Test if ther was a Exception in last method call

Prev Maxwel

Hi there,

I got some Code like:

After calling this method I want to test in the next method if there was an Exception.
And if so do something to react on this Exception.

Is there a way to do so?

9 Replies

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Vulpes15y ago
No, I don't think what you are trying to do is possible.

To prevent the application from terminating, an exception has to be caught in the method in which it arises, in the method which calls that method or in another method lower down the call stack.

Otherwise, you can use one the 'last chance' exceptions to log it and attempt some clean up before the application terminates.

The only way to do anything remotely like you want would be to write your methods to return error codes for non-fatal errors, rather than throw exceptions. You could then log these errors either to a file or to a global collection within memory and the code would continue execution.

A subsequent method could then check the file or collection, to see whether an error arose in the method in question and react to it.

Needless to say, if you did something like this, you'd have to make sure that non-fatal errors didn't throw .NET Framework exceptions as well, because those exceptions would have to be caught earlier in the call stack to prevent the application from terminating.
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Prev Maxwel15y ago
Ok, more description is needed:

The "Main" application is a run-engine that is using the methods mentioned above.
Some of the methods are generated automatically (and therefore should not be changed). These methods are like Method 1. If there is an exception the run-engine logs this (this is one of the main purposes of it!) The Application does not terminate.

Now after a method of Type 1 a "CleanUp" is needed in a Method Type 2 depends on the fact if a exception occurs in the Type 1 Method.

But I see it I nor really Possible what I want to …
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Vulpes15y ago
All exceptions terminate an application with the appropriate message if they're not caught. This is why C# has try/catch/finally to prevent exceptions, which can be recovered from, bringing down the application.

The UnhandledException exception (and several other 'last chance' exceptions in the .NET Framework) are provided as a fall-back to allow you to log the exception and perhaps attempt some clean up before the application terminates.

All that handling the FirstChanceException does is to notify you that an exception has occurred. If it's not caught within another exception handler, then it will still cause the application to terminate.

If an exception leaves a process in an unstable state, then any attempt to handle it may lead to unreliable results. You should therefore only use the HandleProcessCorruptedStateExceptionsAttribute attribute if it's critical that you attempt to do some cleanup such as saving a file before the application terminates.
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Prev Maxwel15y ago
A handler for the AppDomain.UnhandledException catches an exception which is not otherwise caught, offering the opportunity to at least log it, before the application is terminated. However, it is not possible to prevent termination which occurs immediately after the handler has run.

What if the exception wouldn't terminate the application?
The Methods are executed using a test engine, and the exception is logged in the results.
But this time I've to check in method2 if there was a exception in Method1.
The AppDomain.FirstChanceException provides a notification that an exception has occurred but doesn't actually handle it. The runtime searches for another eventhandler to do that. It therefore gives you the opportunity to examine any exceptions before they are handled or not.

This is sounds good.
But looking throug the code examples ()
I think I would also have to change code in methode 1 ...

Also, if you're using .NET 4.0, you have to mark the eventhandlers for both these exceptions with the HandleProcessCorruptedStateExceptionsAttribute attribute if you want to catch an exception such as a stack overflow or access violation which corrupts the state of the process.
Hmm ...
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Vulpes15y ago
A handler for the AppDomain.UnhandledException catches an exception which is not otherwise caught, offering the opportunity to at least log it, before the application is terminated. However, it is not possible to prevent termination which occurs immediately after the handler has run.

The AppDomain.FirstChanceException provides a notification that an exception has occurred but doesn't actually handle it. The runtime searches for another eventhandler to do that. It therefore gives you the opportunity to examine any exceptions before they are handled or not.

Also, if you're using .NET 4.0, you have to mark the eventhandlers for both these exceptions with the HandleProcessCorruptedStateExceptionsAttribute attribute if you want to catch an exception such as a stack overflow or access violation which corrupts the state of the process.
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Prev Maxwel15y ago
Found something like This:
System.AppDomain.UnhandledException & System.AppDomain.FirstChanceException.

Not sure if this is the right, cause im very new to C#.
But maybe it is ok.
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Prev Maxwel15y ago
No, this is explicitly not the approach I'm looking for. I want to react in another method on the exception. Without changing in methode 1.
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Morcos Adel15y ago
i think you should call this method in the next method like you say and put it between a try{} and catch(){}
this could approach what you're looking for
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Vulpes15y ago
You'll need to wrap the call to DoTest1() in a try/catch/finally block:

try
{
DoTest1();
}
catch(Exception ex)
{
// do something depending on exception type
}
finally
{
// if required
}

It will help, of course, if you know what types of exceptions DoTest1() might throw so you can catch those exception types specifically.
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