Create dependent dropdown in views exposed filter
I haven't check but 

{
  $form['computer_stats']['os'] = array(
    '#title' =&gt; t('Operating system'),
    '#type' =&gt; 'select',
    '#options' =&gt; drupal_map_assoc(array('', t('OSX'), t('Linux'), t('Windows'))),
    '#ajax' =&gt; array(
      'callback' =&gt; 'input_os_verify_ajax_callback',
      'wrapper' =&gt; 'input_os_verify_wrapper',
     ),
  );

  // Setting an empty element with a wrapper to be populated.
  $form['computer_stats']['os_verify'] = array(
    '#type' =&gt; 'markup',
    '#prefix' =&gt; '&lt;div id="input_os_verify_wrapper"&gt;',
    '#suffix' =&gt; '&lt;/div&gt;',
  );

  // When submitted, check for value of OS, and populate os_verify.
  if (isset($form_state['values']['os'])) { // Fixed this line, was throwing an error in the original video code.
    $form['computer_stats']['os_verify']['#type'] = 'checkbox';
    $form['computer_stats']['os_verify']['#title'] = t('Are you sure you are using @os?', array('@os' =&gt; $form_state['values']['os']));
  }

  ...
}


function input_os_verify_ajax_callback($form, $form_state) {
  return $form['computer_stats']['os_verify'];
}


from How to Build Beautiful Forms in Drupal 7 (Video Presentation) might help