C#ODP.NET调用Oracle函数返回值时报错的一个解决方案

CREATE OR REPLACE FUNCTION F_Update_Grade(v_UserID in Number)
 return nvarchar2 is
 V_Grade nVARCHAR2(20);
begin
 V_Grade := '1205';
 update TESTDB3 set Grade = V_Grade where PKID = v_UserID;
 commit;
 return (V_Grade);
end F_Update_Grade;

declare
 V_Result nvarchar2(1000) := '';
 V_UserID number(10) := 1;
begin
 V_Result := f_update_grade(V_UserID);
  dbms_output.put_line('Value:' || V_Result);
end;

/*
Value:1205
*/

using Oracle.ManagedDataAccess.Client;
using System;
using System.Data;
using System.Data.SqlClient;

namespace TestOracle_ManagedDataAccess
{
  class Program
  {
    static void Main(string[] args)
    {
      TestFUNCTION3();
      Console.ReadLine();
    }

    static void TestFUNCTION3()
    {
      string strConn = "Data Source=127.0.0.1/BCS;User ID=user2019;Password=password9102";
      //OracleConnection objConn = new OracleConnection(strConn);
      string strFun = "F_Update_Grade";
      //string strFun = "F_Get_Grade";
      using (OracleConnection objConn = new OracleConnection(strConn))
      {
        using (OracleCommand cmd = new OracleCommand(strFun, objConn))
        {
          try
          {
            // 获取选中行
            //int strRowIdex = 1;

            // 创建参数对象
            OracleParameter p1 = new OracleParameter("v_UserID", OracleDbType.Int32, ParameterDirection.Input);
            OracleParameter p2 = new OracleParameter("V_Grade", OracleDbType.NVarchar2, 20);
            p1.Value = 1;//取PKID为1的记录
            p2.Direction = ParameterDirection.ReturnValue;
            // 更新数据库表
            cmd.CommandType = CommandType.StoredProcedure;
            objConn.Open();

            /***************************************************************
             * 注意，输出参数一定要第一个加，函数的返回值也是赋给第一个参数*; 
             * *************************************************************/
            cmd.Parameters.Add(p1);
            cmd.Parameters.Add(p2);
            cmd.ExecuteNonQuery();

            //返回结果值
            Console.WriteLine("V_Grade is :" + p2.Value.ToString());
            Console.WriteLine("OK");
          }
          catch (SqlException ex)
          {
            objConn.Close();
            Console.WriteLine("ERROR in :" + ex.Message);
          }
          finally
          {
            cmd.Dispose();
            objConn.Close();
          }
        }
      }
    }

update testdb3 set grade=1 where PKID=1;