创建XML

                XmlDocument doc = doc = new XmlDocument();
                XmlDeclaration dec = dec = doc.CreateXmlDeclaration("1.0", "GB2312", null);
                doc.AppendChild(dec);
                //创建节点（一级）
                XmlElement root = doc.CreateElement("Customers");
                doc.AppendChild(root);
                XmlNode node = null;
                XmlElement element1 = null;
                XmlWriterSettings setting = new XmlWriterSettings();
                XmlWriter writer = null;

                //XmlWriterSettings setting = new XmlWriterSettings();
                //setting.Indent = true;
                //setting.Encoding = System.Text.Encoding.GetEncoding("gb2312");//设置编码格式。
                //using (XmlWriter writer = XmlWriter.Create(Server.MapPath("~/XML/XMLFile2.xml"), setting))
                //{
                //    ds.WriteXml(writer, XmlWriteMode.IgnoreSchema);
                //}
                for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
                {
                    //创建节点（二级）
                    node = doc.CreateElement("Customer");
                    //创建节点（三级）
                    element1 = doc.CreateElement("CNo");
                    element1.InnerText = ds.Tables[0].Rows[i]["Num"].ToString();
                    node.AppendChild(element1);

                    root.AppendChild(node);

                    setting.Indent = true;
                    setting.Encoding = System.Text.Encoding.GetEncoding("gb2312");//设置编码格式。
                    using (writer = XmlWriter.Create(Server.MapPath("~/CustmerXML/CustmerFile.xml"), setting))
                    {
                        doc.Save(writer);
                    }
                }
                result = "操作成功";