装饰者模式

四人组之装饰者模式。

1、例子：饮料和调料包之间的计价功能等实现。

2.实质上：相同接口，实现功能的不断扩充。

3.优美的一句话：“代码应如晚霞中池中莲花一样关闭（免于改变），又如晨曦中此花一样绽放（功能扩展）”。不修改代码的情况下进行扩展

4.实质上：装饰者可以在被装饰者行为之前(后)加上自己的行为，

为什么装饰者和被装饰者继承同一个baseclass ？

为了和被装饰者在类型匹配的基础上达到新的行为

实现：

   static void Main(string[] args)
    {
        Coffee myCoffee = new Coffee(10);//一个被装饰者对象

        DecoratorBase myDecorate = new DecoratorSugar(myCoffee, 0.1);//创建装饰者
        myDecorate = new DecoratorSugar(myDecorate, 0.1);//双糖
        myDecorate = new DecoratorMilk(myDecorate, 0.3);

        Console.WriteLine("price:" + myDecorate.GetCost());
        Console.WriteLine("describe:" + myDecorate.GetDescribe());
    }

    /// <summary>
    /// 饮料相关基类：装饰者和被装饰者
    /// </summary>
    class Drink
    {
        protected string mDescribe = string.Empty;
        protected double mCost = 0.0;

        public Drink()
        {
            mDescribe = "--BaseDrink--";
        }

        public virtual string GetDescribe()
        {
            return mDescribe;
        }
        public virtual double GetCost()
        {
            return mCost;
        }
    }

    /// <summary>
    /// 被装饰者：咖啡
    /// </summary>
    class Coffee : Drink
    {
        public Coffee(double price)
        {
            mDescribe = "--Coffee--";
            mCost = price;
        }
    }
    /// <summary>
    /// 被装饰者：果汁
    /// </summary>
    class Juice : Drink
    {
        public Juice(double price)
        {
            mCost = price;
        }
    }

    /// <summary>
    /// 装饰者
    /// </summary>
    class DecoratorBase : Drink
    {
        protected Drink mDrink = null;

        public DecoratorBase(Drink drink, double price)
        {
            mDrink = drink;

            mCost = price;
            mDescribe = "--decorate--";
        }
    }

    class DecoratorSugar : DecoratorBase
    {
        public DecoratorSugar(Drink drink, double price)
            : base(drink, price)
        {
            mDescribe = "--sugar--";
        }

        public override string GetDescribe()
        {
            return mDescribe + mDrink.GetDescribe();
        }

        public override double GetCost()
        {
            return mCost + mDrink.GetCost();
        }

    }

    class DecoratorMilk : DecoratorBase
    {
        public DecoratorMilk(Drink drink, double price)
            : base(drink, price)
        {
            mDescribe = "--Milk--";
        }
        public override string GetDescribe()
        {
            return mDescribe + mDrink.GetDescribe();
        }

        public override double GetCost()
        {
            return mCost + mDrink.GetCost();
        }
    }

结果：

添加功能：我们需要给每个饮料设置 小、中、大杯和不同价格，对应的调料包的需要小中大和不同价格。

调料的大中小不是自己决定的，而是由饮料决定的。

   static void Main(string[] args)
    {
        Coffee myCoffee = new Coffee(10, SizeType.Min);//一个被装饰者对象

        DecoratorBase myDecorate = new DecoratorSugar(myCoffee, 0.1);//创建装饰者
        myDecorate = new DecoratorSugar(myDecorate, 0.1);//双糖
        myDecorate = new DecoratorMilk(myDecorate, 0.3);

        Console.WriteLine("price:" + myDecorate.GetCost());
        Console.WriteLine("describe:" + myDecorate.GetDescribe());
    }

    enum SizeType
    {
        Max = 1,
        Mid = 2,
        Min = 3,
    }

    public static double[] percentPrice = { 1, 0.8, 0.5 };//每个调料包size价格百分比

    /// <summary>
    /// 饮料相关基类：装饰者和被装饰者
    /// </summary>
    class Drink
    {
        protected string mDescribe = string.Empty;
        protected double mCost = 0.0;
        protected SizeType mSizeType = SizeType.Max;

        public Drink()
        {
            mDescribe = "--BaseDrink--";
        }

        public virtual string GetDescribe()
        {
            return mDescribe;
        }
        public virtual double GetCost()
        {
            return mCost;
        }

        public SizeType GetSize()
        {
            return mSizeType;
        }
    }

    /// <summary>
    /// 被装饰者：咖啡
    /// </summary>
    class Coffee : Drink
    {
        public Coffee(double price, SizeType sizeType)
        {
            mDescribe = "--Coffee--";
            mCost = price;
            mSizeType = sizeType;
        }
    }
    /// <summary>
    /// 被装饰者：果汁
    /// </summary>
    class Juice : Drink
    {
        public Juice(double price, SizeType sizeType)
        {
            mDescribe = "--Juice--";
            mCost = price;
            mSizeType = sizeType;
        }
    }

    /// <summary>
    /// 装饰者
    /// </summary>
    class DecoratorBase : Drink
    {
        protected Drink mDrink = null;

        public DecoratorBase(Drink drink, double price)
        {
            if (drink != null)
            {
                mDrink = drink;

                mCost = price;
                mDescribe = "--decorate--";

                mSizeType = mDrink.GetSize();
            }
        }
    }

    class DecoratorSugar : DecoratorBase
    {
        public DecoratorSugar(Drink drink, double price)
            : base(drink, price)
        {
            mDescribe = "--sugar--";
        }

        public override string GetDescribe()
        {
            return mDescribe + mDrink.GetDescribe();
        }

        public override double GetCost()
        {
            double percent = percentPrice[(int)mSizeType - 1];
            return mCost * percent + mDrink.GetCost();
        }

    }

    class DecoratorMilk : DecoratorBase
    {
        public DecoratorMilk(Drink drink, double price)
            : base(drink, price)
        {
            mDescribe = "--Milk--";
        }
        public override string GetDescribe()
        {
            return mDescribe + mDrink.GetDescribe();
        }

        public override double GetCost()
        {
            double percent = percentPrice[(int)mSizeType - 1];
            return mCost * percent + mDrink.GetCost();
        }
    }