public bool ValidHeaderData() { if (BankRec == null) { MessageBox.Show(strings.ReqBankAccountNo); return(false); } if (MainRowList.Any(r => string.IsNullOrWhiteSpace(r.MachineId))) { MessageBox.Show(strings.ReqMachineId); return(false); } var duplicatedMachineId = MainRowList.GroupBy(r => new { r.MachineId }).FirstOrDefault(x => x.Count() > 1); if (duplicatedMachineId != null) { MessageBox.Show(string.Format("Machine Id cannot be duplicated {0}", duplicatedMachineId.Key.MachineId)); return(false); } if (MainRowList.GroupBy(r => new { r.StoreIserial, r.IsDefault }).Where(r => r.Key.IsDefault).Select(r => r.Count()).Any(r => r > 1)) { MessageBox.Show("Store Can have one Default Machine"); return(false); } return(true); }