Ajax not working inside hook_field_widget_form()

Question

How to make ajax work inside hook_field_widget_form()

    /**
      * Implements hook_field_widget_form().
     */
        function test_field_widget_form($form, &$form_state, $field, $instance, $langcode, $items, $delta, $element) {
      $form_field['autocomplete'] = array(
        '#type' => 'textfield',
        '#title' => 'Tags',
        '#autocomplete_path' => 'taxonomy/autocomplete' . '/' . $field['field_name'],
        '#size' => $instance['widget']['settings']['size'],
        '#maxlength' => 1024,
        '#element_validate' => array('taxonomy_autocomplete_validate'),
        '#prefix' => '<div id ="subscribers-name">',
        '#suffix' => '</div>',
      );
      if (isset($form_state['values']['autocomplete'])) {
        $form_field['autocomplete']['#value'] = 'new value';
      }

      $form_field['search_tags'] = array(
        '#type' => 'button',
        '#value' => 'Recommend Tags',
        '#ajax' => array(
          'callback' => 'call_ajax_replace_value',
          'wrapper' => 'subscribers-name',
          'method' => 'replace',
        ),
      );
      $element += $form_field;
      return $element;
    }

    function call_ajax_replace_value($form, &$form_state) {
       return $form['field_tags'][LANGUAGE_NONE][0]['autocomplete'];
    }

How do i update autocomplete textfield value on AJAX callback?

Answer 1

Just assign the value in callback function.

/**
 * Implements hook_field_widget_form().
 */
function test_field_widget_form($form, &$form_state, $field, $instance, $langcode, $items, $delta, $element) {
  $form_field['autocomplete'] = array(
    '#type' => 'textfield',
    '#title' => 'Tags',
    '#autocomplete_path' => 'taxonomy/autocomplete' . '/' . $field['field_name'],
    '#size' => $instance['widget']['settings']['size'],
    '#maxlength' => 1024,
    '#element_validate' => array('taxonomy_autocomplete_validate'),
    '#prefix' => '<div id ="subscribers-name">',
    '#suffix' => '</div>',
  );

  $form_field['search_tags'] = array(
    '#type' => 'button',
    '#value' => 'Recommend Tags',
    '#ajax' => array(
      'callback' => 'call_ajax_replace_value',
      'wrapper' => 'subscribers-name',
      'method' => 'replace',
    ),
  );
  $element += $form_field;
  return $element;
}

function call_ajax_replace_value($form, &$form_state) {
  if (isset($form_state['values']['autocomplete'])) {
    $form_field['autocomplete']['#value'] = 'new value';
  }
  return $form['field_tags'][LANGUAGE_NONE][0]['autocomplete'];
}