为什么我的方法总是返回 null？

Question

<Response xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
          xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
          xmlns="http://schemas.microsoft.com/search/local/ws/rest/v1">
  <Copyright>Copyright &#xA9; 2011 Microsoft and its suppliers. All rights
   reserved. This API cannot be accessed and the content and any results
   may not be used, reproduced or transmitted in any manner without express
   written permission from Microsoft Corporation.</Copyright>
  <BrandLogoUri>[http://dev.virtualearth.net/Branding/logo_powered_by.png]</BrandLogoUri>
  <StatusCode>200</StatusCode>
  <StatusDescription>OK</StatusDescription>
  <AuthenticationResultCode>ValidCredentials</AuthenticationResultCode>
  <TraceId>50230e70257e4ed5a5002a3d4a625c83|LTSM001156|02.00.159.1700|LTSMSNVM001471, LTSMSNVM001477</TraceId>
  <ResourceSets>
    <ResourceSet>
      <EstimatedTotal>1</EstimatedTotal>
      <Resources>
        <Location>
          <Name>1 Microsoft Way, Redmond, WA 98052</Name>
          <Point>
            <Latitude>47.640568390488625</Latitude>
            <Longitude>-122.1293731033802</Longitude>
          </Point>
          <BoundingBox>
            <SouthLatitude>47.636705672917948</SouthLatitude>
            <WestLongitude>-122.137016420622</WestLongitude>
            <NorthLatitude>47.6444311080593</NorthLatitude>
            <EastLongitude>-122.1217297861384</EastLongitude>
          </BoundingBox>
          <EntityType>Address</EntityType>
          <Address>
            <AddressLine>1 Microsoft Way</AddressLine>
            <AdminDistrict>WA</AdminDistrict>
            <AdminDistrict2>King Co.</AdminDistrict2>
            <CountryRegion>United States</CountryRegion>
            <FormattedAddress>1 Microsoft Way, Redmond, WA 98052</FormattedAddress>
            <Locality>Redmond</Locality>
            <PostalCode>98052</PostalCode>
          </Address>
          <Confidence>Medium</Confidence>
        </Location>
      </Resources>
    </ResourceSet>
  </ResourceSets>
</Response>

我的查询以前看起来像：

private void getData()
{
    // Api letőltése
    WebClient webClient = new WebClient();

    string url = "http://dev.virtualearth.net/REST/v1/Locations/" 
                 + _location + "?o=xml&key=App-asdf";

    webClient.DownloadStringCompleted += (s, e) =>
        {
            if (e.Error != null)
                return;

            XDocument xmlLocation = XDocument.Parse(e.Result);

            var ns = XNamespace.Get("http://schemas.microsoft.com/search/local/ws/rest/v1");
            var locality = from q in xmlLocation.Descendants(ns + "Address")
                           select (string)q.Element(ns + "Locality").Value;
        };

    webClient.DownloadStringAsync(new Uri(url));
}

为什么它总是返回 null？

我想查询位置，但我的变量始终包含 null。我最近编写了一个类似的程序代码，该代码可以工作，但现在有一个名称空间，并且不明白问题是什么。

Answer 1

我刚刚针对列出的 XML 运行了您的查询，它生成了“Redmond”。

所以：把它分解。您遇到通信或线程问题。

    if (e.Error != null)
                return;

这是掩盖问题的好方法。

Answer 2

var locality = xmlLocation.Descendants(ns + "Locality").Select( x => x.Value);