code: protected function resolveViewName()
      {
          $viewName = Yii::$app->request->get($this->viewParam, $this->defaultView);
  
          if (!is_string($viewName) || !preg_match('~^\w(?:(?!\/\.{0,2}\/)[\w\/\-\.])*$~', $viewName)) {
              if (YII_DEBUG) {
                  throw new NotFoundHttpException("The requested view \"$viewName\" must start with a word character, must not contain /../ or /./, can contain only word characters, forward slashes, dots and dashes.");
              } else {
                  throw new NotFoundHttpException(Yii::t('yii', 'The requested view "{name}" was not found.', ['name' => $viewName]));
              }
          }
  
          return empty($this->viewPrefix) ? $viewName : $this->viewPrefix . '/' . $viewName;
      }
docs: Resolves the view name currently being requested.
  
  @return string the resolved view name
  @throws NotFoundHttpException if the specified view name is invalid