Adding signal to Combobox

["Mike Martin" <redtux1 googlemail com>]

Is it possible to add a clicked signal to a combobox

ie: when I click the combobox it runs a sub before showing the list.

I have tried using button_prees_event in an enclosing eventbox but no joy

What I am trying to do is to update the list of the combobox from a
prefernce dialog

I have a button which works, but I would rather it be done automatically

sample

$opts_mod->signal_connect('clicked'=>sub{&opts($video_type);});

this runs

sub opts {
my ($video_type,$enc)= _;
my $model= $video_type->get_model;
$model->clear;
my $title='Select Encoding Type';
$video_type->append_text("$title");
foreach my $type (sort keys %options){
no strict 'refs';
if ($type ne  'dir' and $type ne 'feedback'){
$video_type->append_text($options{$type}[6]);

}
}
$video_type->set_active(0);
}

and works, but I just cant think how to do it automatically