UnderstandingException Handling in .net.

Presenter: Harsh Wardhan, Mindfire SolutionsDate: 29/10/2013

Presenter: Harsh Wardhan, Mindfire Solutions

Agenda

- What is Exception?- The try, the catch & the finally.- A look into System.Exception class.- Throwing Exception.- Defining your own exception class.- Best practices.- Unhandled Exceptions.- Debugging Exceptions.

Presenter: Harsh Wardhan, Mindfire Solutions

What is Exception?

- When a member fails to complete the task it is supposed to perform as indicated by its name, it is called an exception.

Presenter: Harsh Wardhan, Mindfire Solutions

The Try

- A Try block contains code that require:- Common clean up operations.- Exception recovery operations.- A code that might potentially throw an exception.

- A Try block should have at least one catch or finally block associated with it.

- How much code should be added in a single try block?

Presenter: Harsh Wardhan, Mindfire Solutions

The Catch

- Contains code to execute in response to an exception.

- A try block can have multiple catch blocks.- The expression after Catch keyword is catch

type.- CLR searches the catch type from top to

bottom.

Presenter: Harsh Wardhan, Mindfire Solutions

The Catch

- What to do in a catch block?– Re-throw same exception.– Throw a different exception with richer

exception information to code higher up in the call stack.

– Let the thread fall out of the bottom of the catch block.

Presenter: Harsh Wardhan, Mindfire Solutions

The Finally

- It contains code that's guranteed to execute.- Mostly contains clean up operations required

by actions taken in try block.- Code in catch and finally blocks should be

short and should have likelihood of succeeding without itself throwing an exception.

Presenter: Harsh Wardhan, Mindfire Solutions

A look into System.Exception

- Base class for all exceptions.- All user and system defined exceptions

derive from System.Exception class.- Important Properties of System.Exception:

- Message - Data- Source - Stack-trace- Target Site - Help link- Inner exception

Presenter: Harsh Wardhan, Mindfire Solutions

Throwing Exception

- Points to consider while throwing an exception:– What exception derived type you need

to throw.– What string message are you going to

pass to the exception type's constructor.

Presenter: Harsh Wardhan, Mindfire Solutions

Defining your own Exception class

- Create your exception class when the error is tightly bound to the class issuing the error.

- Your exception class should be shallow and wide.

Presenter: Harsh Wardhan, Mindfire Solutions

Defining your own Exception class

- Best practices for creating Exception class:– Should derive from ApplicationException– Marked with <System.Seralizable>

attribute– Defines a default constructor– Defines a constructor that sets inherited

message property.– Defines a constructor to handle inner

exception.– Defines a constructor for serialization of

your type.

Presenter: Harsh Wardhan, Mindfire Solutions

Best Practices

- Use finally block liberally.– Use finally to clean up from any

operation.– Dispose objects to avoid resource leak.– Examples in our language compiler:• Lock statement.• Using statement.• For each statement.

Presenter: Harsh Wardhan, Mindfire Solutions

Best Practices

- Don't Catch everything.– When you catch an exception you are

actually saying one of these things:• You expected this exeption.• You understand why it occurred.• You know how to deal with it.

Presenter: Harsh Wardhan, Mindfire Solutions

Best Practices

- NEVER leave an empty catch block.- Always try to catch specific exceptions.- Catch a System.Exception and execute some

code inside catch block as long as you re-throw the exception.

Presenter: Harsh Wardhan, Mindfire Solutions

Unhandled Exceptions

- If no catch block matches the thrown exception type, an unhandled exception occurs.

- Usually information gets logged in Event Log.

Presenter: Harsh Wardhan, Mindfire Solutions

Debugging Exceptions

- You can enable the exception to break the flow when it occurs.

- Helps in finding the exceptions being swallowed.

- You can add your own exception.

Presenter: Harsh Wardhan, Mindfire Solutions

Question and Answer

Presenter: Harsh Wardhan, Mindfire Solutions

Thank you