private void rbBulk_Checked(object sender, RoutedEventArgs e)
 {
     if (!isInitialized)
         return;
     _vm = DataContext as POSLineItemViewModel;
     _vm.LineItemType = Lib.UI.Hierarchy.LineItemType.Bulk;
     _vm.ChangeAvailableQty();
     _vm.RecalcTotal();
 }