ch5_4.cs

《c#技术内幕代码》

using System;

public class EventTestClass
{
     // The value to track
     private int nValue;
     
     // Allow a handler for the event
     public delegate void ValueChangedEventHandler();
     
     // This is the event itself
     public event ValueChangedEventHandler Changed;

     // This method is used to fire the event     
     protected virtual void OnChanged() 
     {
        if (Changed != null)
           Changed();
	else
	    Console.WriteLine("Event fired. No handler!");
	
     }
     
     public EventTestClass(int nValue)
     {
        SetValue( nValue );
     }
     public void SetValue( int nV )
     {
        if ( nValue != nV )
	{
            nValue = nV;
	    // Fire the event
	    OnChanged();
	}
     }
}

public class CH5_4
{
   public void HandleChange1()
   {
      Console.WriteLine("Handler 1 Called");
   }
   public void HandleChange2()
   {
      Console.WriteLine("Handler 2 Called");
   }
   public CH5_4()
   {
   }
   
   public static void Main()
   {
      EventTestClass etc = new EventTestClass(3);
      CH5_4 app = new CH5_4();
      
      // Create a handler for this class
      etc.Changed += new EventTestClass.ValueChangedEventHandler(app.HandleChange1);
      etc.Changed += new EventTestClass.ValueChangedEventHandler(app.HandleChange2);
      
      etc.SetValue(5);
      etc.SetValue(5);
      etc.SetValue(3);
   }
}