Flyweight Design

用来支持大量重复的数据的存储，比如很多相同的图元要存储在不同的图片/文档。

1）Flyweight:能对extrinsic state（外在状态）接收 和相应的接口。

 

public abstract class Flyweight

    {

        public abstract void Operation(int extrinsicState);

    }

2) ConcereteFlyweight:实现Flyweight接口的类

 

public class ConcreteFlyweight : Flyweight

    {

        public override void Operation(int extrinsicState)

        {

            Console.WriteLine("Concrete Flyweight "+extrinsicState);

        }

    }

3)FlyweightFacotory:（Hashtable/Dictionary）

 1.负责创建和管理Flyweight objects

 2.确保flyweight能够被正确的共享。如果客户请求一个Flyweight,首先检查存在，如果存在，则返回；否则新创建一个对象。

 

public class FlyweightFactory

    {

        private static readonly Hashtable flyweights = new Hashtable();

        public static Flyweight GetFlyweight(int key)

        {

            if (flyweights.Contains(key))

                return flyweights[key] as Flyweight;

 

            flyweights.Add(key, new ConcreteFlyweight());

            return flyweights[flyweights.Count] as Flyweight; 

        }

    }

 

 

4).客户端：只有Flyweight的引用，并且负责保持/存储extrinsicSate（外在的状态信息）。

 

 

public class Client1

    {

        void Call()

        {

            // Arbitrary extrinsic state

            int extrinsicstate = 1;

            Flyweight flyweight1 = FlyweightFactory1.GetFlyweight(extrinsicstate);

            flyweight1.Operation(extrinsicstate);

            extrinsicstate--;

 

            Flyweight flyweight2 = FlyweightFactory1.GetFlyweight(extrinsicstate);

            flyweight2.Operation(extrinsicstate);

            extrinsicstate += 1;

        }

    }