$obj->{ lb_class } =
    $f_class->Listbox( -selectmode => 'multiple',
		       -width => 30,
		       -height => 12,
		       -listvariable => $obj->{class}
     )->grid( -row => 0,-column => 0 );

  my $f_type = 
    $obj->{ "dlg" }->Frame( -relief => 'groove',
			    -borderwidth => 2
			  )->grid( -row => 1,
				   -column => 1 );

  $obj->{ type } = [( ...)];

  $obj->{ lb_type } =
    $f_type->Listbox( 
      -selectmode => 'multiple',
      -width => 30,
      -height => 12,
      -listvariable => $obj->{type} 
   )->grid( -row => 0,
            -column => 0 );