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POGlobally catch exceptions thrown from WCF async calls in a background thread
 

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    <p>I have a WPF application that communicates with a WCF service. I'm currently calling my WCF service from my ViewModels (I'm using the MVVM pattern) using the following <code>async</code> based pattern:</p> <pre><code>public async override void MyCommandImplementation() { using (var proxy = new MyProxy()) { var something = await proxy.GetSomethingAsync(); this.MyProperty = something; } } </code></pre> <p>As I'm following the MVVM pattern, I have <code>ICommand</code> public properties that are exposed by my ViewModels, so associated command implementation won't return <code>Task&lt;T&gt;</code> objects as they are like event handlers. So the exception handling is actually pretty simple, i.e. I am able to catch any exception thrown from my WCF service using the following pattern:</p> <pre><code>public async override void MyCommandImplementation() { try { using (var proxy = new MyProxy()) { var something = await proxy.GetSomethingAsync(); } } catch (FaultException&lt;MyFaultDetail&gt; ex) { // Do something here } } </code></pre> <p>So far so good, everything work as expected if the server throws an exception that is automatically converted to a SOAP Fault thanks to a custom WCF behavior.</p> <p>As I have some common exceptions that can be thrown everywhere in my service (for instance each WCF operation can throw a <code>AuthenticationException</code> that'll by converted on client side to a <code>FaultException&lt;AuthenticationFaultDetail&gt;</code> exception), I've decided to handle some exceptions in a common place in my application, i.e. by handling the <code>Application.DispatcherUnhandledException</code> event. This works just fine, I can catch all my <code>FaultException&lt;AuthenticationFaultDetail&gt;</code> exceptions everywhere, display an error message to the user, and prevent the application from exiting:</p> <pre><code>private static void Application_DispatcherUnhandledException(object sender, DispatcherUnhandledExceptionEventArgs e) { // Exception handler that handles some common exceptions // such as FaultException&lt;AuthenticationFaultDetail&gt; if (GlobalExceptionHandler.HandleException(e.Exception)) { // Expected exception, so we're fine e.Handled = true; } else { // We're not fine. We couldn't handle the exception // so we'll exit the application // Log...etc. } } </code></pre> <p>Everything works pretty well because <code>FaultException</code> are thrown in the UI thread thanks to the <code>async</code> pattern and the synchronization context switch before/after the <code>await</code> keyword.</p> <p>My problem is, other exception can be thrown in another thread than my UI thread, for example in case of <code>EndPointNotFoundException</code> thrown at the <code>await proxy.GetSomethingAsync();</code> line (case of WCF service shutdown on server side).</p> <p>Those exceptions won't be handled in the <code>Application.DispatcherUnhandledException</code> event handler because they are not thrown in the UI thread. I can handle them in the <code>AppDomain.UnhandledException</code> event, but I'm not able to do anything else than do some logging and exit the application (there is basically no "e.Handled"-like property).</p> <p>So my question is: how could I handle exceptions thrown in background threads in case of an async WCF call in one place of my application?</p> <p>The best I can think of right now is something like the following:</p> <pre><code>public class ExceptionHandler : IDisposable { public void HandleException(Exception ex) { // Do something clever here } public void Dispose() { // Do nothing here, I just want the 'using' syntactic sugar } } ... public async override void MyCommandImplementation() { using (var handler = new ExceptionHandler()) { try { using (var proxy = new MyProxy()) { var something = await proxy.GetSomethingAsync(); } } catch (FaultException&lt;MyFaultDetail&gt; ex) { // Do something here } catch (Exception ex) { // For other exceptions in any thread handler.HandleException(ex); } } } </code></pre> <p>But this would require me to refactor a lot of code (each time I asynchronously call a web service).</p> <p>Any idea that would allow me to <em>not</em> refactor a huge amount of code would be helpful.</p>
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