code: public function run()
      {
          if (!empty($this->_fields)) {
              throw new InvalidCallException('Each beginField() should have a matching endField() call.');
          }
  
          $id = $this->options['id'];
          $options = Json::encode($this->getClientOptions());
          $attributes = Json::encode($this->attributes);
          $view = $this->getView();
          AdminUiActiveForm::register($view);
          $view->registerJs("jQuery('#$id').yiiActiveForm($attributes, $options);");
  
          echo Html::endForm();
      }
docs: Runs the widget.
  This registers the necessary javascript code and renders the form close tag.
  @throws InvalidCallException if `beginField()` and `endField()` calls are not matching