webservice服务输出xml格式自定义格式内容

  [WebMethod(Description = "获取对应产品Id及Name,Productlist是以,分割的productid字符串")]
        public string GetProductListByIds(string Productlist)
        {
           ProductMng productMng = new ProductMng(connString);

            System.IO.MemoryStream productlist = new System.IO.MemoryStream();

            XmlTextWriter writer = new XmlTextWriter(productlist, System.Text.Encoding.UTF8);
            writer.WriteStartDocument();
            writer.WriteStartElement("productlist");

            string[] ids = Productlist.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
            foreach (string id in ids)
            {
                Model.Product product = productMng.GetItem(int.Parse(id));
                writer.WriteStartElement("product");
                writer.WriteElementString("ID", product.ID.ToString());
                writer.WriteElementString("Name", product.Name);
                writer.WriteElementString("NameEn", product.NameEn);
                writer.WriteEndElement();
            }

            writer.WriteEndElement();
            writer.WriteEndDocument();
            writer.Flush();
            writer.Close();

            return System.Text.Encoding.UTF8.GetString(productlist.ToArray());
        }