策略模式定义了算法族，分别封装起来，让他们之间可以互相替换，此模式让算法的变化独立于使用算法的客户。

    abstract class Strategy{// Methodsabstract public void AlgorithmInterface();}// "ConcreteStrategyA"class ConcreteStrategyA : Strategy{// Methodsoverride public void AlgorithmInterface(){Console.WriteLine("Called ConcreteStrategyA.AlgorithmInterface()");}}// "ConcreteStrategyB"class ConcreteStrategyB : Strategy{// Methodsoverride public void AlgorithmInterface(){Console.WriteLine("Called ConcreteStrategyB.AlgorithmInterface()");}}// "Context"class Context{// Fields
        Strategy strategy;// Constructorspublic Context(Strategy strategy){this.strategy = strategy;}// Methodspublic void ContextInterface(){strategy.AlgorithmInterface();}}/// <summary>/// Client test/// </summary>public class Client{public static void Main(string[] args){// Three contexts following different strategiesContext c = new Context(new ConcreteStrategyA());c.ContextInterface();}}

using System;namespace ConsoleApplication1
{#region 继承实现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：需要加入Fly方法，但RubberDuck不应该有Fly的属性* 新需求：需要加入新的Duck种类DecoyDuck，但DecoyDuck不会飞也不会叫*//*问题* 代码在多个子类中重复* 新增加的Duck很难预知其行为* 运行时的行为不容易改变 * 牵一发动全身*/#endregion#region 接口实现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"); }}/* 多种Duck实现IFly内的Fly接口都要编写相关Fly的代码，相同的Fly功能代码无法重用。 */#endregion#region 优化/* 方案* 多个Duck相同代码的提取重复利用* 将变化的功能(Fly)提取成单独的行为实现类* 运行时可以动态的赋予Duck的Fly类型 */

　　/* 这例子真是绝了。。。Duck2基类里有IFlyBehavior接口。。。不会飞的鸭子继承了，看起来是什么鬼样子。。。 */

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();}}// 行为类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();}}#endregionclass 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();}}}