buildGroupOptions example

/** * Displays the Build Group form. */
  public function buildGroupForm($form, FormStateInterface $form_state) {
    $item = &$this->options;
    // flip. If the filter was a group, set back to a standard filter.     $item['is_grouped'] = empty($item['is_grouped']);

    // If necessary, set new defaults:     if ($item['is_grouped']) {
      $this->buildGroupOptions();
    }

    $view = $form_state->get('view');
    $display_id = $form_state->get('display_id');
    $type = $form_state->get('type');
    $id = $form_state->get('id');
    $view->getExecutable()->setHandler($display_id, $type, $id, $item);

    $view->addFormToStack($form_state->get('form_key'), $display_id, $type, $id, TRUE, TRUE);

    $view->cacheSet();