how to use the eventhandler

today when i saw the code about our project,i discover the EventHandler delegate.it’s so fun.we can define a customer class who inherits from EventArgs,we can do somethings about change the value in this class.then we declare an event of delegate type EventHandler of my customer class,when my value changed will send an event message,if somewhere accept the message,will call the function that’s registed to the event.
there is a quesion why my class should inherits from EventArgs?
because delegate type EventHandler has two params(object, EventArgs),we must send an EventArgs param.
1.define a class who inherits from EventArg
2.declare an event
3.regist an event
4.trriger the event when our value changed

using System;
using System.Collections.Generic;
public class  : EventArgs
{
    private string msg;
    public ( string messageData ) {
        msg = messageData;
    }
    public string Message { 
        get { return msg; } 
        set { msg = value; }
    }
}
public class HasEvent
{
// MyEventArgs.
    public event EventHandler<MyEventArgs> SampleEvent;
    public void DemoEvent(string val)
    {
    // Copy to a temporary variable to be thread-safe.
        EventHandler<MyEventArgs> temp = SampleEvent;
        if (temp != null)
            temp(this, new MyEventArgs(val));
    }
}
public class Sample
{
    public static void Main()
    {
        //declare event
        HasEvent he = new HasEvent();
        //regist event
        he.SampleEvent += 
                   new EventHandler<MyEventArgs>(SampleEventHandler);
        //value change trriger event
        he.DemoEvent("Hey there, Bruce!");
        he.DemoEvent("How are you today?");
        he.DemoEvent("I'm pretty good.");
        he.DemoEvent("Thanks for asking!");
    }
    //this function is registed 
    private static void SampleEventHandler(object src, MyEventArgs mea)
    {
        Console.WriteLine(mea.Message);
    }
}

how to use the eventhandler

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