为何Balance获取不到参数？

[bg8crv]

 public bool UpDateFee(Fee _fee, string SqlConnStr)
        {
            string Balance = "@Balance";
            Balance = _fee.Balance;
            conn = new SqlConnection(SqlConnStr);
            conn.Open();
            cmd = new SqlCommand("UPDATE User_Account SET Balance=Balance-@Balance WHERE RFID=@RFID", conn);
            cmd.Parameters.Add(new SqlParameter("@Balance",SqlDbType.Money,8));
            cmd.Parameters.Add(new SqlParameter("RFID",_fee.RFID));
            if (cmd.ExecuteNonQuery() > 0)
            {
                conn.Close();
                return true;
            }
            else
            {
                conn.Close();
                return false;
            }
        }

SQL老提示@Balance获取不到参数，请问怎么修改呢？小妹实在没辙了.......

[zzyhuian06142]

cmd.Parameters.Add(new SqlParameter("@Balance",SqlDbType.Money,8));
cmd.Parameters.Add(new SqlParameter("RFID",_fee.RFID));
该成
cmd.Parameters.Add(new SqlParameter("@Balance",SqlDbType.Money));
cmd.Parameters["Balance"].Value = 5;
cmd.Parameters.Add(new SqlParameter("@RFID",SqlDbType.Int32));
cmd.Parameters["@RFID"] = _fee.RFID;看看

[zzyhuian06142]

还有你的表中应该是有存在一列叫Balance吧

[hongqi162]

 public bool UpDateFee(Fee _fee, string SqlConnStr)
        {
            string Balance = "@Balance";
            Balance = _fee.Balance;
            conn = new SqlConnection(SqlConnStr);
            conn.Open();
            cmd = new SqlCommand("UPDATE User_Account SET Balance=Balance-@Balance WHERE RFID=@RFID", conn);
            cmd.Parameters.AddWithValue("@Balance", Balance); 
            cmd.Parameters.AddWithValue("@RFID", _fee.RFID); 
            if (cmd.ExecuteNonQuery() > 0)
            {
                conn.Close();
                return true;
            }
            else
            {
                conn.Close();
                return false;
            }
        }

[上山老人]

似懂非懂 顶个先