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POWPF - Catch exceptions in code executed by SimpleMVVM messagebus
 

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    <p>I'm building a WPF application using the <a href="http://simplemvvmtoolkit.codeplex.com/" rel="nofollow">SimpleMVVM framework</a> and I'm having trouble catching exceptions. I use the MessageBus of SimpleMVVM to send a message to another viewmodel. This all works fine, but I noticed that exceptions raised in the code executed by the messagebus get suppressed. Here's what I've got so far:</p> <p>My <code>MainWindow</code> contains a button that fires a <code>TempCommand</code> on the MainWindowViewModel. This command in turn calls the <code>Test</code> method (shown below), which sends out a notification message using the MessageBus of SimpleMVVM.</p> <pre><code>private void Temp() { SendMessage("Temp", new NotificationEventArgs()); } </code></pre> <p>My <code>MainWindow</code> also contains a <code>Frame</code> with content. The ViewModel of this content, <code>CustomerViewModel</code>, has registered to receive these notifications in its constructor:</p> <pre><code>public CustomerDetailsViewModel(ICustomerServiceAgent agent) { RegisterToReceiveMessages("Temp", Temp); } </code></pre> <p>Where the <code>Temp</code> method simply throws an exception:</p> <pre><code>private void Temp(object sender, NotificationEventArgs args) { throw new NotImplementedException("Somewhere, something horrible happened"); } </code></pre> <p>When I debug the application, I clearly see the <code>Temp</code> method being called and the exception being raised. But for some reason, that's all. The application is unaffected and my exception trapping code is unaware of the exception.</p> <p>I trap exceptions in two ways. The first is by handling the event on the <code>Dispatcher</code>:</p> <pre><code>&lt;Application x:Class="MyApp" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" StartupUri="MainWindow.xaml" DispatcherUnhandledException="App_DispatcherUnhandledException"&gt; </code></pre> <p>Where the code-behind looks like:</p> <pre><code>private void App_DispatcherUnhandledException(object sender, DispatcherUnhandledExceptionEventArgs e) { Log("Exception: " + e.Exception.Message); e.Handled = true; } public static void Log(string message) { File.AppendAllText(@"D:\Temp\log.txt", "[" + DateTime.Now.ToString("F") + "] [" + System.Threading.Thread.CurrentThread.ManagedThreadId.ToString() + "] " + message + Environment.NewLine); } </code></pre> <p>This code catches some exceptions, but not all. I found out that WPF suppresses databinding exceptions by default. Because my ViewModels are bounded through the <code>DataContext</code> property on my view, I thought this was the problem. I found <a href="http://tech.pro/tutorial/940/wpf-snippet-detecting-binding-errors" rel="nofollow">this article</a>, which defines a <code>TraceListener</code> that uses the <code>PresentationTraceSources</code> class. Databinding exceptions now get caught, but... Not the exceptions thrown in the code executed through the MessageBus.</p> <p>I've created a solution demonstrating this behavior, it can be downloaded <a href="http://sdrv.ms/11xXVPe" rel="nofollow">here</a>.</p> <p>And this is where I'm stuck. What am I missing? How do I catch these exceptions?</p> <p>Big thanks in advance.</p> <p>JP</p>
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