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.NET Forum / ASP.NET / Web Services / March 2008App wide catchall exception handler
Hi I have a vs2008 winform app that has a start-up form assigned through application framework i.e. no Sub Main. How can I setup a catchall exception handler to my app to catch any unexpected exceptions? Thanks Regards In "Projects properties", select the "Application" tab and the "View Application Events" button. It will create a vb file that allows to handle Application level events including an "UnhandledException" event... > Hi > [quoted text clipped - 5 lines] > > Regards > I have a vs2008 winform app that has a start-up form assigned through > application framework i.e. no Sub Main. Why not? I haven't played with the Application Framework yet and, personally, I /like/ Sub Main. > How can I setup a catchall exception handler to my app to catch > any unexpected exceptions? Apart from the occasional left-field stuff that the Framework throws at you, you shouldn't /have/ any unexpected exceptions. Exceptions are exceptional, not "unexpected". IMHO, this is one of the big weaknesses of .Net. It hands you this big thing called "Exception Handling" on a platter, then leaves /you/ to work out what to do with it. Other languages are far more explicit and actually push you to keep Exception Handling very much in mind as you write your code. Every "entry point" into your code (Sub Main, methods that run on Threads, any action that the user initiates) should have its /own/ Try..Catch constructs. Having a global, "catch-all" Exception Handler is /limited/ in its use, and then mainly as a last-resort, back-stop. The most you can do here is to log the error to a file, somewhere. By the time you get here, the program's teetering on the edge, ready to collapse in a messy heap. There's nothing you can do to recover from (or /Handle/) the exception. You have to do that /much/ closer to the site of the problem. HTH, Phill W. >> I have a vs2008 winform app that has a start-up form assigned through >> application framework i.e. no Sub Main. [quoted text clipped - 30 lines] > HTH, > Phill W. So are you positing that one should put a big Try/Catch around the code in Program.cs rather than putting in event handlers for the Application Unhandled Exception and the Unhandled Thread Exception? While we all agree that our applications should not throw unhandled exceptions, what if it does? RobinS. > While we all agree that our applications should not throw unhandled > exceptions, what if it does? You tell us. If it does throw an unhandled exception, what will your catch-all handler _do_ about it? Log the exception, and then, what?  Signature-------------------------------------------------------------------------------- John Saunders | MVP - Windows Server System - Connected System Developer >> While we all agree that our applications should not throw unhandled >> exceptions, what if it does? > > You tell us. If it does throw an unhandled exception, what will your > catch-all handler _do_ about it? Log the exception, and then, what? throw it, then restart... just like ms's failed initial attempt at sp1 for vista, fail, restart, fail, restart, fail, restart, ad infinitum, ad nauseum... sometimes its good to just give up. >>> While we all agree that our applications should not throw unhandled >>> exceptions, what if it does? [quoted text clipped - 5 lines] > vista, fail, restart, fail, restart, fail, restart, ad infinitum, ad > nauseum... sometimes its good to just give up. If it's unhandled, then your application is probably not in a good enough state for you to know that it makes sense to restart. Depending on what kind of application it is, you're probably better off just not catching such an exception. Signature-------------------------------------------------------------------------------- John Saunders | MVP - Windows Server System - Connected System Developer >> While we all agree that our applications should not throw unhandled >> exceptions, what if it does? > > You tell us. If it does throw an unhandled exception, what will your > catch-all handler _do_ about it? Log the exception, and then, what? Exit, I assume. It is not there to fix things, it is there to avoid a weird message for the user. The message should inform them that the programmer failed to catch the exception, that it has been logged, and that they should have a nice day. >>> While we all agree that our applications should not throw unhandled >>> exceptions, what if it does? [quoted text clipped - 6 lines] > programmer failed to catch the exception, that it has been logged, and > that they should have a nice day. That's exactly right. Plus, it gives us the exception and a stack trace to work off of to fix the problem. That's better than "the application crashed and we have no idea what it did". It also removes the onus on the user to copy the error message and send it to us. More information is always better. RobinS.
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