Intercepting an exception inside IDisposable.Dispose

Question

In the IDisposable.Dispose method is there a way to figure out if an exception is being thrown?

using (MyWrapper wrapper = new MyWrapper()) {     throw new Exception("Bad error."); } 

If an exception is thrown in the using statement I want to know about it when the IDisposable object is disposed.

Answer 1

You can extend IDisposable with method Complete and use pattern like that:

using (MyWrapper wrapper = new MyWrapper()) {     throw new Exception("Bad error.");     wrapper.Complete(); } 

If an exception is thrown inside the using statement Complete will not be called before Dispose.

If you want to know what exact exception is thrown, then subscribe on AppDomain.CurrentDomain.FirstChanceException event and store last thrown exception in ThreadLocal<Exception> variable.

Such pattern implemented in TransactionScope class.

Answer 2

No, there is no way to do this in the .Net framework, you cannot figure out the current-exception-which-is-being-thrown in a finally clause.

See this post on my blog, for a comparison with a similar pattern in Ruby, it highlights the gaps I think exist with the IDisposable pattern.

Ayende has a trick that will allow you to detect an exception happened, however, it will not tell you which exception it was.