Csharp/C Sharp/Language Basics/Event Handler

Demonstrate passing an object to an event handler and performing the proper cast in the method

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
 
// ObjEvent.cs -- Demonstrate passing an object to an event handler and
//                performing the proper cast in the method.
//
//                Compile this program with the following command line:
//                    C:>csc ObjEvent.cs
using System;
namespace nsEvents
{
    public class ObjEvent1
    {
        public delegate void EventHandler (object obj);
        public event EventHandler EvInvoke;
        public void FireEvent (object obj)
        {
            if (obj != null)
                EvInvoke (obj);
        }
        static public void Main ()
        {
            ObjEvent1 main = new ObjEvent1 ();
            main.EvInvoke = new ObjEvent1.EventHandler (ObjEvent);
            main.FireEvent (42);
            main.FireEvent (42.0);
        }
        static void ObjEvent (object obj)
        {
            if (obj is double)
            {
                Console.WriteLine ("Received a double object: " + (double) obj);
            }
            else if (obj is int)
            {
                Console.WriteLine ("Received an int object: " + (int) obj);
            }
        }
    }
}

illustrates the use of an event

/*
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;
  }
}

Shows how multiple objects may subscribe to the same event

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
 // Subscrib.cs -- Shows how multiple objects may subscribe to the same
//                event.
//
//                Compile this program with the following command line:
//                    C:>csc Subscrib.cs
using System;
namespace nsEvents
{
    public class Subscrib
    {
        // Declare an instance of the clsDelegate class. The event variable
        // is not static.
        static public clsDelegate dlg = new clsDelegate ();
        static public void Main ()
        {
            // Add clsMain to the event list
            dlg.DoEvent += new clsDelegate.StringHandler (ShowEvent);
            // Create subscribers for the event
            clsSubscriber sub = new clsSubscriber ();
            clsNextSubscriber sub2 = new clsNextSubscriber ();
            // Fire the event.
            dlg.FireEvent ("Fired from Main()");
        }
        static public void ShowEvent (string str)
        {
            Console.WriteLine ("Main handled event: " + str);
        }
    }

    public class clsDelegate
    {
        
        // Declare a delegate for the event
        public delegate void StringHandler (string str);
        
        // A variable to hold the delegate
        public event StringHandler DoEvent;
        
        // This method will trigger the event.
        public void FireEvent (string str)
        {
            if (DoEvent != null)
                DoEvent (str);
        }
    }
    public class clsSubscriber
    {
        public clsSubscriber ()
        {
            Subscrib.dlg.DoEvent +=
                         new clsDelegate.StringHandler (SubscribeEvent);
        }
        public void SubscribeEvent (string str)
        {
            Console.WriteLine ("Subscriber handled event: " + str);
        }
    }
    public class clsNextSubscriber
    {
        public clsNextSubscriber ()
        {
            Subscrib.dlg.DoEvent +=
                         new clsDelegate.StringHandler (SubscribeEvent);
        }
        public void SubscribeEvent (string str)
        {
            Console.WriteLine ("Next Subscriber handled event: " + str);
        }
    }
}