装饰者模式（C#）实现

      我喜欢户外，然后常常去逛户外装备的店子，一般买了自行车等大件，再买登山包，登山鞋等配件就会有优惠。比如买了辆Giant的车，然后买个bag就有优惠，本案例将配件作为装饰者，简单的实现装饰者模式，对于继承，多态掌握的还是很迷惑。有错误还请各位看官帮忙指出，仪器共同进步！

首先定义一个超类Buybike

 public abstract class Buybike
    {
        protected string description="To Get a Bike";
        public virtual string getDescription()
        {
            return description;
        }
        public abstract string Cost();
    }

超类下面定义一个装饰者超类OtherDecorator（所有装饰者【案例中配件】的父类）

public abstract class OtherDecorator:Buybike
    {
        //只是为了将装饰者全部置于其下，无具体实现方法
    }

下面是两个被装饰的类Giant Merida（捷安特，美利达）

class Merida:Buybike
    {
        public Merida()
        {
            description = "Merida";
        }
        public override string Cost()
        {
            return "2000RMB";
        }
    }
public class Giant : Buybike
    {
        public Giant()
        {
            description = "Giant";
        }
        public override string Cost()
        {
            return "3000RMB";
        }

    }

接下去是所有装饰者（配件），全部继承自OtherDecorator

class AddShirt:OtherDecorator
    {
        private  Buybike buyBike;
        public AddShirt(Buybike buyBike)
        {
            this.buyBike = buyBike;
        }
        public override string getDescription()
        {
            return buyBike.getDescription() + "Add a shirt";
        }

        public override string Cost()
        {
            return buyBike.Cost() + "shirt's money:600RMB";
        }
    }
class AddShoes:OtherDecorator
    {
        private  Buybike buyBike;
        public AddShoes(Buybike buyBike)
        {
            this.buyBike = buyBike;
        }
        
        public override string getDescription()
        {
            return buyBike.getDescription() + "Add a shoes";
        }

        public override string Cost()
        {
            return buyBike.Cost() + "shoe's money:300RMB";
        }
    }
class AddBag:OtherDecorator
    {
        private  Buybike buyBike;
        public AddBag(Buybike buyBike)
        {
            this.buyBike = buyBike;
        }
        public override string getDescription()
        {
            return buyBike.getDescription() + "Add a bag";
        }

        public override string Cost()
        {
            return buyBike.Cost() + "bag's money:200RMB";
        }
	}	

程序运行如下：

    class Program
    {
        static void Main(string[] args)
        {
            Buybike a= new Giant();
            a = new AddBag(a);
            a = new AddShirt(a);
            Console.WriteLine(a.Cost());
            Console.WriteLine(a.getDescription());
        }
    }

此模式好处：装饰者和被装饰者从相同基类派生，类型之间的转化非常方便，适合多态的实现。

具体到例子，此处的a具体到是一个基类变量，把它指到下面的子类不必进行类型转化，而且a具体是什么类型，得在运行时才能确定，程序耦合度大大降低。