Question

I’m looking for the best way to create an RSS feed via MVC4 (and/or WebAPI). This post seemed the most applicable http://www.strathweb.com/2012/04/rss-atom-mediatypeformatter-for-asp-net-webapi/. But it was written in the pre-Release days of WebAPI. I’ve used Nuget to bring all packages up-to-date but attempting to build the project tosses:

Error   2   The type or namespace name 'FormatterContext' could not be found (are you missing a using directive or an assembly reference?)  G:\Code\MvcApplication-atomFormatter\MvcApplication-atomFormatter\SyndicationFeedFormatter.cs   38  129 MvcApplication_syndicationFeedFormatter

I’ve found a number of articles explaining that the MediaTypeFormatter has changed significantly since beta but I have found details on the adjustments required to the code snippet in question.

Is there an updated resource showing the construction of an RSSFormatter?

thx

Answer 1

Yes I wrote that tutorial against Beta.

Below is the code updated to RTM version.

One advice, if I may, is that this example uses a simple “whitelist” of concrete types for which RSS/Atom feed is build (in this case my Url model). Ideally in more complex scenarios, you’d have the formatter set up against an interface, rather than a concrete type, and have all Models which are supposed to be exposed as RSS to implement that interface.

Hope this helps.

   public class SyndicationFeedFormatter : MediaTypeFormatter
    {
        private readonly string atom = "application/atom+xml";
        private readonly string rss = "application/rss+xml";

        public SyndicationFeedFormatter()
        {
            SupportedMediaTypes.Add(new MediaTypeHeaderValue(atom));
            SupportedMediaTypes.Add(new MediaTypeHeaderValue(rss));
        }

        Func<Type, bool> SupportedType = (type) =>
        {
            if (type == typeof(Url) || type == typeof(IEnumerable<Url>))
                return true;
            else
                return false;
        };

        public override bool CanReadType(Type type)
        {
            return SupportedType(type);
        }

        public override bool CanWriteType(Type type)
        {
            return SupportedType(type);
        }

        public override Task WriteToStreamAsync(Type type, object value, Stream writeStream, System.Net.Http.HttpContent content, System.Net.TransportContext transportContext)
        {
            return Task.Factory.StartNew(() =>
            {
                if (type == typeof(Url) || type == typeof(IEnumerable<Url>))
                    BuildSyndicationFeed(value, writeStream, content.Headers.ContentType.MediaType);
            });
        }

        private void BuildSyndicationFeed(object models, Stream stream, string contenttype)
        {
            List<SyndicationItem> items = new List<SyndicationItem>();
            var feed = new SyndicationFeed()
            {
                Title = new TextSyndicationContent("My Feed")
            };

            if (models is IEnumerable<Url>)
            {
                var enumerator = ((IEnumerable<Url>)models).GetEnumerator();
                while (enumerator.MoveNext())
                {
                    items.Add(BuildSyndicationItem(enumerator.Current));
                }
            }
            else
            {
                items.Add(BuildSyndicationItem((Url)models));
            }

            feed.Items = items;

            using (XmlWriter writer = XmlWriter.Create(stream))
            {
                if (string.Equals(contenttype, atom))
                {
                    Atom10FeedFormatter atomformatter = new Atom10FeedFormatter(feed);
                    atomformatter.WriteTo(writer);
                }
                else
                {
                    Rss20FeedFormatter rssformatter = new Rss20FeedFormatter(feed);
                    rssformatter.WriteTo(writer);
                }
            }
        }

        private SyndicationItem BuildSyndicationItem(Url u)
        {
            var item = new SyndicationItem()
            {
                Title = new TextSyndicationContent(u.Title),
                BaseUri = new Uri(u.Address),
                LastUpdatedTime = u.CreatedAt,
                Content = new TextSyndicationContent(u.Description)
            };
            item.Authors.Add(new SyndicationPerson() { Name = u.CreatedBy });
            return item;
        }
    }