c#接口事件如何实现

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.
*/