Reading XML with a Namespace via XElement

Question

I'm working on an application that includes an RSS reader, and came across something I don't know how to handle.

The XML file is formed like so:

<?xml version="1.0" encoding="windows-1251"?>
<rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1/">
	<channel>
		<title>Feed Title</title>
		<link>http://feed.net/</link>
		<language>en</language>
		<description>A really cool feed</description>
		<generator>DataLife Engine</generator>
		<item>
			<title>Item Title</title>
			<guid isPermaLink="true">http://feed.net/item.html</guid>
			<link>http://feed.net/item.html</link>
			<description><![CDATA[<div align="center">a bunch of HTML in here</div><br /><br />]]></description>
			<category><![CDATA[Category Name]]></category>
			<dc:creator>Creator Name</dc:creator>
			<pubDate>Tue, 02 Mar 2010 17:34:33 +0300</pubDate>
		</item>
	</channel>
</rss>

The problem I have is this:

When I attempt to read the creator element with

NewItem.Creator = thisItem.Element("creator").Value;

I get an error, because thisItem.Element("creator") is null.  How can I correctly resolve this element?  I've tried

NewItem.Creator = thisItem.Element("dc:creator").Value;

but that gives me an error saying that ":" is not a valid character in an element name. 

I'm guessing I'll have to parse the namespace and prepend it to the element name, but how would I do that?

Thanks!

Gabe

Answer 1

Do you know the namespace when writing the code? Then you can simply do
XNamespace dc = "http://purl.org/dc/elements/1.1/";
in your code and then use e.g.
thisItem.Element(dc + "creator).Value

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MVP XML My blog

Answer 2

Yes, that will work if I always know the namespace, but I'm concerned that, since this will be reading RSS feeds "in the wild", that I might not always know the namespace beforehand.

Answer 3

Yes, that will work if I always know the namespace, but I'm concerned that, since this will be reading RSS feeds "in the wild", that I might not always know the namespace beforehand.

But how do you identify which element(s) you are interested in? A feed can have any kind of elements in any namespace, which ones are you looking for?

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MVP XML My blog

Answer 4

Hello Gabe,

 

 

How is the problem at your side?   If you need any further assistance, please feel free to let us know. 
 

Have a nice day!

 

 

Best Regards,
Lingzhi Sun

MSDN Subscriber Support in Forum

If you have any feedback on our support, please contact [e-mail]

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Answer 5

Hey guys, I'm struggling on this same issue in a Metro xaml + c# app. The sample documentation for rss works great, except when you're feed included dc:creator instead of authors.

Here's the code I've got so far based on the discussions above.

         foreach (SyndicationItem item in feed.Items)
                {
                    WriterItem WriterItem = new WriterItem();
                    WriterItem.Title = item.Title.Text;
                    WriterItem.PubDate = item.PublishedDate.DateTime;
                  
                    XNamespace dc = "http://purl.org/dc/elements/1.1/";
                    WriterItem.Author = item(dc + "creator").ToString;

                    //WriterItem.Author = item.Authors[0].Name.ToString();

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techAU http://techAU.tv

Answer 6

I think you are struggling with a different API, namely the SyndicationFeed/SyndicationItem API. I think the API is complex but poorly documented, I managed to fiddle together a sample nevertheless:

            SyndicationFeed feed;
            using (XmlReader xr = XmlReader.Create("../../XMLFile7.xml"))
            {
                feed = SyndicationFeed.Load(xr);
            }

            const string dcNs = "http://purl.org/dc/elements/1.1/";

            foreach (SyndicationItem item in feed.Items)
            {
                List<SyndicationElementExtension> elements =
                    item.ElementExtensions.Where(el => el.OuterNamespace == dcNs && el.OuterName == "creator").ToList();
                List<string> creators = new List<string>(elements.Count);
                
                foreach (SyndicationElementExtension element in elements)
                {
                    using (XmlReader xr = element.GetReader())
                    {
                        XElement xEl = XElement.ReadFrom(xr) as XElement;
                        creators.Add(xEl.Value);
                    }
                }
                Console.WriteLine("Item {0} has {1} creators: ", item.Title != null ? item.Title.Text : "", creators.Count);
                foreach (string creator in creators)
                {
                    Console.WriteLine("{0}", creator);
                }
                Console.WriteLine();
            }

There might be easier ways to read out such elements, unfortunately there is not much documentation on those classes.

---

MVP Data Platform Development My blog

Answer 7

Here is a simplification of the code, as far as the LINQ part is concerned:

            SyndicationFeed feed;
            using (XmlReader xr = XmlReader.Create("sheet.rss"))
            {
                feed = SyndicationFeed.Load(xr);
            }

            const string dcNs = "http://purl.org/dc/elements/1.1/";

            foreach (SyndicationItem item in feed.Items)
            {
                List<string> creators = 
                    item
                    .ElementExtensions
                    .Where(el => el.OuterNamespace == dcNs && el.OuterName == "creator")
                    .Select(el => (XElement.ReadFrom(el.GetReader()) as XElement).Value)
                    .ToList();
 
                Console.WriteLine("Item {0} has {1} creators: ", item.Title != null ? item.Title.Text : "", creators.Count);
                foreach (string creator in creators)
                {
                    Console.WriteLine("{0}", creator);
                }
                Console.WriteLine();
            }

---

MVP Data Platform Development My blog

Answer 8

Thanks, but hasn't helped. I agree the SyndicationItems is poorly documented for WinRT xaml c#. Will persist with searching on a solution.

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techAU http://techAU.tv

Answer 9

The code I posted works with .NET 4.0 but it seems the API is different with WinRT.

I currently have no way here to write/compile/test against WinRT so the following is meant purely as a suggestion based on the MSDN docs:

            foreach (SyndicationItem item in feed.Items)
            {
                List<string> creators = 
                    item
                    .ElementExtensions
                    .Where(el => el.NodeNamespace = "http://purl.org/dc/elements/1.1/" && el.NodeName == "creator")
                    .Select(el => el.NodeValue)
                    .ToList();
 
                Console.WriteLine("Item {0} has {1} creators: ", item.Title != null ? item.Title.Text : "", creators.Count);
                foreach (string creator in creators)
                {
                    Console.WriteLine("{0}", creator);
                }
                Console.WriteLine();
            }

---

MVP Data Platform Development My blog

Answer 10

Close, but there's no .where parameter in the ElementExtensions. Appreciate your help.

---

techAU http://techAU.tv

Answer 11

The Where and Select are LINQ query methods, if that is not supported then try a simple foreach loop along the lines of e.g.

            foreach (SyndicationItem item in feed.Items)
            {
                List<string> creators = new List<string>();
                foreach (var el in item.ElementExtensions)
                {
                   if (el.NodeNamespace == "http://purl.org/dc/elements/1.1/" && el.NodeName == "creator")
                   {
                      creators.Add(el.NodeValue);
                   } 
                }
 
                Console.WriteLine("Item {0} has {1} creators: ", item.Title != null ? item.Title.Text : "", creators.Count);
                foreach (string creator in creators)
                {
                    Console.WriteLine("{0}", creator);
                }
                Console.WriteLine();
            }

---

MVP Data Platform Development My blog

Answer 12

That was definitely helpful and my code now doesn't show any errors.. it does compile, but when I seen no author text, I started debugging and seen that after it hit the foreach line the rest was skipped passed. Any ideas? I think we're almost there.

foreach (SyndicationItem item in feed.Items)
                {
                    FeedItem feedItem = new FeedItem();
                    feedItem.Title = item.Title.Text;
                    feedItem.PubDate = item.PublishedDate.DateTime;

                    //Get Author from dc:creator field in RSS
                    List<string> creators = new List<string>();
                    foreach (var el in item.ElementExtensions)
                    {
                        if (el.NodeNamespace == "http://purl.org/dc/elements/1.1/" && el.NodeName == "creator")
                        {
                           creators.Add(el.NodeValue);
                        }
                    }
                    foreach (string creator in creators)
                    {
                        feedItem.Author = creator;
                    }

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techAU http://techAU.tv

Answer 13

Does the feed you want to read in declare the prefix "dc" for the namespace URI "http://purl.org/dc/elements/1.1/" used in the code sample? Or is a different URL declared there?

And what does the debugger show for

  item.ElementExtensions

are the any elements contained in that collection? What's it Count property?

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MVP Data Platform Development My blog

Answer 14

Hey Martin, yes the feed absolutely uses the ns URI is http://purl.org/dc/elements/1.1/

As for the return from item.ElementExtensions, it says the count is 6, but as I said passes right over it.

Happy to provide further info.

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techAU http://techAU.tv

Answer 15

As for the return from item.ElementExtensions, it says the count is 6, but as I said passes right over it.

Happy to provide further info.

I am not sure what to suggest, if the Count property shows 6 items then I don't understand why a foreach loop does not process them.

Does using an explicit type with e.g.

  foreach (ISyndicationNode el in item.ElementExtensions) { ... }

process the items in the collection?

It might be better to ask in a forum for Metro style app development with C#, hopefully other developers there are more successful on helping with the code than I am by trying to read the documentation.

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MVP Data Platform Development My blog