创建XML

//创建XML
XElement xelement = new XElement("request",
                  new XElement("head",
                  new XElement("msgId", System.Guid.NewGuid().ToString()),//
                  new XElement("timeStamp", string.Format("{0:yyyyMMddHHmmssfffff}", DateTime.Now)),
                  new XElement("session", ""),
                  new XElement("userCode", "")),//

              new XElement("body",
                  new XElement("vehicle",
                          new XElement("brandName", brandName))));//车型名称
            string RequestCarsXML = string.Format("<?xml version="1.0" encoding="UTF-8"?>{0}{1}", System.Environment.NewLine, xelement.ToString());