public void LoadPaymentDetailFromDB() { List <PaymentDetail> paymentDetail = new List <PaymentDetail>(); paymentDetail.Clear(); List <string> rooms = new List <string>(); rooms.Clear(); rooms.AddRange(RentInfo.GetRoomNameByCustomerID(((Customer)cbCustomerName.SelectedItem).IdCardNumber)); foreach (var item in rooms) { paymentDetail.AddRange(PaymentDetail.GetPaymentDetailByRoomName(item)); } paymentDetails.Clear(); foreach (var item in paymentDetail) { paymentDetails.Add(item); } }