命令模式（Command Pattern）

命令模式（Command Pattern）是一种对象行为模式，分离了接受请求的对象与实现处理请求工作的对象，在软件系统中，“行为请求者”与“行为实现者”通常呈现一种“紧耦合”。但在某些场合，比如要对行为进行“记录、撤销/重做、事务”等处理，这种无法抵御变化的紧耦合是不合适的。在这种情况下，将一组行为抽象为对象，实现二者之间的松耦合。这样，已经存在的类可以保持不变，使得增加新类的工作更简单。例如，很多软件的宏命令就提高了系统的自动化程度。命令模式还可以分离用户界面和业务对象，降低系统的耦合度。

using System;
using System.Collections;
using System.Collections.Generic;

namespace ConsoleApplication
{

    //一般每个接口或类都写在单独的.cs文件中
    //本示例为了执行查看方便才写在一起  
    public interface IGraphCommand
    {
        void Draw();
        void Undo();
    }
    public struct Point
    {
        public Point(int x, int y)
        {
            this.X = x;
            this.Y = y;
        }
        public int X { get; set; }
        public int Y { get; set; }
    }

    public class Line : IGraphCommand
    {
        private Point startPoint;
        private Point endPoint;
        public Line(Point start, Point end)
        {
            startPoint = start;
            endPoint = end;
        }
        public void Draw()
        {
            Console.WriteLine("Draw Line:{0} To {1}", startPoint.ToString(), endPoint.ToString());
        }
        public void Undo()
        {
            Console.WriteLine("Erase Line:{0} To {1}", startPoint.ToString(), endPoint.ToString());
        }
    }
    public class Rectangle : IGraphCommand
    {
        private Point topLeftPoint;
        private Point bottomRightPoint;
        public Rectangle(Point topLeft, Point bottomRight)
        {
            topLeftPoint = topLeft; bottomRightPoint = bottomRight;
        }
        public void Draw()
        {
            Console.WriteLine("Draw Rectangle: Top Left Point {0},  Bottom Right Point {1}", topLeftPoint.ToString(), bottomRightPoint.ToString());
        }
        public void Undo()
        {
            Console.WriteLine("Erase Rectangle: Top Left Point {0},  Bottom Right Point {1}", topLeftPoint.ToString(), bottomRightPoint.ToString());
        }
    }
    public class Circle : IGraphCommand
    {
        private Point centerPoint;
        private int radius;
        public Circle(Point center, int radius)
        {
            centerPoint = center;
            this.radius = radius;
        }
        public void Draw()
        {
            Console.WriteLine("Draw Circle: Center Point {0},  Radius {1}", centerPoint.ToString(), radius.ToString());
        }
        public void Undo()
        {
            Console.WriteLine("Erase Circle: Center Point {0},  Radius {1}", centerPoint.ToString(), radius.ToString());
        }
    }

    public class Graphics
    {
        Stack<IGraphCommand> commands = new Stack<IGraphCommand>();
        public void Draw(IGraphCommand command)
        {
            command.Draw();
            commands.Push(command);
        }
        public void Undo()
        {
            IGraphCommand command = commands.Pop();
            command.Undo();
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Line line = new Line(new Point(10, 10), new Point(100, 10));
            Rectangle rectangle = new Rectangle(new Point(20, 20), new Point(60, 30));
            Circle circle = new Circle(new Point(600, 600), 200);

            Graphics graphics = new Graphics();
            graphics.Draw(line);
            graphics.Draw(rectangle);
            graphics.Undo();
            graphics.Draw(circle);

            Console.ReadKey();
        }
    }
}