CustomExceptions.cs

using System;
using System.IO;
using System.Runtime.CompilerServices;
using System.Runtime.Serialization;

/* Custom Exception Notes
 * 
 * End the custom exception class name with 'Exception'. All .NET exceptions end with the 'Exception' suffix. eg. UserAlreadyLoggedInException
 * 
 * If you want to provide the capability to use innerExceptions, you must overload the constructor as seen below.
 * 
 * If you want your Exception class object to work across application domains, then the object must be serializable. To make your exception class serializable, mark
 * it with the [Serializable] attribute and provide a constructor that invokes the base Exception class constructor that takes in SerializationInfo and StreamingContext
 * objects as parameters
 * 
 * Program Requirements (to demonstrate creating a custom Exception class)
 *  1. The application should allow the user to have only one logged in session
 *  2. If the user is already logged in, and the user opens another browser window to try to log in again
 *     the application should throw an error stating that he/she is already logged in, in another browser window/tab
 * 
 */

class Program
{
    public static void Main()
    {
        try
        {
            throw new UserAlreadyLoggedInException("You are already logged in.");
        }
        catch (UserAlreadyLoggedInException ex)
        {
            Console.WriteLine(ex.Message);
        }
        
        Console.ReadKey();
    }        
}

[Serializable]
public class UserAlreadyLoggedInException : Exception
{
    public UserAlreadyLoggedInException() //parameterless constructor, inheriting from Exception base class
        : base()
    {
    }

    public UserAlreadyLoggedInException(string message) //method overload that accepts a string
        : base(message) 
    {
    }

    public UserAlreadyLoggedInException(string message, Exception innerException) //method overload that can accept a string and track an inner exception
        : base(message, innerException)
    {
    }

    public UserAlreadyLoggedInException(SerializationInfo info, StreamingContext context) //constructor that supports base class serialization
        : base(info, context)
    {
    }
}