Learning C# 3.0

Custom Exceptions

The intrinsic exception types C# 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.

Sometimes, however, you will 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. Even though you’ll rarely need to do it, Example 16-7 illustrates the creation of a custom exception.

Example 16-7. Although C# provides a range of exceptions that you’ll use most of the time, you can define a custom exception if you need it

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Example_16_7_ _ _ _Custom_Exception
{
    // custom exception class
    public class MyCustomException : System.Exception
    {
        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); ...