Silverlight RSS Part I (Simple RSS reader)

Latest posts from SilverlightTips.com

Displaying a RSS feed is a very straight forward task in Silverlight.

In summary: we need to access and download the RSS (XML file) and read it as a single string value, read the downloaded string as XML using XmlReader class, load the XML into a variable of type SyndicationFeed, and finally using a loop extract each node and save it in a desirable variable.

Some of the Silverlight built-in classes used in this example are:

Uri:	Takes the URL of the RSS feed
XmlReader:	Represents a reader that provides fast, non-cached, forward-only access to XML data” (msdn)
SyndicationFeed:	Represents a top-level feed object, <feed> in Atom 1.0 and <rss> in RSS 2.0” (msdn)
WebClient:	Receives data from a recource defuned by Uri (in our case a URL to RSS or XML file)

I am going to demonstrate how to read and display a RSS feed (XML file) in three simple steps:

Step 1: Create a custom RSS class
here I am just creating a new public class (RSSItem) for my RSS feed to contain any information I would like to keep for each item in the RSS. This will help to keep my project tidy and my code meaningful. In my RSSItem class I will add as many properties as I need:

public class RSSItem
{
    #region Properties
    public string RSSTitle {get; set;}
    public string RSSDescription { get; set; }
    public Uri RSSLink { get; set; }
    #endregion
}

Step 2: Reading the RSS feed in Silverlight
create three private variables for Uri, XmlReader and SyndicationFeed (for this you need to add a new reference in your project to System.ServiceModel.Syndication – do this by right clicking on ‘References’ folder in you Silverlight project and clicking on ‘Add Reference...’)

private Uri rssUri;
private XmlReader xmlReader;
private SyndicationFeed feed;

and don't forget to add the namespaces:

using System.Xml;
using System.ServiceModel.Syndication;

Now, in your constructor or ‘Loaded’ method add the following:

rssUri = new Uri("http://feeds.feedburner.com/Silverlighttips");
WebClient client = new WebClient();
client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(client_DownloadStringCompleted);
client.DownloadStringAsync(rssUri);

WebClient is another built-in class in Silverlight and is used to open the XML (RSS). Since the operation is done asynchronously the callback method (DownloadStringCompleted) is called after the operation is done.

Step 3: Populate RSS nodes
first, add an ItemsControl in the MainPage.xaml:

In the ItemsControl we can bind the required properties from our RSSItem class using {Binding nameOfProperty}.

Now, from our DownloadStringCompleted method in MainPage.xaml.cs we can retrieve the RSS in form of a string. Then, we can create our XmlReader and load it to a SyndicationFeed variable which treats the XML as a 'RSS' and allow us to use its properties:

private void client_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
{
    if (e.Error == null)
    {
        int itemsCount = 5;
        xmlReader = XmlReader.Create(new StringReader(e.Result));
        feed = SyndicationFeed.Load(xmlReader);

        List<RSSItem> itemsList = new List<RSSItem>();

        if (feed.Items.Count() < 5)
        {
            itemsCount = feed.Items.Count();
        }

        for (int i = 0; i <= itemsCount; i++)
        {
            RSSItem rssitem = new RSSItem();
            rssitem.RSSTitle = feed.Items.ToList()[i].Title.Text;
            rssitem.RSSLink = feed.Items.ToList()[i].Links[0].Uri;
            itemsList.Add(rssitem);
        }
        RSS.ItemsSource = itemsList;
    }
}

you will need to add the namespace for the StringReader:

using System.IO;

In the above method from top:

check if there are any errors in the result, if not continue
set the number of items to read
load the XML into a SyndicationFeed variable
create a new List of type RSSItem to hold each RSSItem
if the number of total RSS items to be found (itemsCount) is greater than the total number of RSS items available then go with the total number of available items
search in each node for ‘Title’ and ‘Summary’ (description)
add Title and Summary of each RSS item to the variable of type RSSItem class, and finally add the rssitem to the RSSItem list
at the end we bind our itemsList to 'RSS' which is an ItemsControl in our XAML page

Posted by Damon Serji on 29. November 2009 14:52 under: Intermediate

with 6 Comments

Share this post on: