/**
  * Create activity.
  */
 public function actionCreate()
 {
     $model = new Activity(['scenario' => 'create']);
     Yii::$app->response->format = Response::FORMAT_JSON;
     if ($model->load(Yii::$app->request->post())) {
         if ($model->validate()) {
             if ($model->save(false)) {
                 return $this->tree($model);
             } else {
                 Yii::$app->response->setStatusCode(500);
                 return \Yii::t('net_frenzel_activity', 'FRONTEND_FLASH_FAIL_CREATE');
             }
         } elseif (Yii::$app->request->isAjax) {
             Yii::$app->response->setStatusCode(400);
             return ActiveForm::validate($model);
         }
     }
 }