illustrates the use of an event : Event Handler : Language Basics C# Source Code

    

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy

Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example12_4.cs illustrates the use of an event
*/

using System;


// declare the MeltdownEventArgs class (implements EventArgs)
class MeltdownEventArgs : EventArgs
{

  // declare a private field named message
  private string message;

  // define a constructor
  public MeltdownEventArgs(string message)
  {
    this.message = message;
  }

  // define a property to get the message
  public string Message
  {
    get
    {
      return message;
    }
  }

}


// declare the Reactor class
class Reactor
{

  // declare a private field named temperature
  private int temperature;

  // declare a delegate class named MeltdownHandler
  public delegate void MeltdownHandler(
    object reactor,
    MeltdownEventArgs myMEA
  );

  // declare an event named OnMeltdown
  public event MeltdownHandler OnMeltdown;

  // define a property to set the temperature
  public int Temperature
  {
    set
    {
      temperature = value;

      // if the temperature is too high, the reactor melts down
      if (temperature > 1000)
      {
        MeltdownEventArgs myMEA =
          new MeltdownEventArgs("Reactor meltdown in progress!");
          OnMeltdown(this, myMEA);
      }
    }
  }

}


// declare the ReactorMonitor class
class ReactorMonitor
{

  // define a constructor
  public ReactorMonitor(Reactor myReactor)
  {
    myReactor.OnMeltdown +=
      new Reactor.MeltdownHandler(DisplayMessage);
  }

  // define the DisplayMessage() method
  public void DisplayMessage(
    object myReactor, MeltdownEventArgs myMEA
  )
  {
    Console.WriteLine(myMEA.Message);
  }

}


public class Example12_4
{

  public static void Main()
  {

    // create a Reactor object
    Reactor myReactor = new Reactor();

    // create a ReactorMonitor object
    ReactorMonitor myReactorMonitor = new ReactorMonitor(myReactor);

    // set myReactor.Temperature to 100 degrees Centigrade
    Console.WriteLine("Setting reactor temperature to 100 degrees Centigrade");
    myReactor.Temperature = 100;

    // set myReactor.Temperature to 500 degrees Centigrade
    Console.WriteLine("Setting reactor temperature to 500 degrees Centigrade");
    myReactor.Temperature = 500;

    // set myReactor.Temperature to 2000 degrees Centigrade
    // (this causes the reactor to meltdown)
    Console.WriteLine("Setting reactor temperature to 2000 degrees Centigrade");
    myReactor.Temperature = 2000;

  }

}