如何从C#函数的存储过程返回多个输出参数

这是我的存储过程：

ALTER PROCEDURE [dbo].[sp_GetCustomerMainData] 
    -- Add the parameters for the stored procedure here
        @Reference nvarchar(100),@SubscriptionPIN nvarchar(100) OUTPUT,@SignupDate nvarchar(100) OUTPUT,@ProductCount int OUTPUT
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    SET @SubscriptionPIN = 'N/A'
    SET @SignupDate = 'N/A'
    SET @ProductCount = 0

    -- Insert statements for procedure here
    IF EXISTS(SELECT [SubscriptionPIN] FROM [Norton].[dbo].[Customers] WHERE [Reference] = @Reference)
    BEGIN
        SELECT TOP 1 @SubscriptionPIN = [SubscriptionPIN],@SignupDate = SignUpDate  FROM [Norton].[dbo].[ProductList] WHERE [Reference] = @Reference
        SET @ProductCount = (SELECT COUNT(*) FROM [Norton].[dbo].[ProductList] WHERE [Reference] = @Reference)
    END

    RETURN (@SubscriptionPIN)
    RETURN (@SignupDate)
    RETURN (@ProductCount)
END

我不确定最后的回报：

RETURN (@SubscriptionPIN)
RETURN (@SignupDate)
RETURN (@ProductCount)

另一方面,这是c#代码：

using (SqlConnection con = new SqlConnection(connectionInfo))
{
    using (SqlCommand cmd = new SqlCommand("sp_GetCustomerMainData",con) { CommandType = CommandType.StoredProcedure })
    {
        cmd.Parameters.Add("@Reference",SqlDbType.NVarChar).Value = CustomerReferenceID;

        SqlParameter SubscriptionPIN = new SqlParameter("@TheCustomerID",SqlDbType.NVarChar) { Direction = ParameterDirection.Output };
        cmd.Parameters.Add(SubscriptionPIN);

        SqlParameter SignupDate = new SqlParameter("@SignupDate",SqlDbType.NVarChar) { Direction = ParameterDirection.Output };
        cmd.Parameters.Add(SignupDate);

        SqlParameter ProductCount = new SqlParameter("@ProductCount",SqlDbType.Int) { Direction = ParameterDirection.Output };
        cmd.Parameters.Add(ProductCount);

        con.Open();

        try
        {
            cmd.ExecuteNonQuery();

            if (cmd.Parameters["@TheCustomerID"].Value.ToString() != "N/A")
            {
                aStatus.SubscriptionPIN = cmd.Parameters["@TheCustomerID"].Value.ToString();
                aStatus.SignupDate = cmd.Parameters["@SignupDate"].Value.ToString();
                aStatus.ProductCount = int.Parse(cmd.Parameters["@ProductCount"].Value.ToString());
                aStatus.Result = "0: Reference ID Found";
             }
             else
             {
                 aStatus.Result = "1: Reference ID does not exists";
                 return aStatus;
             }
          }
          catch (SqlException sqlExc)
          {
              foreach (SqlError error in sqlExc.Errors)
              {
                  aStatus.Result = string.Format("{0}: {1}",error.Number,error.Message);
                  return aStatus;
              }
          }
      }
}

当我运行此代码时,我收到错误：

System.InvalidOperationException: String[1]: the Size property has an invalid size of 0.
at System.Data.SqlClient.SqlParameter.Validate(Int32 index,Boolean isCommandProc)
at System.Data.SqlClient.SqlCommand.SetUpRPCParameters(_SqlRPC rpc,Int32 startCount,Boolean inSchema,SqlParameterCollection
parameters)
at System.Data.SqlClient.SqlCommand.BuildRPC(Boolean inSchema,SqlParameterCollection parameters,_SqlRPC& rpc)
at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior
cmdBehavior,RunBehavior runBehavior,Boolean returnStream,Boolean
async)
at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior
cmdBehavior,String
method,DbAsyncResult result)
at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult
result,String methodName,Boolean sendToPipe)
at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()

我不知道从存储过程发送许多输出参数的正确方法是什么,有人可以帮忙吗？