Tk Entry not updating when textvariable changes

[smithbr]

Hi, I am just starting with Tk and I'll admit, I don't get a chance to write a lot of Perl. But, this seems very simple to me so I can't figure out why it won't work.

#!/usr/bin/perl -w 
use Tk; 
use strict;

my $text = "foo";

my $mw = MainWindow->new; 

my $button = $mw->Button(-text=>'Change entry', -command=>\&change)->p
+ack();
my $entry = $mw->Entry(-textvariable=>$text)->pack();

MainLoop;

sub change
{
    print "\$text before: $text\n";
    $text = "bar";
    print "\$text after: $text\n";
    $mw->update;
}

I assume I must be doing something really stupid because my entry never gets updated, but $text changes from the prints.

If I add $entry->configure(-textvariable=>$text) before the $mw->update() it works ok. However, all the documentation suggests if I use textvariable, changing the variable anywhere should magically update the widget text.

I searched around, but the similar problems I saw were much more complicated than this so I didn't get a lot of help from them.

Thanks.