大話設計模式之策略模式(strategy)

策略模式：它定義了算法家族，分別封裝起來，讓他們之間能夠互相替換，此模式讓算法的變化不會影響使用算法的用戶。

針對商城收銀模式，打折，返現促銷等的例子：

打折仍是促銷其實都是一些算法，能夠用工廠模式來生成算法對象，但算法自己只是一種策略，重要的是這些算法隨時均可能替換的，而封裝變化點是咱們面向對象的一種重要的思惟方式，首先來看下策略模式的結構圖和基本代碼：

1）結構圖

2）代碼

strategy類，定義全部支持的方法的公共接口

    public abstract class Strategy
    {
        //算法公告接口
        public abstract void AlgorithmInterface();
    }

View Code

ConcreteStrategy,封裝了具體的方法或行爲，繼承strategy

    public class ConcreteStrategyA : Strategy
    {
        public override void AlgorithmInterface()
        {
            Console.WriteLine("算法A的實現");
        }
    }
    public class ConcreteStrategyB :Strategy
    {
        public override void AlgorithmInterface()
        {
            Console.WriteLine("算法B的實現");
        }
    }

View Code

Context,用一個ConcreteStrategy來配置，維護一個對Strategy對象的引用

    public class Context
    {
        private Strategy strategy;

        public Context(Strategy strategy)
        {
            this.strategy = strategy;
        }

        //上下文接口
        public void ContextInterface()
        {
            strategy.AlgorithmInterface();
        }
    }

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客戶端代碼：

        static void Main(string[] args)
        {
            Context context;

            context = new Context(new ConcreteStrategyA());
            context.ContextInterface();

            context=new Context(new ConcreteStrategyB());
            context.ContextInterface();

            Console.ReadLine();
        }

View Code

用策略模式來實現商場收費：

定義公共接口和各類收費策略

//定義公共收費接口類    
public abstract class CashSuper
    {
        //公共的收費接口
        public abstract double acceptCash(double money); 
    }
//定義各類收費策略
    public class CashNomal:CashSuper
    {
        public override double acceptCash(double money)
        {
            return money;
        }
    }
    public class CashRebate:CashSuper
    {
        private double rebate = 1;
        public CashRebate(string rebate)
        {
            this.rebate = Convert.ToDouble(rebate);
        }

        public override double acceptCash(double money)
        {
            return money * this.rebate;
        }
    }

    public class CashReturn:CashSuper
    {
        public double condition = 0.0d;
        public double returnMoney = 0.0d;

        public CashReturn(string condition, string returnMoney)
        {
            this.returnMoney = Double.Parse(returnMoney);
            this.condition = Double.Parse(condition);
        }
        public override double acceptCash(double money)
        {
            double result = money;
            if(money >= condition)
            {
                result = money - Math.Floor(result/condition)*returnMoney;
            }
            return result;
        }

    }

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定義Context：

    public class CashContext
    {
        private CashSuper cashsuper;
        public CashContext(CashSuper cs)
        {
            cashsuper = cs;
        }
        public double GetResult(double money)
        {
            return cashsuper.acceptCash(money);
        }
    }

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客戶段代碼：

        static void Main(string[] args)
        {
            double totle = 500.0d;
            double result = 0.0d;
            CashContext context;
            context = new CashContext(new CashNomal());
            result =  context.GetResult(totle);
            Console.WriteLine(result);

            context = new CashContext(new CashRebate("0.3"));
            result = context.GetResult(totle);
            Console.WriteLine(result);

            context =new CashContext(new CashReturn("300","50"));
            result = context.GetResult(totle);
            Console.WriteLine(result);

            Console.ReadLine();
        }

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