private void BtnAdd_Click(object sender, RoutedEventArgs e) { if (selected == null) { string name = txtName.Text; string author = txtAuthor.Text; string category = txtCategory.Text; string price = txtPrice.Text; string amount = txtAmount.Text; string idCategory = TheLoaiBUS.addCategory(category); string idAuthor = TacGiaBUS.addAuthor(author); SachDTO sach = new SachDTO(); sach.DonGia = price; sach.LuongTon = amount; sach.TenSach = name; sach.TenTacGia = idAuthor; sach.TenTheLoai = idCategory; int result = SachBUS.AddBook(sach); List <SachDTO> listBook = SachBUS.GetAll(); dtgBook.ItemsSource = listBook; dtgBook.Items.Refresh(); int Price = int.Parse(price); int Amount = int.Parse(amount); TotalCost += Price * Amount; lblTotal.Text = TotalCost.ToString(); } else { selected.LuongTon = txtAmount.Text; int Price = int.Parse(selected.DonGia); int Amount = int.Parse(selected.LuongTon); TotalCost += Price * Amount; lblTotal.Text = TotalCost.ToString(); int result = SachBUS.ChangeAmount(selected); if (result < 0) { MessageBox.Show("Thêm sách thất bại", "Lỗi", MessageBoxButton.OK, MessageBoxImage.Error); } } }