code: public function renderItems()
      {
          $models = $this->dataProvider->getModels();
          $keys = $this->dataProvider->getKeys();
          $rows = [];
          foreach (array_values($models) as $index => $model) {
              $key = $keys[$index];
              if (($before = $this->renderBeforeItem($model, $key, $index)) !== null) {
                  $rows[] = $before;
              }
  
              $rows[] = $this->renderItem($model, $key, $index);
  
              if (($after = $this->renderAfterItem($model, $key, $index)) !== null) {
                  $rows[] = $after;
              }
          }
  
          return implode($this->separator, $rows);
      }
docs: Renders all data models.
  @return string the rendering result