Learning C#

Custom Exceptions

The intrinsic exception types the CLR provides, coupled with the custom messages shown in the previous example, will often be all you need to provide extensive information to a catch block when an exception is thrown.

There will be times, however, when you want to provide more extensive information or need special capabilities in your exception. It is a trivial matter to create your own custom exception class; the only restriction is that it must derive (directly or indirectly) from System.ApplicationException. Example 18-7 illustrates the creation of a custom exception.

Example 18-7. A custom exception

using System; namespace ExceptionHandling { // custom exception class public class MyCustomException : System.ApplicationException { public MyCustomException(string message): base(message) // pass the message up to the base class { } } class Tester { public void Run() { try { Console.WriteLine("Open file here"); double a = 0; double b = 5; Console.WriteLine ("{0} / {1} = {2}", a, b, DoDivide(a,b)); Console.WriteLine ( "This line may or may not print"); } // most derived exception type first catch (System.DivideByZeroException e) { Console.WriteLine( "\nDivideByZeroException! Msg: {0}", e.Message); Console.WriteLine( "\nHelpLink: {0}\n", e.HelpLink); } // catch custom exception catch (MyCustomException e) { Console.WriteLine( "\nMyCustomException! Msg: {0}", e.Message); Console.WriteLine( "\nHelpLink: {0}\n", e.HelpLink); } catch // catch any uncaught exceptions ...