急！.net查询短信群发剩余条数

接口请求XML包格式：
<?xml version='1.0' encoding='UTF-8'?>
  <reqinfo>
    <user_key>7Ww6VqPhUHI=</user_key>
  </reqinfo>

.net不知道怎么使用XML --------------------编程问答-------------------- 使用XMLDocument来解析xml，增删改 --------------------编程问答-------------------- 能给我一个例子吗没用过XML 不知道什么写 --------------------编程问答--------------------             XmlDocument xml = new XmlDocument();
            xml.Load("XML地址");
            XmlNode node =  xml.SelectSingleNode("/reqinfo/user_key");
            string test = node.InnerText;
--------------------编程问答--------------------

引用 3 楼的回复:

            XmlDocument xml = new XmlDocument();
            xml.Load("XML地址");
            XmlNode node =  xml.SelectSingleNode("/reqinfo/user_key");
            string test = node.InnerText;

public string GetHtmlFromUrl(string url)
    {
        string strRet =null;
        if (url == null || url.Trim().ToString() == "")
        {
            return strRet;
        }
        string targeturl = url.Trim().ToString();
        try
        {
            HttpWebRequest hr = (HttpWebRequest)WebRequest.Create(targeturl);
            hr.UserAgent = test;// "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)";
            hr.Method = "GET";
            hr.Timeout = 30 * 60 * 1000;
            WebResponse hs = hr.GetResponse();
            Stream sr = hs.GetResponseStream();
            StreamReader ser = new StreamReader(sr, Encoding.Default);
            strRet = ser.ReadToEnd();
        }
        catch (Exception ex)
        {
            strRet = null;
        }
        return strRet;
    }
要把test 传给GetHtmlFromUrl（）中的哪里？ --------------------编程问答-------------------- GetHtmlFromUrl()方法是用于去抓网上的xml文档？你可以先写到本地。
using (System.IO.FileStream fs = System.IO.File.Create(targeturl))
        {
            byte[] info = new UTF8Encoding(true).GetBytes(strRet);
            fs.Write(info, 0, info.Length);
        }
XmlDocument xml = new XmlDocument();
  xml.Load(targeturl);
  XmlNode node = xml.SelectSingleNode("/reqinfo/user_key");
  string test = node.InnerText;
test即为7Ww6VqPhUHI=

补充：.NET技术 ,  ASP.NET