$goMainWindow = new MainWindow;
  $goMainWindow->geometry('200x300'); #Exit is lopped off

##</code><code>##

# at ther end of your build_gui sub

$goMainWindow->idletasks;
my $w = $goMainWindow->reqwidth;
my $h = $goMainWindow->reqheight; 
print "$w $h\n";
$goMainWindow->minsize($w,$h);

##</code><code>##

#!/usr/bin/perl
use strict;
use Tk;
require Tk::Pane;

our ($goMainWindow);
our (%ghGuiObjs);
our (%ghGuiCBVars);

$| = 1;
&main();

sub main {
  buildGui();
  MainLoop;
} #end sub main


sub updateA {
  if ( $ghGuiCBVars{"nEnableFrameA"} == 1 ) {
    $ghGuiObjs{"oContainerA"}->pack(
                          -expand => '1',
                          -fill => 'both',
                          -pady => '5',
    );

  } else {
    $ghGuiObjs{"oContainerA"}->packForget();
  }
}

sub updateB {
  if ( $ghGuiCBVars{"nEnableFrameB"} == 1 ) {
    $ghGuiObjs{"oContainerB"}->pack(
                          -expand => '1',
                          -fill => 'both',
                          -pady => '5',
    );
  } else {
    $ghGuiObjs{"oContainerB"}->packForget();
  }
}

sub buildGui {
  $goMainWindow = new MainWindow;
 
  my $mf =  $goMainWindow->Scrolled('Pane',
              -scrollbars => 'osoe',
               )->pack(
                      -expand => '1',
                      -fill => 'both',
                      -pady => '5',
                );


  my ($oLabel) = $mf->Label(
                      -text => "This is my example",
                      )->pack(
                      -padx => '5',
                      -pady => '5',
                      -expand => '1',
                      -fill => 'x',
                      );
  my ($oCbA) = $mf->Checkbutton(
                      -text => 'Enable A',
                      -variable => \$ghGuiCBVars{"nEnableFrameA"},
                      -command => \&updateA,
                      -anchor => 'w',
                     );
  $ghGuiCBVars{"nEnableFrameA"} = 1;
  
  my ($oFrameA) = $mf->Labelframe(
                      -labelwidget => $oCbA,
                      )->pack(
                      -padx => '5',
                      -expand => '1',
                      -fill => 'both',
                      );
  
  my ($oContainerFrameA) = $oFrameA->Frame(
                      )->pack(
                      -expand => '1',
                      -fill => 'both',
                      -pady => '5',
                      );
  $ghGuiObjs{"oContainerA"} = $oContainerFrameA;
  
  my ($oLbA) = $oContainerFrameA->Listbox(
                      -relief => 'groove',
                      -borderwidth => '5',
                      -height => '5',
                      )->pack(
                      -fill => 'both',
                      -expand => '1',
                      );


  my ($oCbB) = $mf->Checkbutton(
                      -text => 'Enable B',
                      -variable => \$ghGuiCBVars{"nEnableFrameB"},

                      -command => \&updateB,
                      -anchor => 'w',
                     );
  $ghGuiCBVars{"nEnableFrameB"} = 1;
  my ($oFrameB) = $mf->Labelframe(
                      -labelwidget => $oCbB,
                      )->pack(
                      -padx => '5',
                      -expand => '1',
                      -fill => 'both',
                      );
  my ($oContainerFrameB) = $oFrameB->Frame(
                      )->pack(
                      -expand => '1',
                      -fill => 'both',
                      -pady => '5',
                      );
  $ghGuiObjs{"oContainerB"} = $oContainerFrameB;
  my ($oLbB) = $oContainerFrameB->Listbox(
                      -relief => 'groove',
                      -borderwidth => '5',
                      -height => '5',
                      )->pack(
                      -fill => 'both',
                      -expand => '1',
                      );

  my ($oExit) = $goMainWindow->Button(-text => 'Exit',
                      -command => sub{exit},
                     )->pack(
                      -padx => '5',
                      -pady => '5',
                      -side => 'bottom',
                     );
  
}