Parsing through XML elements in XmlReader

Question

I'm building an application that needs to run through an XML feed but I'm having a little trouble with getting certain elements.

I'm using the Twitter feed and want to run through all the <item> elements. I can connect fine and get the content from the feed but I can't figure out how to select only the item elements when I'm loopuing through reader.Read();.

Thanks for your help!

Is there a reason you have choosen an XmlReader over just loading the XML into a Document? What framework version? — AnthonyWJones
– AnthonyWJones, Commented Oct 28, 2008 at 12:32

Vinko Vrsalovic · Accepted Answer · 2008-10-28 12:54:01Z

The easiest way to do that is to use XPath. Example to follow.

 string xml = @"<?xml version=""1.0"" encoding=""UTF-8""?>
<rss version=""2.0"">
    <channel>
    <title>Twitter public timeline</title>
    <link>http://twitter.com/public_timeline</link>
    <description>Twitter updates from everyone!</description>
    <language>en-us</language>
    <ttl>40</ttl>

    <item>
      <title>yasu_kobayashi: rTwT: @junm : yayaya</title>
      <description>yasu_kobayashi: rTwT: @junm : yayaya</description>
      <pubDate>Tue, 28 Oct 2008 12:04:48 +0000</pubDate>
      <guid>http://twitter.com/yasu_kobayashi/statuses/978829930</guid>
      <link>http://twitter.com/yasu_kobayashi/statuses/978829930</link>

    </item><item>
      <title>FreeGroup: WikiFortio - foobar http://tinyurl.com/5gvttf</title>
      <description>FreeGroup: WikiFortio - foobar
      http://tinyurl.com/5gvttf</description>
      <pubDate>Tue, 28 Oct 2008 12:04:47 +0000</pubDate>
      <guid>http://twitter.com/FreeGroup/statuses/978829929</guid>
      <link>http://twitter.com/FreeGroup/statuses/978829929</link>

    </item></channel></rss>
        ";
            XPathDocument doc = new XPathDocument(new StringReader(xml));
            XPathNavigator nav = doc.CreateNavigator();

            // Compile a standard XPath expression

            XPathExpression expr;
            expr = nav.Compile("/rss/channel/item");
            XPathNodeIterator iterator = nav.Select(expr);

            // Iterate on the node set

            try
            {
                while (iterator.MoveNext())
                {
                    XPathNavigator nav2 = iterator.Current.Clone();
                    nav2.MoveToChild("title","");
                    Console.WriteLine(nav2.Value);
                    nav2.MoveToParent();
                    nav2.MoveToChild("pubDate","");
                    Console.WriteLine(nav2.Value);

                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            Console.ReadKey();

And this is jan's approach working

        XmlDocument doc2 = new XmlDocument();
        doc2.LoadXml(xml);
        XmlNode root = doc2.DocumentElement;

        foreach (XmlNode item in root.SelectNodes(@"/rss/channel/item"))
        {
            Console.WriteLine(item.SelectSingleNode("title").FirstChild.Value);
            Console.WriteLine(item.SelectSingleNode("pubDate").FirstChild.Value);
        }

jan · Accepted Answer · 2008-10-28 13:08:27Z

5

An alternative:

// starts as in Vinko Vrsalovic 's answer
// and not including decent eror handling
XmlDocument doc = new XmlDocument(new StringReader(xml)); 

foreach (XmlNode item in doc.SelectNodes(@"/rss/channel/item"))
{
  Console.WriteLine(item.SelectSingleNode("title").Value);
  Console.WriteLine(item.SelectSingleNode("pubDate").Value);
}

I don't know if this code is slower or bad practice. Please do comment.

I find it more readable than the other one using Navigator and Iterator.

Edit: I use an XmlDocument. An XPathDocument as in Vinko Vrsalovic 's answer doesn't support this way of working, but is a lot faster: (MSDN)

edited Oct 28, 2008 at 13:08

answered Oct 28, 2008 at 12:28

jan

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3 Comments

AnthonyWJones Over a year ago

Unless you have a very large stream which makes loading the content into a document undesirable then this would a reasonable approach and a lot more readable than using an XmlReader.

Vinko Vrsalovic Over a year ago

I like this approach too. But you can't use it with a XPathDocument, you need a XmlNode

jan Over a year ago

My mistake! I meant XmlDocument. But since I can imagine a Twitter rss feed to become very large, I'd go - in this case - for an implementation using XPathDocument too.

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