使用XDocument.Load加载XML的后代

Question

I am attempting to use XDocument.Load to access some latitude and longitude figures. Here is the example XML document;

<?xml version="1.0" encoding="utf-8"?>
<Response xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/search/local/ws/rest/v1">
  <Copyright>Copyright © 2016 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>31a206847f9341d28689e0e7185e163d|DB40051719|7.7.0.0|DB4SCH010061262</TraceId>
  <ResourceSets>
    <ResourceSet>
      <EstimatedTotal>1</EstimatedTotal>
      <Resources>
        <Location>
          <Name>SW1A 1AA, London, London, United Kingdom</Name>
          <Point>
            <Latitude>51.501018524169922</Latitude>
            <Longitude>-0.14159967005252838</Longitude>
          </Point>
          <BoundingBox>
            <SouthLatitude>51.497155806599245</SouthLatitude>
            <WestLongitude>-0.14987251765942367</WestLongitude>
            <NorthLatitude>51.5048812417406</NorthLatitude>
            <EastLongitude>-0.1333268224456331</EastLongitude>
          </BoundingBox>
          <EntityType>Postcode1</EntityType>
          <Address>
            <AdminDistrict>England</AdminDistrict>
            <AdminDistrict2>London</AdminDistrict2>
            <CountryRegion>United Kingdom</CountryRegion>
            <FormattedAddress>SW1A 1AA, London, London, United Kingdom</FormattedAddress>
            <Locality>London</Locality>
            <PostalCode>SW1A 1AA</PostalCode>
          </Address>
          <Confidence>High</Confidence>
          <MatchCode>Good</MatchCode>
          <GeocodePoint>
            <Latitude>51.501018524169922</Latitude>
            <Longitude>-0.14159967005252838</Longitude>
            <CalculationMethod>Rooftop</CalculationMethod>
            <UsageType>Display</UsageType>
          </GeocodePoint>
        </Location>
      </Resources>
    </ResourceSet>
  </ResourceSets>
</Response>

And here is the code I am using attempting to access latitude and longitude;

    string latitude = XDocument.Load(@"test.xml").Root
                                            .Descendants("ResourceSets")
                                            .Descendants("ResourceSet")
                                            .Descendants("Resources")
                                            .Descendants("Location")
                                            .Descendants("GeocodePoint")
                                            .Select(element => element.Attribute("Latitude").Value).FirstOrDefault();

But this returns an empty string. How can I navigate the document correctly?

Answer 1

First thing you don't need to call in multiples level Descendants method if you want to get all GeocodePoint nodes. You can only do this:

XNamespace ns =  "http://schemas.microsoft.com/search/local/ws/rest/v1";
string latitude = XDocument.Load(@"test.xml")
                  .Descendants(ns+"GeocodePoint")
                  .Select(e=> (string)e.Element(ns+"Latitude"))
                  .FirstOrDefault();

With that call Linq to XML will retrieve all the GeocodePoints in your xml

If you want to get lat and long values, then you can project either to an anonymous type or a custom class (DTO) like this:

XNamespace ns =  "http://schemas.microsoft.com/search/local/ws/rest/v1";

var coord= XDocument.Load(@"xml.xml")
          .Descendants(ns+"GeocodePoint").Select(e => new { Lat = (string)e.Element(ns+"Latitude"), Lng = (string)e.Element(ns+"Longitude") })
          .FirstOrDefault();

About your issue

Your problem was you were calling Attribute method to get the Latitude value, but as you can see in your xml structure GeocodePoint node doesn't have that as an attribute, it is a nested element. That's way you need to use Element method instead. The second issue was you need to take the namespace into account as I show above.

Answer 2

You are not using namespace. Your Xml provided with namespace

<Response xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xmlns="http://schemas.microsoft.com/search/local/ws/rest/v1">

So you need to use it when searching for elements.

XDocument doc = XDocument.Load(@"C:\tmp\data.xml");

XNamespace ns = doc.Root.Name.Namespace;
string value = doc.Root.Descendants(ns + "Latitude").FirstOrDefault().Value; 

Or search without namespace, by LocalName of element

string value = doc.Root
                  .Descendants
                  .Where(element => element.Name.LocalName.Equals("Latitude"))
                  .FirstOrDefault()
                  .Value;

If you using Descendats method, then you can search straight for element you need.