How do I wrap a MVVM Light ViewModel in a try catch statement?

3
votes

I currently have an AppDomain.CurrentDomain.UnhandledException handler that emails me a stack trace when an application crashes. This is working fine for the most part, but when I get an exception in a MVVM light viewmodel the stack traces can be rather cryptic and not really tell me where they are occurring. Is there a simple way to wrap my viewmodels in a try catch statement that I can then inject some more useful information into the exception and then re-throw it?

The following is an example of the stack trace:

   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
   at GalaSoft.MvvmLight.Helpers.WeakAction.Execute() in d:\GalaSoft\mydotnet\MvvmLight\Source\GalaSoft.MvvmLight\GalaSoft.MvvmLight (NET35)\Helpers\WeakAction.cs:line 269
   at GalaSoft.MvvmLight.Command.RelayCommand.Execute(Object parameter) in d:\GalaSoft\mydotnet\MvvmLight\Source\GalaSoft.MvvmLight\GalaSoft.MvvmLight (NET35)\Command\RelayCommand.cs:line 167
   at MS.Internal.Commands.CommandHelpers.CriticalExecuteCommandSource(ICommandSource commandSource, Boolean userInitiated)
   at System.Windows.Controls.Primitives.ButtonBase.OnClick()
   at System.Windows.Controls.Button.OnClick()
   at System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
   at System.Windows.UIElement.OnMouseLeftButtonUpThunk(Object sender, MouseButtonEventArgs e)
   at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
   at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
   at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
   at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
   at System.Windows.UIElement.ReRaiseEventAs(DependencyObject sender, RoutedEventArgs args, RoutedEvent newEvent)
   at System.Windows.UIElement.OnMouseUpThunk(Object sender, MouseButtonEventArgs e)
   at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
   at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
   at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
   at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
   at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
   at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
   at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
   at System.Windows.Input.InputManager.ProcessStagingArea()
   at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
   at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
   at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
   at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at System.Windows.Interop.HwndSource.InputFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
   at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
   at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
   at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
   at System.Windows.Threading.Dispatcher.Run()
   at System.Windows.Application.RunDispatcher(Object ignore)
   at System.Windows.Application.RunInternal(Window window)
   at System.Windows.Application.Run(Window window)
   at System.Windows.Application.Run()
   at MyApplication.App.Main() in c:|my computer\my projectname\obj\x86\Debug\App.g.cs:line 0
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

This was caused by a NotImplementedException in a method in my viewmodel that was wrapped in a RelayCommand so I could bind a button to it. There is nothing that I can figure out that points me to the name of the method or the name of the viewmodel.

2
c#wpfmvvmexception-handlingmvvm-light
Could you show one of those cryptic exceptions? – Daniel Hilgarth
Stack trace has been added. The only thing I edited was he name of my application and the line that had the path to the overall project in it. – PlTaylor
Does that exception have an InnerException? – Daniel Hilgarth
Yes it does...and that has significantly more pertinent info! Thanks for pointing out what should have been obvious. If you write this up as an answer I will mark it as such – PlTaylor
The fact that the code will make my error messages easier to read makes me smile. – PlTaylor

2 Answers

6
votes

You should have more info in the InnerException property.

If I am not mistaken, your main exception is of type TargetInvocationException. You could write a little method that unwraps this:

public Exception Unwrap(TargetInvocationException root)
{
    if(root.InnerException == null)
        return root;
    var innerException = root.InnerException as TargetInvocationException;
    if(innerException == null)
        return root.InnerException;

    return Unwrap(innerException);
}

This method is helpful, because often you have multiple levels of TargetInvocationException with the real exception burried under 3 or 4 of them.

0
votes

If you're handling the AppDomain.CurrentDomain.UnhandledException event already, can you not add your information in that handler?:

public void MainWindow_UnhandledException(object sender, UnhandledExceptionEventArgs e)
{
    Exception exception = (Exception)e.ExceptionObject;
    if (exception.TargetSite.Module.ToString() == "nameOfViewModelAssembly.dll")
    {
        if (exception.StackTrace.Contains(nameOfSomeViewModel))
        {
            throw new Exception("Problem in nameOfSomeViewModel", exception);
        }
        else if (exception.StackTrace.Contains(nameOfOtherViewModel))
        {
            throw new Exception("Problem in nameOfOtherViewModel", exception);
        }
    }
}

Of course, this could get quite big if you have a lot of view models, but I'm sure you could find a more efficient way to do this.