FormAjaxSubscriber::onView

public FormAjaxSubscriber::onView(GetResponseForControllerResultEvent $event)

public function onView(GetResponseForControllerResultEvent $event) {
  // To support an AJAX form submission of a form within a block, make the
  // later VIEW subscribers process the controller result as though for
  // HTML display (i.e., add blocks). During that block building, when the
  // submitted form gets processed, an exception gets thrown by
  // \Drupal\Core\Form\FormBuilderInterface::buildForm(), allowing
  // self::onException() to return an AJAX response instead of an HTML one.
  $request = $event->getRequest();
  if ($request->query->has(FormBuilderInterface::AJAX_FORM_REQUEST)) {
    $request->query->set(MainContentViewSubscriber::WRAPPER_FORMAT, 'html');
  }
}