MSDN Magazine - January 2008 - (Page 80)

Figure 5 Transforming a Feed // read an ATOM feed Uri feedUri = new Uri(“http://blogs.msdn.com/justinjsmith/atom.xml”); SyndicationFeed feed = SyndicationFeed.Load(feedUri); // transform it to RSS Rss20FeedFormatter formatter = new Rss20FeedFormatter(feed); XmlWriter writer = XmlWriter.Create(Console.Out, null); // write it to the Console formatter.WriteTo(writer); writer.Flush(); Title is just one of many properties you can set, so check the documentation for additional possibilities. It is often the case that you want to read an existing feed and do something based on the contents of that feed. In the new syndication API, you can instantiate a SyndicationFeed and automatically populate its state from an existing feed. All you need to start is the URI of the existing feed or an XmlReader that’s poised to read one. This code shows how to connect to an existing feed on the Web and extract some information from it: Uri feedUri = new Uri(“http://blogs.msdn.com/justinjsmith/atom.xml”); SyndicationFeed feed = SyndicationFeed.Load(feedUri); Console.WriteLine(feed.Title.Text); // outputs “The Cybertopian Chronicle” consume syndicated content with the .NET Framework. Though the new syndication functionality was written by the WCF team, it is not dependent on WCF. In fact, all of the syndication-related types are part of the System.Syndication namespace, though they reside in the System.ServiceModel.Web.dll assembly. You can use the syndication capabilities of the .NET Framework 3.5 The new syndication API from any process that hosts includes types that abstract an AppDomain (ASP.NET, an individual syndication WPF applications, NT Services, and so on). This feed and the items in a feed, capability implies that you as well as types that can can serve or consume syntransform that feed into a dicated content over any particular format. transport, not just HTTP. However, when coupled with the HTTP programming model in WCF, you can add syndication to existing SOAP/WS-* services as well. The new syndication API includes types that abstract an individual syndication feed and the items in a feed, as well as types that can transform that feed into a particular format. The System.Syndication.SyndicationFeed type is a format-neutral representation of a syndication feed. A SyndicationFeed contains a list of SyndicationItem objects. A SyndicationFeed without a set of SyndicationItem objects is like a pod without any peas, because a SyndicationItem object is just a representation of an item in a feed. Once a SyndicationFeed has been populated with a set of SyndicationItem objects, a SyndicationFeedFormatter can transform that feed into a particular format. There are two types derived from SyndicationFeedFormatter : Rss20FeedFormatter and Atom10FeedFormatter. As their names imply, these types transform an instance of a SyndicationFeed into the RSS 2.0 and ATOM 1.0 formats, respectively. The SyndicationItem type contains more than 35 members. Many of these are properties related to setting or retrieving fields like the item identifier, last updated time, published date, title, or the actual content. There are also numerous members that make it easy to extend the content stored in a SyndicationItem. There are many extensions to RSS and ATOM (Microsoft Simple List Extensions, Yahoo Media RSS, and GeoRSS, among many others), and both SyndicationFeed and SyndicationItem can be extended to include any existing RSS or ATOM extension. Feeds can have many items, and loading them all at once is not an option for large feeds. The SyndicationFeed addresses this situation by exposing its set of SyndicationItem object as an IEnumerable . This implementation makes it easier to deal with large numbers of SyndicationItem objects because it leverages the iterator capability of the .NET Framework 2.0. It’s also possible to iterate over a set of SyndicationItem objects using LINQ. This can dramatically reduce the amount of code required to extract information from a feed. The syndication API defines several types that transform a SyndicationFeed into the RSS 2.0 and ATOM 1.0 formats. In fact, you Figure 6 Exposing a Feed from a Customized URI [ServiceKnownType(typeof(Atom10FeedFormatter))] [ServiceKnownType(typeof(Rss20FeedFormatter))] [ServiceContract] interface IPictureService { [OperationContract] [WebGet(UriTemplate=“Pictures?format={format}”)] SyndicationFeedFormatter Feed(String format); } class PictureService : IPictureService { public SyndicationFeedFormatter Feed(String format){ // create the syndication feed SyndicationFeed feed = new SyndicationFeed(); // add the items to the feed (omitted) // check the argument & return the right format if(format.ToLower() == “rss”){ return new Rss20FeedFormatter(feed); } return new Atom10FeedFormatter(feed); } } Creating a SyndicationFeed There are two ways to create a SyndicationFeed object. You can instantiate one and populate its members manually, or you can populate the entire SyndicationFeed from an existing feed. Both are easy to do and shield the developer from the quirks of a particular wire format. This code demonstrates how to build a SyndicationFeed object manually. SyndicationFeed feed = new SyndicationFeed(); feed.Title.Text = “The Cybertopian Chronicle”; 80 msdnmagazine WCF Syndication

Table of Contents Feed for the Digital Edition of MSDN Magazine - January 2008

MSDN Magazine - January 2008 Contents Toolbox CLR Inside Out Data Points Advanced Basics Cutting Edge IIS 7.0 - Enhance Your Apps with the Integrated ASP.NET Pipeline World Ready - Around the World with ASP.NET AJAX Applications WCF Syndication - HTTP Programming with WCF and the .NET Framework 3.5 Wicked Code Foundations Extreme ASP.NET {End Bracket}

MSDN Magazine - January 2008

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