装饰模式

一，概念

摘自TerryLee的博客（http://terrylee.cnblogs.com/archive/2006/03/01/340592.html）

概述

在软件系统中，有时候我们会使用继承来扩展对象的功能，但是由于继承为类型引入的静态特质，使得这种扩展方式缺乏灵活性；并且随着子类的增多（扩展功能的增多），各种子类的组合（扩展功能的组合）会导致更多子类的膨胀。如何使“对象功能的扩展”能够根据需要来动态地实现？同时避免“扩展功能的增多”带来的子类膨胀问题？从而使得任何“功能扩展变化”所导致的影响将为最低？这就是本文要讲的Decorator模式。

意图

动态地给一个对象添加一些额外的职责。就增加功能来说，Decorator模式相比生成子类更为灵活。[GOF 《设计模式》]

二，实现 

using System;
using System.Collections.Generic;
using System.Text;
using DebugOut = System.Diagnostics.Debug;

namespace CsharpBase.DesignPattern
{
    /// <summary>
    /// 装饰模式
    /// </summary>
    class DecoratorDemo
    {
        public static void Run()
        {
            Dark dark = new GreenDark();
            //能飞的鸭子
            FlyDarkWapper flyWapper = new FlyDarkWapper(dark);
            //能飞，也能唱歌的鸭子
            SingDarkWapper singWrapper = new SingDarkWapper(flyWapper);
            //能飞，能唱歌，还能跳舞的鸭子
            DanceDarkWapper danceWrapper = new DanceDarkWapper(singWrapper);
            danceWrapper.Action();

            //结果
            //i'm a Green dark
            //now,i can fly.
            //now i can sing
            //now,i can dance
        }
    }

    public abstract class Dark
    { 
       public abstract void Action();
    }

    public class RedDark : Dark
    {
        public override void Action()
        {
            DebugOut.WriteLine("i'm a red dark");            
        }
    }

    public class GreenDark : Dark
    {
        public override void Action()
        {
            DebugOut.WriteLine("i'm a Green dark");
        }
    }

    public abstract class DarkWapper : Dark
    {
        Dark dark;
        public DarkWapper(Dark dark)
        {
            this.dark = dark;
        }
        public override void Action()
        {
            dark.Action();
        }
    }

    /// <summary>
    /// 功能扩展（飞）
    /// </summary>
    public class FlyDarkWapper : DarkWapper
    {
        public FlyDarkWapper(Dark dark)
            : base(dark)
        {
        }

        public override void Action()
        {
            base.Action();
            Fly();
        }

        private void Fly()
        {
            DebugOut.WriteLine("now,i can fly.");
        }
    }

    /// <summary>
    /// 功能扩展（唱歌）
    /// </summary>
    public class SingDarkWapper : DarkWapper
    {
        public SingDarkWapper(Dark dark)
            : base(dark)
        {
        }

        public override void Action()
        {
            base.Action();
            Sing();
        }

        private void Sing()
        {
            DebugOut.WriteLine("now i can sing");
        }
    }

    /// <summary>
    /// 功能扩展（跳舞）
    /// </summary>
    public class DanceDarkWapper : DarkWapper
    {
        public DanceDarkWapper(Dark dark)
            : base(dark)
        {
        }

        public override void Action()
        {
            base.Action();
            Dance();
        }

        private void Dance()
        {
            DebugOut.WriteLine("now,i can dance");
        }
    }
}