Is there a way to get the last thrown exception outside of a try/catch block? - vb.net

Question

Edit:
To all answerers and commenters: Please focus on providing the solution I request rather than offer ways to refactor it. The code provided below is a very condensed example for the sake of brevity. I've already stated below that this type of code exists in 20 or 30 places throughout the app and that I am choosing not to move/merge/refactor any of that code if a simpler solution exists.
Original Question:
First, here's brief run-down: We have an app that was developed by an offshore team. The purpose of this application is to run nightly maintenance on various database tables. It is a WinForms app, but it acts more like a console app as all it does is 1) execute a single method in Form1_Load and then 2) call End to shut down the program.
The problem is that the error email notification doesn't work, so I have been charged with the task of fixing it. Consider this code:
Try
'This inner Try/Catch is actually code in another method
Try
'Run some code here
Catch ex As Exception
'Errors are logged silently to text file here
End Try
Catch ex As Exception
'Code to email exception details is here
End Try
The problem is that an exception is thrown and handled in the inner Try/Catch. Because of this, there's no exception to be handled in the outer Try/Catch, hence why no email notification is being sent.
Someone might say to just add Throw ex in the inner Catch, but keep in mind that there are about 20 or 30 places in the code where exceptions are handled like this. The decision I am making is to just get it working for now and not undergo that kind of development effort. Therefore, I seek a way to somehow acquire the last exception thrown by the application. This way, I can add a Finally block to the outer Try/Catch and do something like this:
Finally
If Not Application.GetLastException() is Nothing Then
SendErrorEmail(Application.GetLastException())
End If
End Try

Answer 1

So if I understand this correctly, your application catches all exceptions and logs them silently to a file.
You want to change the behavior so that when the program ends you get the last exception thrown, if any, and send an email with that exception detail. But the last exception thrown isn't stored anywhere.
And you want to change this behavior without modifying the code that handles the exceptions.
That can't be done. How do you expect to change the program's behavior without changing the program's behavior? What you ask is impossible. (And, no, not even Yoda would be able to pull this particular X-wing out of the swamp.)
There is no runtime property that automatically saves the last exception thrown.
You will have to make some modification to the code that catches the exceptions. You say that the code takes this general format:
Try
'This inner Try/Catch is actually code in another method
Try
'Run some code here
Catch ex As Exception
'Errors are logged silently to text file here
End Try
Catch ex As Exception
'Code to email exception details is here
End Try
I take it that the problem is in the inner Catch block. Seems to me that if there's common code to log the errors to a text file, that code should be in a separate method. If it is, then modify that method to save the last exception in a property that can be accessed by your GetLastException method. If there isn't a common method that handles the exception logging then you'll have to make the change at every place.
The commenters are correct: A general "catch all exceptions" is almost always a bad idea. Especially when the "handling" consists of logging and continuing. When you catch some random exception, you have no idea what the state of your program is. It's very likely that the data is corrupt and the program's state is unstable. "Log and continue" just makes the problem worse, and can lead to all kinds of interesting side effects like data corruption, infinite loops, deadlock, etc.
Your best course of action here is to refactor the code. Actually, the best course would be to send it back to the offshore developers and tell them to do it right. But that's probably too much to ask.

Answer 2

I'm quite late to this party but you could try this rather ugly way of doing things.
Firstly extend the Application class by adding a LastException property and a GetLastException function, see here for details.
Secondly add a line to each of the inner Catch blocks and set the LastExcepotion property:
Application.LastException = ex
There you go, no need to refactor all that offshore code.