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.NET Forum / .NET Framework / New Users / October 2007Exception Handling
I have a third party class library (C#) that I am expanding and using with an application (VB.NET) and I am having trouble catching exceptions in the application. The class library has an exception handler that it calls: catch (Exception ex) { _sSessionId = null; objUtils.HandleException("Error: Could not login: " + ex.Message); return ""; } The handler then throws an exception (the one my application should catch): throw new Exception(Environment.NewLine + strMessage); My application has a typical try/catch block but it does not catch the thrown exception; here Login is in the class library: Try strSessionID = oVR.Login() Catch ex As Exception MsgBox(ex.ToString) End Try I am pretty new to exception handling so perhaps I am misunderstanding, can someone point me in the right direction please? Sid. Here is a very good article. http://blogs.msdn.com/kcwalina/archive/2005/03/16/396787.aspx However, your third party class may be breaking the rules. I don't see what you're doing wrong though. try // do someting catch (Exception ex) MessageBox.Show (ex.Message) end try How "robust" or trustworthy is the third party code? Is is a "big" vendor. Or something somebody threw together. >I have a third party class library (C#) that I am expanding and using with >an application (VB.NET) and I am having trouble catching exceptions in the [quoted text clipped - 34 lines] > > Sid. Thank you for the Blog URL, interesting reading. I have the source for the class library and the code clips I included were directly from that source. What could they be doing wrong? Basically in a method of the class library on an exception they call an exception handler, that handler then throws an exception that my application fails to catch. Looking at a call stack: MyApplication ----> Method in Library ---> On an exception it calls an exception handler ---> throws an exception (not caught by MyApplication. Is this breaking the rules? Should I change the library to simply throw exceptions that my application should catch? Thanks again, Sid. > Here is a very good article. > [quoted text clipped - 55 lines] >> >> Sid. No you shouldn't. Your code should catch the exception. How do you know it isn't catching the exception? Put a break point inside the handler and run the application. It should catch.  SignatureRegards, Alvin Bruney ------------------------------------------------------ Shameless Author Plug OWC Black Book 2nd Edition Exclusively on www.lulu.com/owc $24.99 > Thank you for the Blog URL, interesting reading. > [quoted text clipped - 70 lines] >>> >>> Sid. If I put a breakpoint in the handler of the class library it gets hit, however, a breakpoint where my application should catch the exception thrown by the handler is never hit. Sid. > No you shouldn't. Your code should catch the exception. How do you know it > isn't catching the exception? Put a break point inside the handler and run [quoted text clipped - 74 lines] >>>> >>>> Sid. It sounds like something between the exception being thrown in the class library and the application's use of it is catching the exception. Therefore, it doesn't bubble up to the application. SignatureHTH, Kevin Spencer Chicken Salad Surgeon Microsoft MVP > If I put a breakpoint in the handler of the class library it gets hit, > however, a breakpoint where my application should catch the exception [quoted text clipped - 80 lines] >>>>> >>>>> Sid. Kevin, Thanks for the reply; is it okay that the class library to throw an exception that is caught with its own handler and then for that handler to throw another exception for the user to catch? Nested exceptions being thrown. Sid. > It sounds like something between the exception being thrown in the class > library and the application's use of it is catching the exception. [quoted text clipped - 84 lines] >>>>>> >>>>>> Sid. Not a problem at all, if used correctly. A class library should throw exceptions unless it can handle them gracefully. My class libraries include exception handlers that log the details of the exceptions and then throw them routinely. The logging is optional, and can be turned off if desired, but I find it very useful in diagnosing problems. SignatureHTH, Kevin Spencer Chicken Salad Surgeon Microsoft MVP > Kevin, > Thanks for the reply; is it okay that the class library to throw an [quoted text clipped - 92 lines] >>>>>>> >>>>>>> Sid. What is describe is exactly what I am trying to achieve, if only I could figure out why my application is not catching the exceptions, Sid. > Not a problem at all, if used correctly. A class library should throw > exceptions unless it can handle them gracefully. My class libraries [quoted text clipped - 98 lines] >>>>>>>> >>>>>>>> Sid.
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