C#:实现接口中定义的事件

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
event EventHandler IDrawingObject.OnDraw
{
add
{
lock (objectLock)
{
PreDrawEvent += value;
}
}
remove
{
lock (objectLock)
{
PreDrawEvent -= value;
}
}
}
// 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.
EventHandler handler = PreDrawEvent;
if (handler != null)
{
handler(this, new EventArgs());
}
Console.WriteLine("Drawing a shape.");

// RaiseIShape's event after the object is drawn.
handler = PostDrawEvent;
if (handler != null)
{
handler(this, new EventArgs());
}
}
}
public class Subscriber1
{
// References the shape object as an IDrawingObject
public Subscriber1(Shape shape)
{
IDrawingObject d = (IDrawingObject)shape;
d.OnDraw += new EventHandler(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 += new EventHandler(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.
*/