code: public function run()
      {
          $viewName = $this->resolveViewName();
          $this->controller->actionParams[$this->viewParam] = Yii::$app->request->get($this->viewParam);
  
          $controllerLayout = null;
          if ($this->layout !== null) {
              $controllerLayout = $this->controller->layout;
              $this->controller->layout = $this->layout;
          }
  
          try {
              $output = $this->render($viewName);
  
              if ($controllerLayout) {
                  $this->controller->layout = $controllerLayout;
              }
  
          } catch (InvalidParamException $e) {
  
              if ($controllerLayout) {
                  $this->controller->layout = $controllerLayout;
              }
  
              if (YII_DEBUG) {
                  throw new NotFoundHttpException($e->getMessage());
              } else {
                  throw new NotFoundHttpException(
                      Yii::t('yii', 'The requested view "{name}" was not found.', ['name' => $viewName])
                  );
              }
          }
  
          return $output;
      }
docs: Runs the action.
  This method displays the view requested by the user.
  @throws NotFoundHttpException if the view file cannot be found