string IDataErrorInfo.this[string columnName] { get { if (columnName == "FName") { if (this.fName == null) { return("Please enter reader's first name"); } else if (fName.Trim() == string.Empty) { return("First name is required"); } else if (this.fName.Length > 50) { return("First name must not exceed 50 characters"); } else if (isNumeric(this.fName)) { return("First name cannot contain numeric characters"); } } else if (columnName == "LName") { if (this.lName == null) { return("Please enter reader's last name"); } else if (this.lName.Trim() == string.Empty) { return("Last name is required"); } else if (this.lName.Length > 50) { return("Last name must not exceed 50 characters"); } else if (isNumeric(this.lName)) { return("Last name cannot contain numeric characters"); } } else if (columnName == "Id") { int entered_id, max_id = ReaderService.GetMaxId(); if (!int.TryParse(this.id, out entered_id)) { return("ID must be an integer"); } else { if (entered_id < 1) { return("ID must be at least 1"); } else if (entered_id > max_id) { return("ID must not excced " + max_id.ToString()); } } } return(null); } }