use Tk;
$SIG{__WARN__} = sub { die @_ };

my %mults = (
    A => "a",
    B => "b",
    '' => '',
);
my %Inputs;
my %Telltale;

sub inline_validate_section {
    $Inputs{Section} or return 1;
    $Telltale{Section} or return 1;
    my $entry = uc(shift);
    print "$entry\n";
    if(defined($mults{$entry}) || !$entry){
        $Inputs{Section}->configure(-background => 'lightgrey');
        $Telltale{Section}->configure(-text => "$mults{$entry}");
        #$Telltale{Section}->update();
    } else {
        $Inputs{Section}->configure(-background => 'red');
        $Telltale{Section}->configure(-text => "nope");
        #$Telltale{Section}->update();
    }
    return 1;
}

 my $main = MainWindow->new();
 $main->geometry('400x100');

 # two frames and adjuster
 my $main_frame = $main->Frame; # right

  # pack frames
 $main_frame->pack(qw/-side right -fill both -expand l/);

     my $vn = "Section";

  $main_frame->Label(-text => $vn, -width => 15)->pack(qw/-side left/)
+;
    $Inputs{$vn} = $main_frame->Entry(-validate        => 'key',
                    -validatecommand => [\&inline_validate_section],
                    -textvariable => \$vn)->pack(qw/-side left -padx 1
+0 -pady 5 -fill x/);

  $Telltale{$vn} = $main_frame->Label(-text => "nope", -width => 25)->
+pack(qw/-side left/);

 MainLoop();

    [download]

    Notice other changes to run under strict and warnings :(

[reply]
[d/l]
      Thanks for looking at it, I'm curious as to why it does what it does with the ->update in there mostly, glad to see you get the same behavior though. Yes I stripped it down pretty far for the example, but your right it does not hurt to practice like you play.
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