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The Simplest C# Events Example Imaginable

, 5 Sep 2005 485.4K 127
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A simple metronome example where a class creates events and another receives them.

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.

License

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About the Author

Todd Wilder
Web Developer
United States United States
No Biography provided

Comments and Discussions

 
QuestionThanks so much! Pin
GIANGPZO13-Apr-15 17:10
professionalGIANGPZO13-Apr-15 17:10 
QuestionGreat Help Pin
Member 1098685912-Feb-15 18:37
memberMember 1098685912-Feb-15 18:37 
GeneralMy vote of 5 Pin
Ross Harrison113-Nov-14 7:22
memberRoss Harrison113-Nov-14 7:22 
GeneralMy vote of 1 Pin
maurices500011-Nov-14 9:49
membermaurices500011-Nov-14 9:49 
QuestionFinnally!! Pin
Member 109398703-Sep-14 14:39
memberMember 109398703-Sep-14 14:39 
QuestionNot explained simple Pin
Raja Chandrasekaran5-Jun-14 16:32
memberRaja Chandrasekaran5-Jun-14 16:32 
GeneralMy vote of 1 Pin
Mikant11-Apr-14 14:57
memberMikant11-Apr-14 14:57 
Questionso nice Pin
Member 1058756019-Feb-14 18:19
memberMember 1058756019-Feb-14 18:19 
AnswerRe: so nice Pin
Member 1098685912-Feb-15 19:16
memberMember 1098685912-Feb-15 19:16 
GeneralMy Vote of 5 Pin
jardousman29-Dec-13 1:24
memberjardousman29-Dec-13 1:24 
QuestionAwesome Pin
tm7017014-Dec-13 8:01
membertm7017014-Dec-13 8:01 
GeneralNote quite as simple as it could be Pin
Timok1A5-Aug-13 23:09
memberTimok1A5-Aug-13 23:09 
SuggestionRe: Note quite as simple as it could be [modified] Pin
WiiMaxx12-Dec-13 23:40
memberWiiMaxx12-Dec-13 23:40 
GeneralMy vote of 5 Pin
dano2k310-Jun-13 15:05
memberdano2k310-Jun-13 15:05 
GeneralMy vote of 5 Pin
Heaven202018-Mar-13 11:00
memberHeaven202018-Mar-13 11:00 
GeneralMy vote of 4 Pin
dhiraj226-Feb-13 18:26
memberdhiraj226-Feb-13 18:26 
GeneralMy vote of 5 Pin
Minghang21-Feb-13 20:31
memberMinghang21-Feb-13 20:31 
QuestionBest example on Web Pin
Bit_Flipper10-Jan-13 1:59
memberBit_Flipper10-Jan-13 1:59 
GeneralMy vote of 5 Pin
FranckyVercruysse2-Dec-12 8:12
memberFranckyVercruysse2-Dec-12 8:12 
GeneralExcellent Pin
Member 82577408-Nov-12 10:56
memberMember 82577408-Nov-12 10:56 
QuestionVery Helpful! Pin
bentvisi0n26-Oct-12 10:56
memberbentvisi0n26-Oct-12 10:56 
GeneralMy vote of 5 Pin
Sunny112224-Oct-12 22:12
memberSunny112224-Oct-12 22:12 
QuestionWhy event and Eventargs? [modified] Pin
helpulearn.net28-Sep-12 17:01
memberhelpulearn.net28-Sep-12 17:01 
SuggestionGood, but still a bit complicated for beginner... Pin
Member 471378521-Sep-12 23:38
memberMember 471378521-Sep-12 23:38 
GeneralMy vote of 5 Pin
karthikin6-Aug-12 0:25
memberkarthikin6-Aug-12 0:25 
SuggestionSugestion Pin
TheJediMaster4-Aug-12 9:07
memberTheJediMaster4-Aug-12 9:07 
QuestionI am getting error in below code Pin
mahesh.b.p.c25-Jul-12 19:15
membermahesh.b.p.c25-Jul-12 19:15 
AnswerRe: I am getting error in below code Pin
Todd Wilder25-Jul-12 19:36
memberTodd Wilder25-Jul-12 19:36 
Questionthanks Pin
afueo25-Jun-12 1:40
memberafueo25-Jun-12 1:40 
Question~6.5 years on and it's still helping people Pin
Bit55529-May-12 11:51
memberBit55529-May-12 11:51 
AnswerRe: ~6.5 years on and it's still helping people Pin
Aleholder28-Sep-12 9:50
memberAleholder28-Sep-12 9:50 
Questionvery good article Pin
marek kaszycki21-Feb-12 8:57
membermarek kaszycki21-Feb-12 8:57 
QuestionDelegates and Events Pin
Member 86182067-Feb-12 20:04
memberMember 86182067-Feb-12 20:04 
GeneralMy vote of 5 Pin
George Dawes16-Jan-12 22:15
memberGeorge Dawes16-Jan-12 22:15 
Rantsuggestion for easier reading Pin
taleofsixstrings18-May-11 6:47
membertaleofsixstrings18-May-11 6:47 
GeneralGreat Article Buddy....... Pin
PratapDessai17-Feb-10 19:33
memberPratapDessai17-Feb-10 19:33 
GeneralRe: Great Article Buddy....... Pin
Matic Marko6-Apr-10 21:22
memberMatic Marko6-Apr-10 21:22 
QuestionIs there code for a complete project? Pin
John Chaffins16-Dec-09 10:32
memberJohn Chaffins16-Dec-09 10:32 
AnswerRe: Is there code for a complete project? Pin
Todd Wilder16-Dec-09 11:07
memberTodd Wilder16-Dec-09 11:07 
GeneralRe: Is there code for a complete project? Pin
John Chaffins22-Dec-09 10:42
memberJohn Chaffins22-Dec-09 10:42 
GeneralPublish/Subscribe across user controls Pin
Kjartan933-Sep-09 7:38
memberKjartan933-Sep-09 7:38 
GeneralRe: Publish/Subscribe across user controls Pin
Todd Wilder3-Sep-09 8:45
memberTodd Wilder3-Sep-09 8:45 
QuestionWhat is the reason to check if the event is null? Pin
Maxi Ng @ TW21-Jul-09 21:25
memberMaxi Ng @ TW21-Jul-09 21:25 
AnswerRe: What is the reason to check if the event is null? Pin
Todd Wilder22-Jul-09 12:38
memberTodd Wilder22-Jul-09 12:38 
GeneralThanks! Pin
Gordopolis3-Sep-07 5:58
memberGordopolis3-Sep-07 5:58 
GeneralAn excellent understandable article! Pin
thunderbirdje23-Aug-06 12:39
memberthunderbirdje23-Aug-06 12:39 
GeneralPerfect Pin
snorkie9-Jun-06 10:33
membersnorkie9-Jun-06 10:33 
QuestionSimplified? Pin
Peter Ritchie13-Sep-05 3:12
memberPeter Ritchie13-Sep-05 3:12 
GeneralSimplified Even Further... Pin
Timpie9-Sep-05 12:30
sussTimpie9-Sep-05 12:30 
GeneralMore so... Pin
Pinhead_Me7-Aug-06 7:07
memberPinhead_Me7-Aug-06 7:07 

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