为什么我的方法总是返回null

<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));
}

为什么总是返回null ?

我想查询局部性，但我的变量总是包含null。我最近写了一个类似的程序代码，可以工作，但现在有一个命名空间，不明白问题是什么。