use warnings; 
use strict;
use Tk;
use Tk::DialogBox;

my $mw = MainWindow->new;
$mw->protocol('WM_DELETE_WINDOW' => \&myexit);

MainLoop;

sub myexit{
    my $db = $mw->DialogBox(-title => "Are you sure you want to exit?", -buttons => ['OK', 'Cancel']);
    my $answer = $db->Show;
    Tk::exit if $answer eq 'OK';
}