如何在XML中选择单个节点？

Question

我正在尝试检索XML文档中单个节点的值。

以下是我尝试过的一些不起作用的方法：

public class Location
{
    private String latitude;

    public void updateLocation(String woeid)
    {
        String query = String.Format("http://weather.yahooapis.com/forecastrss?w={0}", woeid);

        XmlDocument weatherData = new XmlDocument();
        weatherData.Load(query);

        XmlNode channel = weatherData.SelectSingleNode("rss").SelectSingleNode("channel");
        XmlNamespaceManager man = new XmlNamespaceManager(weatherData.NameTable);
        man.AddNamespace("geo:lat", "http://xml.weather.yahoo.com/ns/rss/1.0");
        latitude = channel.SelectSingleNode("geo:lat", man).InnerText;

    }

这种方法也不起作用：

public class Location
{
    private String latitude;

    public void updateLocation(String woeid)
    {
        String query = String.Format("http://weather.yahooapis.com/forecastrss?w={0}", woeid);

        XmlDocument weatherData = new XmlDocument();
        weatherData.Load(query);

        XmlNode channel = weatherData.SelectSingleNode("rss").SelectSingleNode("channel");
        latitude = channel.SelectSingleNode("item").SelectSingleNode("geo:lat").InnerText;

    }

}

为什么我无法获得＆＃34; geo：lat＆＃34;的价值？

Answer 1

1）加载方法不会等待，因此它没有任何内容。请参阅HTTPGetXML（）函数以获取XML。

2）查看我如何创建命名空间并使用它。

3）使用// yweather：location。

向右跳到所需的节点

祝你好运

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Xml;
using System.Net;
using System.IO;

namespace mblog {
    public partial class WebForm1 : System.Web.UI.Page {

        public XmlDocument HTTPGetXML(string strURL) {
            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(strURL);
            req.Method = "GET";
            req.Timeout = 120000;  // 2 minutes

            XmlDocument xmlReturn = new XmlDocument();
            // UGH! not set by default!
            req.Proxy.Credentials = System.Net.CredentialCache.DefaultCredentials;

            // Set AllowWriteStreamBuffering to 'false'. 
            req.AllowWriteStreamBuffering = false;
            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
            string msg;

            try {
                // Get the response from the server
                StreamReader reader = new StreamReader(resp.GetResponseStream());
                msg = reader.ReadToEnd();
                xmlReturn.LoadXml(msg);
            } catch (Exception e) {
                throw new Exception("Error posting to server.", e);
            }
            return xmlReturn;
        }  

        protected void Page_Load(object sender, EventArgs e) {
            try {
                XmlDocument xmlWeather = HTTPGetXML("http://weather.yahooapis.com/forecastrss?w=2475688");

                NameTable nt = new NameTable();
                XmlNamespaceManager nsmgr;

                nsmgr = new XmlNamespaceManager(nt);
                nsmgr.AddNamespace("yweather", "http://xml.weather.yahoo.com/ns/rss/1.0");


                XmlNode ndLocation = xmlWeather.SelectSingleNode("//yweather:location", nsmgr);
                if( ndLocation != null ) {
                    string strCity = ndLocation.Attributes["city"].Value;
                }


            } catch (Exception ex) {
                Response.Write( ex.Message );
            }


        }
    }
}

Answer 2

事实证明我使用了错误的命名空间uri。 XML文档有两个名称空间，一个用于yweather，另一个用于geo。

您将在XML文档的顶部找到要使用的命名空间的正确uri。

此代码可让我成功检索geo:lat：

的值

public void updateLocation(String woeid)
        {
            String query = String.Format("http://weather.yahooapis.com/forecastrss?w={0}", woeid);

            XmlDocument weatherData = new XmlDocument();

            weatherData.Load(query);

            XmlNode channel = weatherData.SelectSingleNode("rss").SelectSingleNode("channel");
            XmlNamespaceManager man = new XmlNamespaceManager(weatherData.NameTable);
            man.AddNamespace("geo", "http://www.w3.org/2003/01/geo/wgs84_pos#");

            latitude = channel.SelectSingleNode("item").SelectSingleNode("geo:lat", man).InnerText;

        }