Finding element attribute with XDocument

Question

I'm trying to get the PurchaseDate from the following XML structure (a receipt from an in-app purchase in Windows Phone):

<Receipt Version="1.0" CertificateId="..." xmlns="http://schemas.microsoft.com/windows/2012/store/receipt">
  <ProductReceipt PurchasePrice="$0" PurchaseDate="2013-05-20T19:27:09.755Z" Id="..." AppId="..." ProductId="Unlock" ProductType="Consumable" PublisherUserId="..." PublisherDeviceId="..." MicrosoftProductId="..." />
  <Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
    <SignedInfo>
      <CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315" />
      <SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256" />
      <Reference URI="">
        <Transforms>
          <Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" />
        </Transforms>
        <DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256" />
        <DigestValue>...</DigestValue>
      </Reference>
    </SignedInfo>
    <SignatureValue>...</SignatureValue>
  </Signature>
</Receipt>

My code goes as follows:

XDocument doc = XDocument.Parse(receiptXml);

string date = doc.Root.Element("ProductReceipt").Attribute("PurchaseData").Value;

This keeps raising an access error, because doc.Root.Element("ProductReceipt") is null. Why is XDocument not getting the ProductReceipt element?

Answer 1

Just add namespace to your LINQ to XML query. Because you have default namespace declaration at the root node xmlns="http://schemas.microsoft.com/windows/2012/store/receipt" you also need to specify it in your query.

Next code shows an example:

XDocument doc = XDocument.Parse(receiptXml);

XNamespace xmlns = "http://schemas.microsoft.com/windows/2012/store/receipt";

string date = doc.Root
                 .Element(xmlns + "ProductReceipt")
                 .Attribute("PurchaseDate")
                 .Value;

Console.WriteLine(date);

prints:

2013-05-20T19:27:09.755Z

There is also a namespace agnostic approach:

string date = doc.Root
                 .Elements()
                 .First(node => node.Name.LocalName == "ProductReceipt")
                 .Attribute("PurchaseDate")
                 .Value;