Class Library Exception Handling

Question

I have been reading up on exception handling best practices. I'm not sure exactly what is the best way to handle exceptions in the class library. For example, you have a class library with a method that calls private method that updates data in a SQL database so you would normally use a try/catch/finally block to catch the exception if one occurs (very likely). My question is what would the best way to be to handle the exception like re throwing it again with just throw or log the error in a file and return false (bool return method) with a friendly error message? I just want to do it the best way possible.

Mahesh Chand · Answer

Welcome to C# Corner Community Kevin. This is actually an excellent question and I have seen developers implementing exception handling in wrong ways. For instance if you use try..catch in your class library and don't return a proper message to UI your application will have no idea where the error occurred. There are several ways to deal with it. One method I found useful is each of my method in my class library returns the last parameter as ErrorCode which has a message of exact error from the catch block. If there was no error in the class library method always returns by default constant value SUCCCESS. My UI looks if value wasn't success than deal with the error. You can even have your methods return a parameter value null value by default and UI just checks if its null or not. I've also seen throwing exception to the application level is also a good idea but in that case your application developer has to ensure that they are dealing with it. Ofcourse my class library was logging all exceptions in a log file. Use Log4Net for that ;). A free open source project. Hope it gives you some pointers.

kevin · Answer

Thanks for your reply. I have a good understanding now on what I should do. You have been a big help.

Mahesh Chand · Answer

If you have exception handling in your class library your library should never throw an exception since all code will be within try..catch block and you will always get values such as error message or whatever else you are returning. So in the application application will always check what a method returns. What I did in my applications I wrote detailed exception error with class library methods exact error and other details like line of code objects where error occurred etc in the log file and to UI I returned only message I wanted to display to the users and send notifications about the exception to myself. That was for a Web application. So it really depends on if you really want to do some work in the application if exception occurs? To users they wont care of the exception. They care about the error message.

kevin · Answer

What would be the best way if you are returning a value from the method? Would it be best to just create another exception class just for the class library to add a friendly error message but also be able to return the original exception? It would be a generic exception class like for example the class library is called ClassLib so you would create a ClassLibException that the UI can use for when calling certain methods.