To add a javascript onclick event on a form input with multiple checkbox, use this alternative method:
$options = array();
foreach($roles as $value => $label) {
$options[] = array(
'name' => $label,
'value' => $value,
'onClick' => 'showDiv(this)'
);
}
echo $form->input('Role', array('options' => $options, ...));
But why use inline javascript? You could do this with one line of mootools:
$('input[id^=ModelRole][type=checkbox]').addEvent('click', showDiv);
(replace 'Model' with the name of your model)
And I’m sure it’s just as easy (or easier) in jQuery or other frameworks.