It's my opinion that you are using DialogBox incorrectly by not having any buttons.

If you are always putting GUIask in a DialogBox, I would do it this way. If not, please provide a more extensive sample program.

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11141756
use warnings;
use Tk;
use Tk::DialogBox;
use Tk::Frame;

{ ## OPEN package

package Tk::GUIask;

use List::Util qw(first);
use base qw/Tk::Frame  /;

Construct Tk::Widget 'GUIask'; ## INSTALL MyNewWidget in pTk namespace

sub ClassInit  ## Called once to intitalise new class
  {
  my ($class , $mw ) = @_;
  $class ->SUPER::ClassInit($mw);
  }

sub Populate
  {
  my ($self , $args   ) = @_;
  $self ->SUPER::Populate($args) ;

  my $search = "";

  my $frame = $self -> Frame( -borderwidth => 5, -relief => 'ridge',
    ) -> pack();

  my $label = $frame -> Label ( -fg => 'blue', -font => 30
    ) -> pack(-fill => 'x'  );

  my $entry = $frame -> Entry(
    ) -> pack(-fill => 'x');

  $self -> Advertise ('entry' => $frame );
  $self -> ConfigSpecs (
    DEFAULT => [$frame],
    textvariable => [$entry], # NOTE
    text => [$label]
    );

  $self -> Delegates ( DEFAULT => $frame,
    bind => $entry,
    );

  } ## CLOSE Populate

1;

} ## CLOSE package

##       Invoke the MEGAWIDGET down here to test       ##

my $mw = MainWindow -> new;
$mw -> geometry('300x300+900+250');
$mw -> title('Main Window ');

my $header_msg ="FOOOOO";
my $input = '';

my $dialog = $mw ->DialogBox( -title => ' ', -buttons => [qw(OK Abort)
+]);

my $entry = $dialog -> GUIask(
  -textvariable => \$input,
  -text => $header_msg
  )-> pack();

my $reply = $dialog->Show; # NOTE
$reply eq 'OK' and print "input = $input\n";

MainLoop;
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