#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $tl;
my $mw = MainWindow->new;
$mw->title( "MainWindow" );

my $spawn_button = $mw->Button( -text => "Toplevel", 
                -command => \&do_Toplevel )->pack();

MainLoop;

sub do_Toplevel {
        $spawn_button->configure(-state=>'disabled');

    if ( !Exists( $tl ) ) {
        $tl = $mw->Toplevel();
        
        $tl->protocol('WM_DELETE_WINDOW' => sub {
                     print "do nothing here\n"; #prevents destruction 
+of $tl
                                        #by WM control
         });
        
        $tl->geometry('300x100+100+100');
        $tl->title( "Toplevel" );
        $tl->Button(
            -text    => "Close",
            -command => sub { $tl->withdraw; 
                 $spawn_button->configure(-state=>'normal');
                 }
        )->pack;
    }
    else {
        $tl->deiconify();
        $tl->raise();
    }
}
[download]

#!/usr/bin/perl
use warnings;
use strict;
use Tk;


my $mw = MainWindow->new;
$mw->title( "MainWindow" );

my $spawn_button = $mw->Button( -text => "Toplevel", 
                -command => \&do_Toplevel )->pack();

my $change_button = $mw->Button( -text => "Toplevel repacked", 
                -command => \&do_Toplevel_repack )->pack();

######### make a top level withdrawn ##################
# make $tl global so it's memory space is reused
my $tl = $mw->Toplevel();
$tl->protocol('WM_DELETE_WINDOW' => sub {
         print "do nothing here\n"; #prevents destruction of $tl
                                #by WM control
  });
        
$tl->geometry('300x300+100+100');
$tl->title( "Toplevel" );
$tl->Button(
    -text    => "Close",
    -command => sub { $tl->withdraw; 
        $spawn_button->configure(-state=>'normal');
        $change_button->configure(-state=>'normal');
     })->pack();

$tl->withdraw;


MainLoop;

sub do_Toplevel {
        $spawn_button->configure(-state=>'disabled');
        $change_button->configure(-state=>'disabled');
        $tl->deiconify();
        $tl->raise();
}

sub do_Toplevel_repack {
        $spawn_button->configure(-state=>'disabled');
        $change_button->configure(-state=>'disabled');
    
    #clean out top level
    my @w = $tl->packSlaves;
    foreach (@w) { $_->packForget; }

        $tl->title( "Toplevel repack" );
        $tl->geometry('300x500+100+100');
        $tl->Button(
    -text    => "Close1",
    -command => sub { $tl->withdraw; 
           $spawn_button->configure(-state=>'normal');
           $change_button->configure(-state=>'normal');
        })->pack();

         my $text = $tl->Scrolled('Text')->pack();
    
         for (1..100){
        $text->insert('end', "$_\n");
        $text->see('end');
    }

     #add whatever widgets you want here
     # Entries, etc

        $tl->Button(
    -text    => "Add button to mainwindow",
    -command => sub { 
        $mw->Button(-text=>'new Button')->pack(-side =>'bottom');
    })->pack();

    
    $tl->deiconify();
    $tl->raise();
}
[download]