获取XML里指定的节点内容信息

     HttpContent bw = new StringContent(StrXml, Encoding.UTF8, "application/Xml");
                 var Msg = await _httpClientFactory.CreateClient().PostAsync("http://xxxxx/api/kpbusiness", bw);
                 var ss = Msg.Content.ReadAsStringAsync();
                 StringReader Reader = new StringReader(ss.Result);
                 XmlDocument xmlDoc = new XmlDocument();
                 xmlDoc.Load(Reader);
                 XmlNodeList topM = xmlDoc.SelectNodes("//business");
                 string returncode;
                 string returnmsg;
                 string retappid;
                 string retid;
                 foreach (XmlElement element in topM)
                 {
                      returncode = element.GetElementsByTagName("returncode")[].InnerText;
                      returnmsg = element.GetElementsByTagName("returnmsg")[].InnerText;
                      retappid = element.GetElementsByTagName("returncode")[].InnerText;
                      retid = element.GetElementsByTagName("returncode")[].InnerText;
                 }