Prado\Web\UI\WebControls\TDataGridColumn::saveState PHP Method

    public function saveState()
    {
        return $this->_viewState;
    }

 /**
  * Saves items into viewstate.
  * This method overrides the parent implementation by saving list items
  */
 public function saveState()
 {
     $this->setViewState('Items', $this->_listControl->getItems()->saveState(), null);
     return parent::saveState();
 }