The .NET Framework has enhanced the ways in which you deal with errors. C#'s mechanism for handling error conditions allows you to provide custom handling for each type of error condition as well as to separate code that identifies errors from the code that handles them.

What is an Exception?

• OutOfMemoryException

• NullReferenceException

• InvalidCastException

• ArrayTypeMismatchException

• IndexOutOfRangeException

• ArithmeticException

• DivideByZeroException

• OverFlowExceptio 

Be Proactive rather than reactive: It is always a better practice to write code in a manner to avoid exceptions rather than catching and handling the same. This approach may not be possible for all kinds of Exception since it is tough to anticipate OutOfMemoryException and avoid the same.

How to Handle Exceptions in .NET 2.0?

Catching an Exception (eating away the exception)

This kind of handling mechanism is the least encouraged one. The problem with the approach given below is that if an exception is caught, it is not logged. This can have serious problems to the application while diagnosing in case of any problem.

Example 3:

try
{
    // Code where we are anticipating the Exception
}
catch (Exception)
{ 
    //Do Nothing
    // Just Eat Away the Exception
}

Re-Throwing an Exception

Example 4:

try
{
// Code where we are anticipating the Exception
}
catch (UnauthorizedAccessException ObjUnAuthorizedException)
{
    ApplicationAccessFailedException ObjApplicationAccessFailedException = new ApplicationAccessFailedException();
    ObjApplicationAccessFailedException.InnerException = ObjUnAuthorizedEnxception;
    throw ObjUnAuthorizedException;
}

Showing an Error Message to User

Example 5

try
{
    // Code where we are anticipating the Exception
}
catch (Exception)
{
    System.Windows.Forms.MessageBox.Show("Error Message: This is the Message shown to the User");
}

The message shown to the user can be an error message, warning message or an Information message.

What are Custom Exceptions? Why do we need them?

Custom Exceptions are exceptions that are created for applying the Business rules of the Application. These exceptions are used to implement the business rules violations of the application.

Definition of Business Rules:

For example: The minimum balance set for Savings A/C in a bank would be different from a Current A/C. Hence, while developing the application for the same the Business rule would be kept as the same.

Violation of Business Rule: Whenever a Violation of Business rule is done, it should be notified and the proper message should be shown to the user. This will be handled by a Custom Exception. Let us illustrate the same with an example.

Example 6

private void ValidateBeforeDebit(float Amount)
{
    {
        if((Balance â€“ Amount ) < MimimumBalanceNeedToHave)
        {
            throw new MimimumBalanceViolationForSavingsAccount("Current TransactionFailed: Mimimum Balance not available");
        }
         Else
        {
            Debit(Amount);
        }
    }
}

We have a method ValidateBeforeDebit (). This method ensures the minimum balance. If there is no minimum balance then a Custom Exception of the type MimimumBalanceViolationForSavingsAccount is thrown. We need to handle the method whenever we call the method.