《大话设计模式》学习笔记22：享元模式

网站共享代码示例：

1.Flyweight：

    public abstract class WebSite
    {
        public abstract void Use();
    }

2.ConcreteeFlyweight：

    public class ConcreteWebSite:WebSite
    {
        private string webSiteCategory;
        public ConcreteWebSite(string webSiteCategory)
        {
            this.webSiteCategory = webSiteCategory;
        }
        public override void Use()
        {
            Console.WriteLine("网站分类：" + webSiteCategory);
        }
    }

3.FlyweightFactory：

    public class WebSiteFactory
    {
        private Hashtable webSites = new Hashtable();

        public WebSite GetWebSiteCategory(string key)
        {
            if(!webSites.ContainsKey(key))
            {
                webSites.Add(key, new ConcreteWebSite(key));
            }
            return (WebSite)webSites[key];
        }

        public int GetWebSiteCount()
        {
            return webSites.Count;
        }
    }

4.客户端代码：

    class Program
    {
        static void Main(string[] args)
        {
            WebSiteFactory webSiteFactory = new WebSiteFactory();

            WebSite webSiteA = webSiteFactory.GetWebSiteCategory("产品展示");
            webSiteA.Use();

            WebSite webSiteB = webSiteFactory.GetWebSiteCategory("产品展示");
            webSiteB.Use();

            WebSite webSiteC = webSiteFactory.GetWebSiteCategory("博客");
            webSiteC.Use();

            WebSite webSiteD = webSiteFactory.GetWebSiteCategory("博客");
            webSiteD.Use();

            Console.WriteLine("网站分类总数为：{0}", webSiteFactory.GetWebSiteCount());
        }
    }

内部状态与外部状态：

　　在享元对象内部并且不会随环境改变而改变的共享部分，可以称为享元对象的内部状态；而随环境改变而改变的、不可以共享的状态为外部状态。

　　享元模式可以避免大量非常相似类的开销。在程序设计中，有时需要生成大量细粒度的类实例来表示数据。如果能发现这些实例除了几个参数外基本上都是相同的，如果能把那些参数移到类实例的外面，在方法调用时将它们传递进来，就可以通过共享大幅度地减少单个实例的数目。

网站共享代码示例：

1.外部状态：

    public class User
    {
        public string Name { get; private set; }

        public User(string name)
        {
            Name = name;
        }
    }

2.Flyweight：

    public abstract class WebSite
    {
        public abstract void Use(User user);
    }

3.ConcreteeFlyweight：

    public class ConcreteWebSite : WebSite
    {
        private string webSiteCategory;

        public ConcreteWebSite(string webSiteCategory)
        {
            this.webSiteCategory = webSiteCategory;
        }
        public override void Use(User user)
        {
            Console.WriteLine("网站分类：" + webSiteCategory + "\t用户：" + user.Name);
        }
    }

4.FlyweightFactory：

    public class WebSiteFactory
    {
        private Hashtable webSites = new Hashtable();

        public WebSite GetWebSiteCategory(string key)
        {
            if(!webSites.ContainsKey(key))
            {
                webSites.Add(key, new ConcreteWebSite(key));
            }
            return (WebSite)webSites[key];
        }
        public int GetWebSiteCount()
        {
            return webSites.Count;
        }
    }

5.客户端代码：

    class Program
    {
        static void Main(string[] args)
        {
            WebSiteFactory webSiteFactory = new WebSiteFactory();

            WebSite webSiteA = webSiteFactory.GetWebSiteCategory("产品展示");
            webSiteA.Use(new User("用户A"));

            WebSite webSiteB = webSiteFactory.GetWebSiteCategory("产品展示");
            webSiteB.Use(new User("用户B"));

            WebSite webSiteC = webSiteFactory.GetWebSiteCategory("博客");
            webSiteC.Use(new User("用户C"));

            WebSite webSiteD = webSiteFactory.GetWebSiteCategory("博客");
            webSiteD.Use(new User("用户D"));

            Console.WriteLine("网站分类总数为：{0}", webSiteFactory.GetWebSiteCount());
        }
    }