//Demo1:Declaring an event in an interface and implementing it in //a class.

// event_keyword.cs

using System;

public delegate void MyDelegate();   // delegate declaration

public interface I

{

   event MyDelegate MyEvent;

   void FireAway();

}

public class MyClass: I

{

   public event MyDelegate MyEvent;

   public void FireAway()

   {

      if (MyEvent != null)

         MyEvent();

   }

}

public class MainClass

{

   static private void f()

   {

      Console.WriteLine("This is called when the event fires.");

   }

   static public void Main ()

   {

      I i = new MyClass();

      i.MyEvent += new MyDelegate(f);

      i.FireAway();

   }

}

//Demo2:One use for accessor-declarations is to expose a large //number of events without allocating a field for each event, but //instead using a hash table to store the event instances. This is //only useful if you have a very large number of events, but you //expect most of the events will not be implemented.

// event_keyword2.cs

using System;

using System.Collections;

public delegate void MyDelegate1(int i);

public delegate void MyDelegate2(string s);

public delegate void MyDelegate3(int i, object o);

public delegate void MyDelegate4();

public class PropertyEventsSample

{

   private Hashtable eventTable = new Hashtable();

   public event MyDelegate1 Event1

   {

      add

      {

         eventTable["Event1"] = (MyDelegate1)eventTable["Event1"] + value;

      }

      remove

      {

         eventTable["Event1"] = (MyDelegate1)eventTable["Event1"] - value;

      }

   }

   public event MyDelegate1 Event2

   {

      add

      {

         eventTable["Event2"] = (MyDelegate1)eventTable["Event2"] + value;

      }

      remove

      {

         eventTable["Event2"] = (MyDelegate1)eventTable["Event2"] - value;

      }

   }

   public event MyDelegate2 Event3

   {

      add

      {

         eventTable["Event3"] = (MyDelegate2)eventTable["Event3"] + value;

      }

      remove

      {

         eventTable["Event3"] = (MyDelegate2)eventTable["Event3"] - value;

      }

   }

   public event MyDelegate3 Event4

   {

      add

      {

         eventTable["Event4"] = (MyDelegate3)eventTable["Event4"] + value;

      }

      remove

      {

         eventTable["Event4"] = (MyDelegate3)eventTable["Event4"] - value;

      }

   }

   public event MyDelegate3 Event5

   {

      add

      {

         eventTable["Event5"] = (MyDelegate3)eventTable["Event5"] + value;

      }

      remove

      {

         eventTable["Event5"] = (MyDelegate3)eventTable["Event5"] - value;

      }

   }

   public event MyDelegate4 Event6

   {

      add

      {

         eventTable["Event6"] = (MyDelegate4)eventTable["Event6"] + value;

      }

      remove

      {

         eventTable["Event6"] = (MyDelegate4)eventTable["Event6"] - value;

      }

   }

}

public class MyClass

{

   public static void Main()

   {

   }

}

//Deom3

public class SampleEventArgs

    {

        public SampleEventArgs(string s) { Text = s; }

        public String Text {get; private set;} // readonly

    }

    public class Publisher

    {

        // Declare the delegate (if using non-generic pattern).

        public delegate void SampleEventHandler(object sender, SampleEventArgs e);

        // Declare the event.

        public event SampleEventHandler SampleEvent;

        // Wrap the event in a protected virtual method

        // to enable derived classes to raise the event.

        protected virtual void RaiseSampleEvent()

        {

            // Raise the event by using the () operator.

            if (SampleEvent != null)

                SampleEvent(this, new SampleEventArgs("Hello"));

        }

    }