enum 不能从string 转换?

public void LoadPara()
        {            RegistryKey rk = Registry.LocalMachine;            RegistryKey hklm = rk.CreateSubKey(RegRoot + ID.ToString());
            commPort.PortName = (string)(hklm.GetValue("PortName","COM1"));            commPort.BaudRate = (int)(hklm.GetValue("BaudRate", 9600));            commPort.Parity = (Parity)(hklm.GetValue("Parity",Parity.None));            commPort.StopBits = (StopBits)(hklm.GetValue("StopBits", StopBits.One));            hklm.Close();        }