c# .net 将List序列化

/// <summary>

        /// 序列化List

        /// </summary>

        /// <param name="al"></param>

        /// <returns>string</returns>

        public string SerializeArrayList(ArrayList al)

        {

            Type[] extra = new Type[1];

            extra[0] = typeof(LocalNetInfo);

           // extra[0] = typeof(string);

            XmlSerializer xs = new XmlSerializer(typeof(ArrayList), extra);

            MemoryStream ms = new MemoryStream();

            XmlTextWriter tw = new XmlTextWriter(ms, Encoding.Default);

            xs.Serialize(tw, al);

            tw.Close();

            return Encoding.Default.GetString(ms.ToArray());

        }