hi~
radGanttView1.GanttViewElement.DragDropService.PriviewDragStart += DragDropService_PreviewDragStart;
private void DragDropService_PreviewDragStart(object sender , PreviewDragStartEventArgs e)
{
GanttViewSummaryElement element = e.DragInstance as GanttViewSummaryElement;
if(element != null)
{
// Get Start and End
}
}