存储过程的输出参数返回null

Question

SqlParameter[] par1 = new SqlParameter[4]; 

par1[0] = new SqlParameter("@prefix", "TIN-CMP-"); 
par1[1] = new SqlParameter("@codeLength", "17"); 
par1[2] = new SqlParameter("@LastCode", ""); 
par1[3] = new SqlParameter("@retVal", SqlDbType.VarChar, 20); 
par1[3].Direction = ParameterDirection.Output; 
var data = SqlHelper.ExecuteNonQuery(this.ConnectionString, "Proc_GenerateID", par1); 

它不抛出任何异常，但返回空值，在SSMS即使程序工作正常

Answer 1

确保SqlHelper.ExecuteQuery正在执行存储过程后读取输出参数值。

例如

yourCommand.ExecuteNonQuery(); 
string retVal = yourCommand.Parameters["@retVal"].Value;