鴨子應用--策略模式

策略模式定義了算法族，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獨立於使用算法的客戶。

    abstract class Strategy
    {
        // Methods
        abstract public void AlgorithmInterface();
    }

    // "ConcreteStrategyA"
    class ConcreteStrategyA : Strategy
    {
        // Methods
        override public void AlgorithmInterface()
        {
            Console.WriteLine("Called ConcreteStrategyA.AlgorithmInterface()");
        }
    }

    // "ConcreteStrategyB"
    class ConcreteStrategyB : Strategy
    {
        // Methods
        override public void AlgorithmInterface()
        {
            Console.WriteLine("Called ConcreteStrategyB.AlgorithmInterface()");
        }
    }

    // "Context"
    class Context
    {
        // Fields
        Strategy strategy;

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

        // Methods
        public void ContextInterface()
        {
            strategy.AlgorithmInterface();
        }
    }

    /// <summary>
    /// Client test
    /// </summary>
    public class Client
    {
        public static void Main(string[] args)
        {
            // Three contexts following different strategies
            Context c = new Context(new ConcreteStrategyA());
            c.ContextInterface();
        }
    }

using System;

namespace ConsoleApplication1
{

    #region 繼承實現

    public class Duck
    {
        public void Quack() { Console.WriteLine("Quack"); }
        public virtual void DisPlay() { Console.WriteLine("DisPlay"); }
    }

    public class MallardDuck : Duck
    {
        public override void DisPlay() { Console.WriteLine("green"); }
    }
    public class RedHeadDuck : Duck
    {
        public override void DisPlay() { Console.WriteLine("red"); }
    }
    public class RubberDuck : Duck
    {
        public override void DisPlay() { Console.WriteLine("black"); }
    }

    /* 新需求：須要加入Fly方法，但RubberDuck不該該有Fly的屬性
     * 新需求：須要加入新的Duck種類DecoyDuck，但DecoyDuck不會飛也不會叫*/

    /*問題
     * 代碼在多個子類中重複
     * 新增長的Duck很難預知其行爲
     * 運行時的行爲不容易改變 
     * 牽一髮動全身*/

    #endregion

    #region 接口實現

    public class Duck1
    {
        public void Quack() { Console.WriteLine("Quack"); }
        public virtual void DisPlay() { Console.WriteLine("DisPlay"); }
    }
    public interface IFly
    {
        void Fly();
    }
    public class MallardDuck1 : Duck1, IFly
    {
        public override void DisPlay() { Console.WriteLine("green"); }

        public void Fly()
        {
            Console.WriteLine("MallardFly");
        }
    }
    public class RedHeadDuck1 : Duck1, IFly
    {
        public override void DisPlay() { Console.WriteLine("red"); }

        public void Fly()
        {
            Console.WriteLine("RedHeadFly");
        }
    }
    public class RubberDuck1 : Duck1
    {
        public override void DisPlay() { Console.WriteLine("black"); }
    }

    /* 多種Duck實現IFly內的Fly接口都要編寫相關Fly的代碼，相同的Fly功能代碼沒法重用。 */

    #endregion

    #region 優化

    /* 方案
     * 多個Duck相同代碼的提取重複利用
     * 將變化的功能(Fly)提取成單獨的行爲實現類
     * 運行時能夠動態的賦予Duck的Fly類型 */


　　/* 這例子真是絕了。。。Duck2基類裏有IFlyBehavior接口。。。不會飛的鴨子繼承了，看起來是什麼鬼樣子。。。 */

    public class Duck2 { public void Quack() { Console.WriteLine("Quack"); } public virtual void DisPlay() { Console.WriteLine("Black"); } public IFlyBehavior m_flyBehavior; public void FlyPerform() { m_flyBehavior.Fly(); } } // 行爲類
    public interface IFlyBehavior { void Fly(); } public class FlyBehaviorA : IFlyBehavior { public void Fly() { Console.WriteLine("FlyA"); } } public class FlyBehaviorB : IFlyBehavior { public void Fly() { Console.WriteLine("FlyB"); } } public class MallardDuck2 : Duck2 { public MallardDuck2(IFlyBehavior iFly) { m_flyBehavior = iFly; } public override void DisPlay() { Console.WriteLine("green"); } } public class RedHeadDuck2 : Duck2 { public RedHeadDuck2(IFlyBehavior iFly) { m_flyBehavior = iFly; } public override void DisPlay() { Console.WriteLine("red"); } } public class RubberDuck2 : Duck2 { public override void DisPlay() { base.DisPlay(); } } #endregion

    class DuckFactory { public enum DuckType { MALLARD, REDHEAD, RUBBER } public static Duck2 CreateDuck(DuckType type) { switch (type) { case DuckType.MALLARD: return new MallardDuck2(new FlyBehaviorA()); case DuckType.REDHEAD: return new RedHeadDuck2(new FlyBehaviorB()); case DuckType.RUBBER: return new RubberDuck2(); default: Console.WriteLine("Type Error..................."); return null; } } } class Program { static void Main(string[] args) { Duck2 mallard = DuckFactory.CreateDuck(DuckFactory.DuckType.MALLARD); mallard.m_flyBehavior.Fly(); Console.ReadKey(); } } }