c#如何实现接口事件

namespace ImplementInterfaceEvents 
{ 
 public interface IDrawingObject 
 { 
  event EventHandler ShapeChanged; 
 } 
 public class MyEventArgs : EventArgs
 { 
  // class members 
 } 
 public class Shape : IDrawingObject 
 { 
  public event EventHandler ShapeChanged; 
  void ChangeShape() 
  { 
   // Do something here before the event… 

   OnShapeChanged(new MyEventArgs(/*arguments*/)); 

   // or do something here after the event.
  } 
  protected virtual void OnShapeChanged(MyEventArgs e) 
  { 
   ShapeChanged?.Invoke(this, e); 
  } 
 } 

}

namespace WrapTwoInterfaceEvents
{
 using System;

 public interface IDrawingObject
 {
  // Raise this event before drawing
  // the object.
  event EventHandler OnDraw;
 }
 public interface IShape
 {
  // Raise this event after drawing
  // the shape.
  event EventHandler OnDraw;
 }

 // Base class event publisher inherits two
 // interfaces, each with an OnDraw event
 public class Shape : IDrawingObject, IShape
 {
  // Create an event for each interface event
  event EventHandler PreDrawEvent;
  event EventHandler PostDrawEvent;

  object objectLock = new Object();

  // Explicit interface implementation required.
  // Associate IDrawingObject's event with
  // PreDrawEvent
  #region IDrawingObjectOnDraw
  event EventHandler IDrawingObject.OnDraw
  {
   add
   {
    lock (objectLock)
    {
     PreDrawEvent += value;
    }
   }
   remove
   {
    lock (objectLock)
    {
     PreDrawEvent -= value;
    }
   }
  }
  #endregion
  // Explicit interface implementation required.
  // Associate IShape's event with
  // PostDrawEvent
  event EventHandler IShape.OnDraw
  {
   add
   {
    lock (objectLock)
    {
     PostDrawEvent += value;
    }
   }
   remove
   {
    lock (objectLock)
    {
     PostDrawEvent -= value;
    }
   }
  }

  // For the sake of simplicity this one method
  // implements both interfaces.
  public void Draw()
  {
   // Raise IDrawingObject's event before the object is drawn.
   PreDrawEvent?.Invoke(this, EventArgs.Empty);

   Console.WriteLine("Drawing a shape.");

   // Raise IShape's event after the object is drawn.
   PostDrawEvent?.Invoke(this, EventArgs.Empty);
  }
 }
 public class Subscriber1
 {
  // References the shape object as an IDrawingObject
  public Subscriber1(Shape shape)
  {
   IDrawingObject d = (IDrawingObject)shape;
   d.OnDraw += d_OnDraw;
  }

  void d_OnDraw(object sender, EventArgs e)
  {
   Console.WriteLine("Sub1 receives the IDrawingObject event.");
  }
 }
 // References the shape object as an IShape
 public class Subscriber2
 {
  public Subscriber2(Shape shape)
  {
   IShape d = (IShape)shape;
   d.OnDraw += d_OnDraw;
  }

  void d_OnDraw(object sender, EventArgs e)
  {
   Console.WriteLine("Sub2 receives the IShape event.");
  }
 }

 public class Program
 {
  static void Main(string[] args)
  {
   Shape shape = new Shape();
   Subscriber1 sub = new Subscriber1(shape);
   Subscriber2 sub2 = new Subscriber2(shape);
   shape.Draw();

   // Keep the console window open in debug mode.
   System.Console.WriteLine("Press any key to exit.");
   System.Console.ReadKey();
  }
 }
}
/* Output:
 Sub1 receives the IDrawingObject event.
 Drawing a shape.
 Sub2 receives the IShape event.
*/