private void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
 {
     RaisePropertyChanged(e.PropertyName);
     if (e.PropertyName == "Amount")
     {
         TotalAmount = MainRowList.Sum(x => x.Amount);
     }
     if (e.PropertyName == "Qty")
     {
         TotalQty = MainRowList.Sum(x => x.Qty);
     }
 }