The Simplest C# Events Example Imaginable

Introduction

Most examples of events and delegates in C# are more complicated and intimidating than a person new to both C# and OOP would like (VBA made it just too easy on us). While I will not explain the code, it is simple enough that what code to replace in a copy-paste is clear. I have created what I think may be one of the simplest examples of Event Handling in C#. A Metronome class creates events at a tick of 3 seconds, and a Listener class hears the metronome ticks and prints "HEARD IT" to the console every time it receives an event. This should give the novice programmer a clear idea what is necessary to generate and pass events. Plop the following code right into a class file in a blank C# project.

using System;
namespace wildert
{
    public class Metronome
    {
        public event TickHandler Tick;
        public EventArgs e = null;
        public delegate void TickHandler(Metronome m, EventArgs e);
        public void Start()
        {
            while (true)
            {
                System.Threading.Thread.Sleep(3000);
                if (Tick != null)
                {
                    Tick(this, e);
                }
            }
        }
    }
        public class Listener
        {
            public void Subscribe(Metronome m)
            {
                m.Tick += new Metronome.TickHandler(HeardIt);
            }
            private void HeardIt(Metronome m, EventArgs e)
            {
                System.Console.WriteLine("HEARD IT");
            }

        }
    class Test
    {
        static void Main()
        {
            Metronome m = new Metronome();
            Listener l = new Listener();
            l.Subscribe(m);
            m.Start();
        }
    }
}

A slightly more complicated example is if the event has information passed with it, such as mouse coordinates for a mouse event or which key is pressed for a keypress event. To do this you need to create an appropriate class derived from the EventArgs class and then set an instance of it before raising the event. See below:

using System;
namespace wildert
{
    
    public class TimeOfTick : EventArgs
    {
        private DateTime TimeNow;
        public DateTime Time
        {
            set
            {
                TimeNow = value;
            }
            get
            {
                return this.TimeNow;
            }
        }
    }
    public class Metronome
    {
        public event TickHandler Tick;
        public delegate void TickHandler(Metronome m, TimeOfTick e);
        public void Start()
        {
            while (true)
            {
                System.Threading.Thread.Sleep(3000);
                if (Tick != null)
                {
                    TimeOfTick TOT = new TimeOfTick();
                    TOT.Time = DateTime.Now;
                    Tick(this, TOT);
                }
            }
        }
    }
        public class Listener
        {
            public void Subscribe(Metronome m)
            {
                m.Tick += new Metronome.TickHandler(HeardIt);
            }
            private void HeardIt(Metronome m, TimeOfTick e)
            {
                System.Console.WriteLine("HEARD IT AT {0}",e.Time);
            }

        }
    class Test
    {
        static void Main()
        {
            Metronome m = new Metronome();
            Listener l = new Listener();
            l.Subscribe(m);
            m.Start();
        }
    }
}

When you add a button to a form in C# and double click on the button in the form designer, you are taken to a method equivalent to "Heardit", but it will be appropriately named something like Button1_Click. Button1 is set up with a standard event handler (System.EventHandler, which is discussed below in the comments) and its own events (Click, MouseMove, etc). If you dig into the Form1.Designer.cs code, you will find the last necessary bit of code.

this.button1.click += new System.EventHandler(this.button1_Click);

What the auto-designer code did for you was add a new class Button1 with Button events and uses System.EventHandler, and then had Form1 subscribe to its events and create a Button1_Click method in Form1. Awful English, I'm an engineer.