All About Events

Let's discuss a little bit more about Events. How are Events different from Delegates?

For events-

• The event keyword is a modifier- to a delegate type, the most frequent being EventHandler for event handling situations.
• The event keyword allows a delegate type to be exposed in an interface.
• Events come with add and remove methods, much like get and set methods for properties.
• Events have a strict method signature (object ok, EventArgs e).

Here is some simple test code demonstrating the use of Events.

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

namespace TestEvents
{

    class TinyMechErrorArgs : EventArgs
    {
        public int MechError { get; set; }

        public TinyMechErrorArgs(int error)
        {
            MechError = error;
        }
    }

    // ----------------------------------------------------------------
    // TinyMech
    //
    // Machine that publishes error events
    //
    // ----------------------------------------------------------------

    class TinyMech
    {
        // EventHandlers must have args (object sender, EventArgs e)
        public event EventHandler ErrorEventHappened;

        public void Run()
        {
            Random r = new Random();
            for(int i=0; i<1000; i++)
            {
                if (r.Next(100)==1)
                {
                    ErrorEventHappened(this, new TinyMechErrorArgs(i));
                }
            }
        }
    }


    // ----------------------------------------------------------------
    // TinyReporter
    //
    // Machine that listens for errors and reports it to main console
    //
    // ----------------------------------------------------------------

    class TinyReporter
    {
        public void ListenToMachine(TinyMech m)
        {
            m.ErrorEventHappened += ReportError;
        }

        private void ReportError(object sender, EventArgs e)
        {
            if (sender is TinyMech)
            {
                TinyMechErrorArgs ea = (TinyMechErrorArgs) e;
                Console.Out.WriteLine("Error on {0}", ea.MechError);
            }
        }
    }


    class Program
    {
        static void Main(string[] args)
        {
            TinyMech m = new TinyMech();
            TinyReporter r = new TinyReporter();
            r.ListenToMachine(m);
            m.Run();
            Console.In.ReadLine();
        }
    }
}