/**
* Returns the viewstate of this control and its children.
* This method is overriden to save the items data in view state,
* as well as the mapping between indexes and text/value pairs for
* the list items.
* @return array|null viewstate to be saved
*/
public function saveViewState()
{
if ($this->items->length() > 0) {
$this->setViewState('Items', $this->items);
}
return parent::saveViewState();
}