zend addElements form onchange select - forms

Question

I try to add dinamically a form input Elemnt on onchange of select element.
I have this code:
$this->addElement('select', 'nationality', array(
'multiOptions' => array('CH' => 'Choose','IT' => 'Italy', 'other' => 'Other'),
'required' => true,
'label' => 'Nation',
'filters' => array('StringTrim'),
'onChange' => '???'
));
I try to paste my new element instead "???"
$this->addElement('select', 'nationality', array(
'multiOptions' => array('CH' => 'Choose','IT' => 'Italy', 'other' => 'Other'),
'required' => true,
'label' => 'Nation',
'filters' => array('StringTrim'),
'onChange' => '$this->addElement(
'text', 'codice_fiscale', array(
'required' => true,
'label' => 'Codice fiscale',
'required' => true
))'
));
I know is not correct, but I dont' found any documentation about it.
How can I add an element onchange select value?
Thanks in advance

Answer 1

I would approach the problem in a different way, if it's possible for you:
javascript functions to call on the onChange. It would be syntax correct (and, as you said, what you wrote is not correct, it's going to be printed out entirely on the onChange attribute, not interpreted through php).
so, i would write
'onChange' => 'addElement()'
and then declare the javascript function which handles new elements. Or, you can prepare the elements before (if you have a fixed number), and show / hide them. It may be convenient if you don't have much elements, but if they're too many, just add through javascript the needed one.
PseudoCode Javascript
function addElement()
{
// add your element here, or show / hide it
}
As far as I saw from my experience and similar cases
(Zend_form_element_select onchange in zend framework,
Zend Form: onchange select load another view content)
you won't escape from Javascript if you want to handle the "onChange"