AppDomain.UnhandledException does not run in all cases by SecurityException1

Additional Information:

I just realized that this behaviour does not occur if you run with the debugger (Debug/Release - Build does not seem to matter). In this case, your delegate will be run (in the example, the MessageBox is shown on click). If you don't run with debugging, the custom MessageBox does not appear, so I conclude that this must be a real bug.
Of course, it's a lot more important to have your handler if you do _not_ run with the debugger attached. ;)

Thank you for your feedback on this issue. By default, unhandled exceptions in a Windows Forms application will display the Unhandled Exception Dialog. You can get the behavior you want by either hooking the Application.ThreadException event (rather than the UnhandledException event) or by setting Application.SetUnhandledExceptionMode(UnhandledExceptionMode.ThrowException) in your Main() method.

The Windows Forms Team

I would like to request for a clearer documentation. For example, in http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfsystemappdomainclassunhandledexceptiontopic.asp there is simply no word about when an exception is candidate for raising the event and when not. There is also no link to http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfsystemwindowsformsapplicationclassthreadexceptiontopic.asp, in which there is also no clear statement what kind of exceptions are raising this event.

Are there any further situations where none of these two handlers will be called? Is there a default handler for all exceptions?


The second thing is that I am still wondering, why in my test project the event is raised when running with the debugger. IMHO it's somewhat confusing if the application behaves completely different when being run with the debugger or not. Especially, custom uncaught exception handling is IMHO not more important when running with the debugger than it is when running without.

Updated the docs for AppDomain.UnhandledException to make it clear that by default the UnhandledException event is preempted in Windows.Forms applications by the ThreadException event, but ONLY for the UI thread. (Also mentioned that this default behavior can be overridden, so that UnhandledException is raised instead of ThreadException.) This will be available in MSDN online next time we upload updated content. Handing the bug off to WinForms to update the other topics.

Updated the ThreadException sample to (1) use SetUnhandledExceptionMode() and (2) show handling errors generated in both Windows Forms main UI thread (ThreadException) and in other threads (AppDomain.UnhandledException). Added new explanatory text to differentiate the two.

Updated the ThreadException sample to (1) use SetUnhandledExceptionMode() and (2) show handling errors generated in both Windows Forms main UI thread (ThreadException) and in other threads (AppDomain.UnhandledException). Added new explanatory text to differentiate the two.

Added sample to App.ThreadException, App.SetUnhandledExceptionMode (all overloads), and UnhandledExceptionMode enum.