exposed-collapsible--alter.php

<?php 
/**
 * Implements hook_form_FORM_ID_alter().
 *
 * Alter views exposed forms for collapsible filters.
 */
function MYMODULE_form_views_exposed_form_alter(&$form, &$form_state) {
  if (empty($form_state['view']) || !in_array($form_state['view']->name, array('NAME_OF_VIEW', 'NAME_OF_VIEWS_DISPLAY'))) {
    // We alter the exposed form of a single views display, so return if this is
    // not the expected view.
    return;
  }

  if (isset($form['type'])) {
    // Add option to select all items (equals to resetting the filter).
    $options = array(
      'All' => variable_get('views_exposed_filter_any_label', 'new_any') == 'old_any' ? t('<Any>') : t('- Any -'),
    );
    $options += $form['type']['#options'];
    // Change size of field based on number of options (max: 5 items).
    $form['type']['#size'] = min(array(count($options), 5));

    if (count($options) <= 2) {
      // Hide filter if there is only one option available (additional 
      // to "All").
      $form['type']['#access'] = FALSE;
    }
    $form['type']['#options'] = $options;
  }
  

  // Alter multi-value dropdowns.
  $form_multiple_selects = array();
  foreach (element_children($form) as $element_name) {
    if (isset($form[$element_name]['#type']) && $form[$element_name]['#type'] == 'select' && !empty($form[$element_name]['#multiple'])) {
      $form_multiple_selects[$element_name] = array(
        'size' => isset($form[$element_name]['#size']) ? $form[$element_name]['#size'] : 5,
      );
    }
  }
  if (count($form_multiple_selects)) {
    $form['#attached'] += array(
      'js' => array(), 
      'css' => array(),
    );
    // Attach custom javascript to the form.
    $form['#attached']['js'][] = drupal_get_path('module', 'MYMODULE') . '/js/MYMODULE.admin.js';
    $form['#attached']['js'][] = array(
      'data' => array(
        'collapsibleFilter' => array(
          'multiple_selects' => $form_multiple_selects,
        ),
      ),
      'type' => 'setting',
    );
  }
}
?>