此代码在调用ExecuteScalar时抛出NullReferenceException:
selectedPassengerID = 0; //sqlCommand command = GenericDataAccess.CreateCommand(); // 2nd test string connectionString = ""; sqlConnection conn; connectionString = ConfigurationManager. ConnectionStrings["ConnST-MHM"].ConnectionString; conn = new sqlConnection(connectionString); sqlCommand command = new sqlCommand(); command.CommandType = CommandType.StoredProcedure ; command.Connection = conn; command.CommandText = "SearchForPassenger"; sqlParameter param; param = command.CreateParameter(); param.ParameterName = "@name"; param.Value = pName; // Session[""]; param.DbType = DbType.String; command.Parameters.Add(param); param = command.CreateParameter(); param.ParameterName = "@flightDate"; param.Value = date; param.DbType = DbType.String; command.Parameters.Add(param); param = command.CreateParameter(); param.ParameterName = "@ticketNo"; param.Value = ticketNumber; param.DbType = DbType.Int32; command.Parameters.Add(param); int item; command.Connection.Open(); item = (int)command.ExecuteScalar();