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Linq to XML，用XNameSpace解析

分类: 技术问答 • 2022-07-22 23:38:31
问题描述：

我正在从这个天气链接“http://alerts.weather.gov/cap/us.php?x=0”解析这个XML。我发现了一个很好的示例代码，它非常适合解析'tile'和'cap：event'，但我需要解析'cap：geocode'并获取其下的（'value'&'valueName'）元素列表。Linq to XML，用XNameSpace解析

<entry> 
    ... 
    <cap:geocode> 
<valueName>FIPS6</valueName> 
<value>002016</value> 
<valueName>UGC</valueName> 
<value>AKZ185</value> 
</cap:geocode> 
    ... 
</entry>

这里是我使用的代码：

XDocument doc = XDocument.Parse(objText); 
XNamespace ns = XNamespace.Get("http://www.w3.org/2005/Atom"); 
XNamespace nsCap = XNamespace.Get("urn:oasis:names:tc:emergency:cap:1.1"); 
var xlist = doc.Descendants(ns + "entry").Select(elem => new 
{ 
    Title = elem.Descendants(ns + "title").FirstOrDefault(), 
    AreaDesc = elem.Descendants(nsCap + "areaDesc").FirstOrDefault(), 
    Geocode = elem.Descendants(nsCap + "geocode").Select(gc => new 
    { 
     val = gc.Element("value"), 
     valName = gc.Element("valueName") 
    }).ToList() 
}); 

foreach (var el in xlist) 
{ 
    System.Diagnostics.Debug.WriteLine(string.Format("title: {0}, AreaDesc: {1}", 
     el.Title != null ? el.Title.Value : string.Empty, 
     el.AreaDesc != null ? el.AreaDesc.Value : string.Empty)); 
    foreach (var x in el.Geocode) 
    { 
     string value = x.val.Value; 
     string valueName = x.valName.Value; 
    } 
}

当我运行的代码中，el.Geocode元素包含空值。我不知道为什么它不给我价值。

这里是weather.gov的XML：

 <?xml version = '1.0' encoding = 'UTF-8' standalone = 'yes'?> 

    <!-- 
    This atom/xml feed is an index to active advisories, watches and warnings 
    issued by the National Weather Service. This index file is not the complete 
    Common Alerting Protocol (CAP) alert message. To obtain the complete CAP 
    alert, please follow the links for each entry in this index. Also note the 
    CAP message uses a style sheet to convey the information in a human readable 
    format. Please view the source of the CAP message to see the complete data 
    set. Not all information in the CAP message is contained in this index of 
    active alerts. 
    --> 


    <feed 
    xmlns = 'http://www.w3.org/2005/Atom' 
    xmlns:cap = 'urn:oasis:names:tc:emergency:cap:1.1' 
    xmlns:ha = 'http://www.alerting.net/namespace/index_1.0' 
    > 
    <!-- http-date = Thu, 13 Feb 2014 07:35:00 GMT --> 

    <id>http://alerts.weather.gov/cap/us.atom</id> 
    <logo>http://alerts.weather.gov/images/xml_logo.gif</logo> 
    <generator>NWS CAP Server</generator> 
    <updated>2014-02-13T14:35:00-05:00</updated> 
    <author> 
    <name>[email protected]</name> 
    </author> 
    <title>Current Watches, Warnings and Advisories for the United States Issued by the National Weather Service</title> 
    <link href='http://alerts.weather.gov/cap/us.atom'/> 

     <entry> 
     <id>http://alerts.weather.gov/cap/wwacapget.php?x=AK12514240A72C.BlizzardWarning.1251424FD8A0AK.AFCWSWALU.51c52d9702226c0667b44fead05cc33e</id> 
     <updated>2014-02-13T09:43:00-09:00</updated> 
     <published>2014-02-13T09:43:00-09:00</published> 
     <author> 
     <name>[email protected]</name> 
     </author> 
     <title>Blizzard Warning issued February 13 at 9:43AM AKST until February 14 at 9:00AM AKST by NWS</title> 
     <link href='http://alerts.weather.gov/cap/wwacapget.php?x=AK12514240A72C.BlizzardWarning.1251424FD8A0AK.AFCWSWALU.51c52d9702226c0667b44fead05cc33e'/> 
     <summary>...ARCTIC AIR RETURNING TO SOUTHWEST ALASKA... .VERY COLD AIR ACCOMPANIED BY BRISK NORTHERLY WINDS WILL MAKE FOR DANGEROUS WIND CHILLS ACROSS MUCH OF SOUTHWEST ALASKA THROUGH FRIDAY. THESE WIND CHILL VALUES WILL BE SOME OF THE COLDEST OF THE ENTIRE WINTER THUS FAR. STRENGTHENING WINDS WILL CONTINUE TO SURGE SOUTHWARD ALONG THE ALASKA PENINSULA AND EASTERN ALEUTIANS.</summary> 
     <cap:event>Blizzard Warning</cap:event> 
     <cap:effective>2014-02-13T09:43:00-09:00</cap:effective> 
     <cap:expires>2014-02-14T09:00:00-09:00</cap:expires> 
     <cap:status>Actual</cap:status> 
     <cap:msgType>Alert</cap:msgType> 
     <cap:category>Met</cap:category> 
     <cap:urgency>Expected</cap:urgency> 
     <cap:severity>Severe</cap:severity> 
     <cap:certainty>Likely</cap:certainty> 
     <cap:areaDesc>Eastern Aleutians</cap:areaDesc> 
     <cap:polygon></cap:polygon> 
     <cap:geocode> 
     <valueName>FIPS6</valueName> 
     <value>002016</value> 
     <valueName>UGC</valueName> 
     <value>AKZ185</value> 
     </cap:geocode> 
     <cap:parameter> 
     <valueName>VTEC</valueName> 
     <value>/X.UPG.PAFC.WW.Y.0009.140213T2300Z-140214T1800Z/ 
    /X.EXB.PAFC.BZ.W.0007.140213T1843Z-140214T1800Z/</value> 
     </cap:parameter> 
     </entry> 

     <entry> 
     <id>http://alerts.weather.gov/cap/wwacapget.php?x=AK12514240A72C.BlizzardWarning.125142504DD0AK.AFCWSWALU.b6bd8b4269647f8f24176412e2248b93</id> 
     <updated>2014-02-13T09:43:00-09:00</updated> 
     <published>2014-02-13T09:43:00-09:00</published> 
     <author> 
     <name>[email protected]</name> 
     </author> 
     <title>Blizzard Warning issued February 13 at 9:43AM AKST until February 14 at 12:00PM AKST by NWS</title> 
     <link href='http://alerts.weather.gov/cap/wwacapget.php?x=AK12514240A72C.BlizzardWarning.125142504DD0AK.AFCWSWALU.b6bd8b4269647f8f24176412e2248b93'/> 
     <summary>...ARCTIC AIR RETURNING TO SOUTHWEST ALASKA... .VERY COLD AIR ACCOMPANIED BY BRISK NORTHERLY WINDS WILL MAKE FOR DANGEROUS WIND CHILLS ACROSS MUCH OF SOUTHWEST ALASKA THROUGH FRIDAY. THESE WIND CHILL VALUES WILL BE SOME OF THE COLDEST OF THE ENTIRE WINTER THUS FAR. STRENGTHENING WINDS WILL CONTINUE TO SURGE SOUTHWARD ALONG THE ALASKA PENINSULA AND EASTERN ALEUTIANS.</summary> 
     <cap:event>Blizzard Warning</cap:event> 
     <cap:effective>2014-02-13T09:43:00-09:00</cap:effective> 
     <cap:expires>2014-02-14T12:00:00-09:00</cap:expires> 
     <cap:status>Actual</cap:status> 
     <cap:msgType>Alert</cap:msgType> 
     <cap:category>Met</cap:category> 
     <cap:urgency>Expected</cap:urgency> 
     <cap:severity>Severe</cap:severity> 
     <cap:certainty>Likely</cap:certainty> 
     <cap:areaDesc>Alaska Peninsula</cap:areaDesc> 
     <cap:polygon></cap:polygon> 
     <cap:geocode> 
     <valueName>FIPS6</valueName> 
     <value>002013 002164</value> 
     <valueName>UGC</valueName> 
     <value>AKZ181</value> 
     </cap:geocode> 
     <cap:parameter> 
     <valueName>VTEC</valueName> 
     <value>/X.EXT.PAFC.BZ.W.0007.140213T1843Z-140214T2100Z/</value> 
     </cap:parameter> 
     </entry> 
</entry> 

</feed>

答

我想你的第一个问题是，你缺少的命名空间中的代码，这部分

val = gc.Element("value"), 
valName = gc.Element("valueName")

我认为你的第二个问题是您已将匿名类型的GeoCode属性写为<cap:geocode>元素的列表，而您期望将其用作<cap:geocode>元素中valueName/value对的列表。至少这是我的假设。因此，这可能是更接近你想要什么

var xlist = doc.Descendants(ns + "entry").Select(elem => new 
{ 
    Title = elem.Descendants(ns + "title").FirstOrDefault(), 
    AreaDesc = elem.Descendants(nsCap + "areaDesc").FirstOrDefault(), 
    GeocodeElements = elem.Descendants(nsCap + "geocode").Descendants() 
}); 

foreach (var el in xlist) 
{ 
    System.Diagnostics.Debug.WriteLine(string.Format("title: {0}, AreaDesc: {1}", 
     el.Title != null ? el.Title.Value : string.Empty, 
     el.AreaDesc != null ? el.AreaDesc.Value : string.Empty)); 
    var geoCodeValues = el.GeocodeElements 
       .Where(o => o.Name == ns + "value").ToList(); 
    var geoCodeValueNames = el.GeocodeElements 
       .Where(o => o.Name == ns + "valueName").ToList(); 
    var pairs = geoCodeValueNames.Zip(geoCodeValues, (vn, v) => 
         new Tuple<String, String>(vn.Value, v.Value)).ToList(); 
}

注意，在最后一行我用元组，而不是匿名类型，因为它不会让我创建一个匿名类型有两个属性都命名为“价值” 。我期望这只是一个开始（我不确定我的代码是多么健壮 - 比如，如果不是每个值都与valueName匹配，等等），并且可能有其他方法来解决这个问题。我只是想让你更接近我认为你想要做的事情。

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