Question

I’m trying to put together a simple RSS feed reader in windows phone 7 but I’m struggling to understand how the async model works.

What I have is a helper class that when I pass it a URL will parse and build up a ViewModel object and return it. So what I am trying to acheive is this:

public static class FeedHelper
{
   public static FeedViewModel LoadFeed(string url)
   {
      //parse rss feed and return view model
   }
}

In the loadfeed method I would make a webclient object and build up the FeedViewModel. However because the WebClient’s DownloadStringAsync is async and the result is returned to another method I can’t figure out how I can return the FeedViewModel from my LoadFeed method.

Any examples or links to blog posts would be appreciated. I’ve done quite a bit of googling but can’t find any examples of how I would approach this problem.

Answer 1

You cannot return the ViewModel from your LoadFeed function because as you discovered, the call is async.

You have several choices, for ex. you could:

• make the LoadFeed method non-static and put it into a class (for ex. FeedRetriever)
• in the FeedRetriever class expose an event (or a command) “FeedLoaded”
• in your ViewModel repository subscribe to that event/command and take the ViewModel in the handler