submitExtraOptionsForm example

public function validateForm(array &$form, FormStateInterface $form_state) {
    $form_state->get('handler')->validateExtraOptionsForm($form['options'], $form_state);
  }

  /** * {@inheritdoc} */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $view = $form_state->get('view');
    $handler = $form_state->get('handler');
    // Run it through the handler's submit function.     $handler->submitExtraOptionsForm($form['options'], $form_state);
    $item = $handler->options;

    // Store the data we're given.     foreach ($form_state->getValue('options') as $key => $value) {
      $item[$key] = $value;
    }

    // Store the item back on the view     $view->getExecutable()->setHandler($form_state->get('display_id'), $form_state->get('type'), $form_state->get('id'), $item);

    // Write to cache