// item 被 drop 到了 borderDelete
private void borderDelete_Drop(object sender, DragEventArgs e)
{
// 从数据源中删除指定的 Employee 对象
Data1.Remove(_draggingEmployee);
Data2.Remove(_draggingEmployee);
_draggingEmployee = null;
// 在 borderDelete 放下了拖动项
Debug.WriteLine("Drop");
}