编辑说明

概述

运用共享技术有效地支持大量细粒度的对象

结构图

代码实现

享元

    /// <summary>
    /// 享元抽象
    /// </summary>
    public abstract class Flyweight
    {
        public abstract void Operation(int extrinsicstate);
    }

    /// <summary>
    /// 具体享元
    /// </summary>
    public class ConcreteFlyweight : Flyweight
    {
        public override void Operation(int extrinsicstate)
        {
            Console.WriteLine("具体Flyweight:" + extrinsicstate);
        }
    }

    /// <summary>
    /// 非享元
    /// </summary>
    public class UnsharedConcreteFlyweight : Flyweight
    {
        public override void Operation(int extrinsicstate)
        {
            Console.WriteLine("不共享的具体Flyweight:" + extrinsicstate);
        }
    }

享元工厂

    /// <summary>
    /// 享元工厂
    /// </summary>
    public class FlyweightFactory
    {
        private Hashtable flyweights = new Hashtable();
        public FlyweightFactory()
        {
            flyweights.Add("X", new ConcreteFlyweight());
            flyweights.Add("Y", new ConcreteFlyweight());
            flyweights.Add("Z", new ConcreteFlyweight());
        }
        public Flyweight GetFlyweight(string key)
        {
            return ((Flyweight)flyweights[key]);
        }
    }

客户端

    class Program
    {
        static void Main(string[] args)
        {
            int extrinsicstate = 22;

            FlyweightFactory f = new FlyweightFactory();

            Flyweight fx = f.GetFlyweight("X");
            fx.Operation(--extrinsicstate);

            Flyweight fy = f.GetFlyweight("Y");
            fy.Operation(--extrinsicstate);

            Flyweight fz = f.GetFlyweight("Z");
            fz.Operation(--extrinsicstate);

            UnsharedConcreteFlyweight uf = new UnsharedConcreteFlyweight();

            uf.Operation(--extrinsicstate);

            Console.Read();
        }
    }

运行结果

优势

相同对象只要保存一份，这降低了系统中对象的数量，从而降低了系统中细粒度对象给内存带来的压力。

使用场景

系统中有大量对象。

这些对象消耗大量内存。

这些对象的状态大部分可以外部化。

缺陷

为了使对象可以共享，需要将一些不能共享的状态外部化，这将增加程序的复杂性。

读取享元模式的外部状态会使得运行时间稍微变长。

Demo