asp.net 循环添加xml节点,该怎么处理

asp.net 循环添加xml节点
功能是为了实现调用快递接口，对快递运单的批量查询

功能初始页面

输入数据后


现在遇到的问题就是怎么动态添加xml节点，想实现的结果是

XML code

 <BatchQueryRequest>  <logisticProviderID>xxx</logisticProviderID>   <clientID>xxx</clientID>   <orders>     <order>        <mailNo>1111111111</mailNo>    </order>    <order>        <mailNo>2222222222</mailNo>    </order>   </orders>  </BatchQueryRequest>

C# code

            string orderNo = this.IndexwaybillNo.Value.Trim();            string clientId = "xxx";             string logisticProviderID = "xxx";             string[] rs = orderNo.Trim().Split('/');            string xml = "<BatchQueryRequest>" +                      "<logisticProviderID>" + logisticProviderID + "</logisticProviderID>" +                      "<clientID>" + clientId + "</clientID>" +                      "<orders>" +                      "</orders>" +                  "</BatchQueryRequest>";            XmlDocument xmlDoc = new XmlDocument();            xmlDoc.LoadXml(xml);            XmlNode xmlNode = xmlDoc.SelectSingleNode("BatchQueryRequest/orders");                     foreach (string s in rs)            {                if (s.Trim().Length!= 10)                {                    this.lblTime.Text = "";                    Common.Alert("运单号输入不正确,请输入10位正确运单号");                                  }                else if (!op.StrIsInt(s))                {                    this.lblTime.Text = "";                    Common.Alert("运单号格式不正确,请输入10位正确运单号");                 }                else                {                    orderNo = s;                                       if (xmlNode != null)                    {                        XmlElement newElement = xmlDoc.CreateElement("order");//添加order节点                        XmlElement etitle = xmlDoc.CreateElement("mailNo"); //添加mailNo节点                        etitle.InnerXml = orderNo;                        newElement.AppendChild(etitle);                                              xmlNode.AppendChild(newElement);                    }                    xmlDoc.LoadXml(xml);                }                            }