/**
* Add sorting direction
* @param ilFormPropertyGUI $element
*/
protected function initSortingDirectionForm(ilContainerSortingSettings $sorting_settings, $element, $a_prefix)
{
$direction = new ilRadioGroupInputGUI($this->lng->txt('sorting_direction'), $a_prefix . '_sorting_direction');
$direction->setValue($sorting_settings->getSortDirection());
$direction->setRequired(TRUE);
// asc
$asc = new ilRadioOption($this->lng->txt('sorting_asc'), ilContainer::SORT_DIRECTION_ASC);
$direction->addOption($asc);
// desc
$desc = new ilRadioOption($this->lng->txt('sorting_desc'), ilContainer::SORT_DIRECTION_DESC);
$direction->addOption($desc);
$element->addSubItem($direction);
return $element;
}