如何选择XDocument中的项目？

Question

在下面的XML中，我试图检索所有trkpt项目，以便我可以使用lat/lon属性值执行任务。我认为LINQ到XML将是最简单的方法，但我无法得到任何结果在foreach循环中返回。我究竟做错了什么？

此代码是在一个控制台应用程序的Main（）方法：

var filename = @"C:\temp\sample_output.gpx"; 

var xDoc = XDocument.Load(filename); 

XNamespace xmlns = "http://www.topografix.com/GPX/1/1"; 
XNamespace gpxtpx = "http://www.garmin.com/xmlschemas/TrackPointExtension/v1"; 
XNamespace wptx1 = "http://www.garmin.com/xmlschemas/WaypointExtension/v1"; 
XNamespace gpxx = "http://www.garmin.com/xmlschemas/GpxExtensions/v3"; 
XNamespace gpxtrkx = "http://www.garmin.com/xmlschemas/TrackStatsExtension/v1"; 

foreach (var item in xDoc.Descendants(gpxtpx + "trkpt")) 
{ 
    Console.WriteLine(item.Element(gpxtpx + "trkpt").Value); 
} 

Console.Read(); 

XML数据我试图与上面的代码来处理。纬度/经度值被修改。

<?xml version="1.0" encoding="UTF-8" standalone="no" ?> 
    <gpx xmlns="http://www.topografix.com/GPX/1/1" 
xmlns:gpxx="http://www.garmin.com/xmlschemas/GpxExtensions/v3" 
xmlns:gpxtrkx="http://www.garmin.com/xmlschemas/TrackStatsExtension/v1" 
xmlns:wptx1="http://www.garmin.com/xmlschemas/WaypointExtension/v1" 
xmlns:gpxtpx="http://www.garmin.com/xmlschemas/TrackPointExtension/v1" 
creator="Oregon 600" version="1.1" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:schemaLocation="http://www.topografix.com/GPX/1/1 
http://www.topografix.com/GPX/1/1/gpx.xsd 
http://www.garmin.com/xmlschemas/GpxExtensions/v3 
http://www8.garmin.com/xmlschemas/GpxExtensionsv3.xsd 
http://www.garmin.com/xmlschemas/TrackStatsExtension/v1 
http://www8.garmin.com/xmlschemas/TrackStatsExtension.xsd 
http://www.garmin.com/xmlschemas/WaypointExtension/v1 
http://www8.garmin.com/xmlschemas/WaypointExtensionv1.xsd 
http://www.garmin.com/xmlschemas/TrackPointExtension/v1 
http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd"> 
     <metadata> 
      <link href="http://www.garmin.com"> 
       <text>Garmin International</text> 
      </link> 
      <time>2016-04-18T01:19:07Z</time> 
     </metadata> 
     <trk> 
      <name>2016-04-17 20:19:01</name> 
      <extensions> 
       <gpxx:TrackExtension> 
        <gpxx:DisplayColor>Magenta</gpxx:DisplayColor> 
       </gpxx:TrackExtension> 
      </extensions> 
      <trkseg> 
       <trkpt lat="44.123" lon="-89.123"> 
        <ele>343.61</ele> 
        <time>2016-04-17T22:53:34Z</time> 
       </trkpt> 
       <trkpt lat="44.123" lon="-89.123"> 
        <ele>343.58</ele> 
        <time>2016-04-17T22:53:35Z</time> 
       </trkpt> 
       <trkpt lat="44.123" lon="-89.123"> 
        <ele>343.56</ele> 
        <time>2016-04-17T22:53:36Z</time> 
       </trkpt> 
       <trkpt lat="44.123" lon="-89.123"> 
        <ele>343.55</ele> 
        <time>2016-04-17T22:53:37Z</time> 
       </trkpt> 
       <trkpt lat="44.123" lon="-89.123"> 
        <ele>343.62</ele> 
        <time>2016-04-17T22:53:38Z</time> 
       </trkpt> 
      </trkseg> 
     </trk> 
    </gpx> 

Answer 1

您正在使用错误的命名空间。元素（包括trkpt）的默认命名空间是http://www.topografix.com/GPX/1/1，由于这样的：

xmlns="http://www.topografix.com/GPX/1/1" 

我强烈建议你改变你的变量名gpxNs以表明它的价值，然后使用它：

XNamespace gpxNs = "http://www.topografix.com/GPX/1/1"; 
... 
foreach (var item in xDoc.Descendants(gpxNs + "trkpt")) 

Answer 2

您可以使用XML Linq

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Xml; 
using System.Xml.Linq; 

namespace ConsoleApplication1 
{ 
    class Program 
    { 
     const string FILENAME = @"c:\temp\test.xml"; 
     static void Main(string[] args) 
     { 
      XDocument doc = XDocument.Load(FILENAME); 

      XElement trkseg = doc.Descendants().Where(x => x.Name.LocalName == "trkseg").FirstOrDefault(); 
      XNamespace ns = trkseg.Name.Namespace; 

      var l_l = trkseg.Elements(ns + "trkpt").Select(x => new 
      { 
       lat = x.Attribute("lat").Value, 
       lon = x.Attribute("lon").Value 
      }).ToList(); 

     } 
    } 
}