Drupal Form APi Checkbox states - ajax

Question

So I have create my checkbox in my form
$form['existing_customer'] = array(
'#type' => 'checkbox',
'#title' => t('Are you an existing customer'),
'#ajax' => array(
'callback' => 'checkbox_selected',
'wrapper' => 'subject',
),);
This calls my function and changes the values in my checkbox
The problem is I cannot get it to switch back if it is unchecked
function checkbox_selected(&$form, &$form_state) {
if ($form_state['values']['existing_customer'] == 1) {
$my_options = array( 'select' => t('Select'), 'mr' => t('Mr'), 'mrs' => t('Mrs'), 'miss' => t('Miss'), 'ms' =>t('Ms'), 'sir' =>t('Sir'), 'dr' => t('Dr'), 'prof' => t('Prof') );
}
elseif ($form_state['values']['existing_customer'] == 0){
$my_options = array( 'seconfZ' => t('jimmy'), 'mr' => t('Mr'), );
}
$form['subject'] = array(
'#type' => 'select',
'#title' => t('Subject'),
'#options' => $my_options//$form['subject_options']['#value']
);
return $form['subject'];
}
I thought I could do a switch on the checkbox value or state but no joy?

Answer 1

Oftentimes, when you use the Form API #ajax system, the wrapper that you specify is actually replaced with another element AFTER drupal_html_id() has been called again on the element wrapper. So I would check the markup of the "subject" element in Firebug/Web Inspector after your AJAX stuff happens--I'm betting that the wrapper div is now something like "subject--1".
To fix this, you need to manually set a wrapper div on the item you are replacing--one that won't change when the form is rebuilt. For example, in your form builder:
$form['existing_customer'] = array(
'#type' => 'checkbox',
'#title' => t('Are you an existing customer'),
'#ajax' => array(
'callback' => 'checkbox_selected',
'wrapper' => 'subject-wrapper',
),
);
$form['subject'] = array(
'#prefix' => '<div id="subject-wrapper">',
...
`#suffix' => '</div>',
);
Hope that helps!