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  // AJAX behaviors need these data, so we add it back in #after_build.

  $form['#after_build'][] = 'views_exposed_form_ajax_enable';

}

/**

 * Checks whether the exposed form will use AJAX.

 *

 * Passes required form information removed in

 * views_form_views_exposed_form_alter().

 *

 * @param array $form

 *   The form being processed.

 * @param array $form_state

 *   The form state.

 *

 * @return array

 *   The form being processed.

 */

function views_exposed_form_ajax_enable(array &$form, array &$form_state) {

  // In order for AJAX to work the form build info is needed. Here check if

  // #ajax has been added to any form elements, and if so, pass this info as

  // settings via JavaScript, which get attached to the submitted form on AJAX

  // form submissions. #ajax property can be set not only for the first level of

  // the form, so look for it in the whole form.

  $ajax_info = array();

  $ajax_elements = views_exposed_form_ajax_lookup_recursive($form);

  // Determine if form is being processed.

  $triggering_element_name = '';

  if (!empty($form_state['input']['_triggering_element_name'])) {

    $triggering_element_name = $form_state['input']['_triggering_element_name'];

  }

  // When there are multiple elements with #ajax set on exposed form, pass only

  // triggering element name to JavaScript, otherwise #ajax will work only for

  // the first element.

  if (!empty($triggering_element_name) && !empty($ajax_elements)) {

    // Check if element has #ajax property set.

    if (in_array($triggering_element_name, $ajax_elements)) {

      $ajax_elements = array(

        $triggering_element_name => $triggering_element_name,

      );

    }

    else {

      $ajax_elements = array();

    }

  }

  if (!empty($ajax_elements)) {

    $form_info = array(

      'form_id' => $form['#form_id'],

      'form_build_id' => $form['#build_id'],

    );

    // Anonymous users don't get a token.

    if (!empty($form['#token'])) {

      $form_info['form_token'] = drupal_get_token($form['#token']);

    }

    foreach ($ajax_elements as $element_name) {

      $ajax_info[$element_name] = $form_info;

    }

    drupal_add_js(array('ViewsExposedFormInfo' => $ajax_info), 'setting');

    // Add the javascript behavior that will handle this data.

    $form['#attached']['js'][] = array(

      'weight' => 100,

      'data' => drupal_get_path('module', 'views') . '/js/exposed-form-ajax.js',

    );

  }

  return $form;

}

/**

 * Recursively looks for the #ajax property for every form elemet.

 *

 * @param array $elements

 *   The element array to look for #ajax property.

 *

 * @return array

 *   Array of the elements names where #ajax was found.

 */

function views_exposed_form_ajax_lookup_recursive(array $elements) {

  $ajax_elements = array();

  foreach (element_children($elements) as $key) {

    if (!empty($elements[$key]['#name']) && !empty($elements[$key]['#ajax'])) {

      $ajax_elements[$elements[$key]['#name']] = $elements[$key]['#name'];

    }

    // Recursive call to look for #ajax in element's childrens.

    $ajax_elements += views_exposed_form_ajax_lookup_recursive($elements[$key]);

  }

  return $ajax_elements;