Reading RSS items on Windows Phone 7

Following is a utility class I wrote to help me read RSS items asynchronously on a Silverlight for Windows Phone 7 application.

I will present how it was written and then how to use it. At the end of this post you can find a sample application that contains all the code.

How to read RSS?

Add Helper Assembly

The first thing we need to do is to add a reference to the assembly, System.ServiceModel.Syndication.dll which contains classes that can parse RSS feeds.

This assembly is part of the Silverlight 3 SDK. It isn’t part of the Windows Phone 7 SDK, but there is no problem in using it there. You can find the file under: %ProgramFiles%\Microsoft SDKs\Silverlight\v3.0\Libraries\Client\System.ServiceModel.Syndication.dll

You will get the following warning, just ignore it, it works.

Define RssItem

Before we get to business, let’s define a model class that will encapsulate the data of a single RSS item.

Our RssItem class will hold the following properties: Title, Summary, PublishedDate and Url. In addition I provide a PlainSummary property that will hold a plain text version of the RSS item. Usually the summary has HTML tags that we just want to ignore, thus PlainSummary for the rescue.

/// <summary>
/// Model for RSS item
/// </summary>
public class RssItem
{
    /// <summary>
    /// Initializes a new instance of the <see cref="RssItem"/> class.
    /// </summary>
    /// <param name="title">The title.</param>
    /// <param name="summary">The summary.</param>
    /// <param name="publishedDate">The published date.</param>
    /// <param name="url">The URL.</param>
    public RssItem(string title, string summary, string publishedDate, string url)
    {
        Title = title;
        Summary = summary;
        PublishedDate = publishedDate;
        Url = url;

        // Get plain text from html
        PlainSummary = HttpUtility.HtmlDecode(Regex.Replace(summary, "<[^>]+?>", ""));
    }

    /// <summary>
    /// Gets or sets the title.
    /// </summary>
    /// <value>The title.</value>
    public string Title { get; set; }

    /// <summary>
    /// Gets or sets the summary.
    /// </summary>
    /// <value>The summary.</value>
    public string Summary { get; set; }

    /// <summary>
    /// Gets or sets the published date.
    /// </summary>
    /// <value>The published date.</value>
    public string PublishedDate { get; set; }

    /// <summary>
    /// Gets or sets the URL.
    /// </summary>
    /// <value>The URL.</value>
    public string Url { get; set; }

    /// <summary>
    /// Gets or sets the plain summary.
    /// </summary>
    /// <value>The plain summary.</value>
    public string PlainSummary { get; set; }
}

Implement The RSS service

The RSS service will get the RSS feed URL as a parameter. In addition, since we want our class to work asynchronously we will accept as parameters a few more delegates:

• Action<IEnumerable<RssItem>> onGetRssItemsCompleted, which will be called when the RSS items are ready to be processed.
• Action<Exception> onError, which will be called if there is an error while getting the RSS items.
• Action onFinally, which will be called always, whether there was an exception or not. Think of it as the finally section a common try-catch block.

So the method signature will be:

public static void GetRssItems(string rssFeed, 
    Action<IEnumerable<RssItem>> onGetRssItemsCompleted = null, 
    Action<Exception> onError = null, Action onFinally = null)

To get the feed XML we will use the WebClient class:

WebClient webClient = new WebClient();

// register on download complete event
webClient.OpenReadCompleted += delegate(object sender, OpenReadCompletedEventArgs e)
{
    ...
};

webClient.OpenReadAsync(new Uri(rssFeed));

The actual RSS parsing is done using the SyndicationFeed class from our helper assembly:

// convert rss result to model
List<RssItem> rssItems = new List<RssItem>();
Stream stream = e.Result;
XmlReader response = XmlReader.Create(stream);
SyndicationFeed feeds = SyndicationFeed.Load(response);
foreach (SyndicationItem f in feeds.Items)
{
    RssItem rssItem = new RssItem(f.Title.Text, f.Summary.Text, f.PublishDate.ToString(), 
        f.Links[0].Uri.AbsoluteUri);
    rssItems.Add(rssItem);
}

The rest of the code is for handling the different delegates: onCompleted, onError and onFinally. I bring here the method in its full:

/// <summary>
/// Gets the RSS items.
/// </summary>
/// <param name="rssFeed">The RSS feed.</param>
/// <param name="onGetRssItemsCompleted">The on get RSS items completed.</param>
/// <param name="onError">The on error.</param>
public static void GetRssItems(string rssFeed, 
    Action<IEnumerable<RssItem>> onGetRssItemsCompleted = null, 
    Action<Exception> onError = null, Action onFinally = null)
{
    WebClient webClient = new WebClient();

    // register on download complete event
    webClient.OpenReadCompleted += delegate(object sender, OpenReadCompletedEventArgs e)
    {
        try
        {
            // report error
            if (e.Error != null)
            {
                if (onError != null)
                {
                    onError(e.Error);
                }
                return;
            }

            // convert rss result to model
            List<RssItem> rssItems = new List<RssItem>();
            Stream stream = e.Result;
            XmlReader response = XmlReader.Create(stream);
            SyndicationFeed feeds = SyndicationFeed.Load(response);
            foreach (SyndicationItem f in feeds.Items)
            {
                RssItem rssItem = new RssItem(f.Title.Text, f.Summary.Text, 
                    f.PublishDate.ToString(), f.Links[0].Uri.AbsoluteUri);
                rssItems.Add(rssItem);
            }

            // notify completed callback
            if (onGetRssItemsCompleted != null)
            {
                onGetRssItemsCompleted(rssItems);
            }
        }
        finally
        {
            // notify finally callback
            if (onFinally != null)
            {
                onFinally();
            }
        }
    };

    webClient.OpenReadAsync(new Uri(rssFeed));
}

Using the RSS Service

Using the class is very easy, just provide the URL as the first parameter and a delegate for getting the “completed” notification.

private void Button_Click(object sender, RoutedEventArgs e)
{
    RssService.GetRssItems(
        WindowsPhoneBlogPosts,
        (items) => { listbox.ItemsSource = items; },
        (exception) => { MessageBox.Show(exception.Message); },
        null
        );
}

There is a sample application which can be downloaded here.

Note: this code was first published as part of the “Using Pivot and Panorama Controls” lab found in the Windows Phone Training Kit for Developers, which I wrote for Microsoft.

That’s it for now, Arik Poznanski.