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copied!<p>Questions like this seem to behave like buses. You don't see any for ages then two come along almost at the same time. See this <a href="https://stackoverflow.com/questions/5537918/silverlight-httpwebrequest-syncronous-call/5538448#5538448">answer</a> to a more concrete version of this question asked earlier today.</p> <p>I have to I agree with you, continuation passing is tricky. A really useful technique is to borrow the C# <code>yield return</code> construct to create a machine that is able to maintain state between asynchronous operations. For a really good explanation see this <a href="http://csharperimage.jeremylikness.com/2010/03/sequential-asynchronous-workflows-in.html" rel="nofollow noreferrer">blog</a> by Jeremy Likness.</p> <p>Personally I prefer a "less is more" approach so the <a href="http://geekswithblogs.net/codingbloke/archive/2010/09/12/simple-asynchronous-operation-runner-ndash-part-1.aspx" rel="nofollow noreferrer">AsyncOperationService</a> is a very small chunk of code. You'll note that it has a single callback for both success and failure and there no interfaces to implement just a moderate delegate <code>Action<Action<Exception>></code> which is typed as <code>AsyncOperation</code> to make it more convenient.</p> <p>The basic steps to coding against this are:-</p> <ul> <li>Code as if synchronous execution were possible</li> <li>Create methods that return an <code>AsyncOperation</code> fpr only the smallest part that has to be asynchronous. Usually some <code>WebRequest</code> or WCF call but note just enough to get past the async bit, see me other answer for a good example.</li> <li>Convert the synchronous "psuedo-code" to <code>yeild</code> these AsyncOperations and change the calling code to "Run" the resulting enumerable.</li> </ul> <p>The final code looks quite similar to the synchronous code you might be more familar with.</p> <p>As to accidentally running things on a background thread, that last answer included this useful AsyncOperation:-</p> <pre><code>public static AsyncOperation SwitchToUIThread() { return (completed => Deployment.Current.Dispatcher.BeginInvoke(() => completed(null))); } </code></pre> <p>You can use that as the final <code>yield</code> in the run to ensure that code executing in the <code>completed</code> callback is executing on the UI thread. Its also useful to "flip" what is apparently synchronous code to be running on the UI thread when necessary.</p>

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