js观察者模式

观察者模式（Publish/Subscribe），定义了一种一对多的依赖关系，让多个观察者对象同时监听某一个主题对象。这个主题对象在状态发生变化时，会通知所有观察者对象，使它们能自动更新自己。

C#观察者模式：

namespace 观察者模式
{
    class Program
    {
        static void Main(string[] args)
        {
            //老板胡汉三
            Boss huhansan = new Boss();

            //看股票的同事
            StockObserver tongshi1 = new StockObserver("魏关姹", huhansan);
            //看NBA的同事
            NBAObserver tongshi2 = new NBAObserver("易管查", huhansan);

            huhansan.Attach(tongshi1);
            huhansan.Attach(tongshi2);

            huhansan.Detach(tongshi1);

            //老板回来
            huhansan.SubjectState = "我胡汉三回来了！";
            //发出通知
            huhansan.Notify();

            Console.Read();
        }
    }

    //通知者接口
    interface Subject
    {
        void Attach(Observer observer);
        void Detach(Observer observer);
        void Notify();
        string SubjectState
        {
            get;
            set;
        }
    }

    class Secretary : Subject
    {
        //同事列表
        private IList<Observer> observers = new List<Observer>();
        private string action;

        //增加
        public void Attach(Observer observer)
        {
            observers.Add(observer);
        }

        //减少
        public void Detach(Observer observer)
        {
            observers.Remove(observer);
        }

        //通知
        public void Notify()
        {
            foreach (Observer o in observers)
                o.Update();
        }

        //前台状态
        public string SubjectState
        {
            get { return action; }
            set { action = value; }
        }
    }

    class Boss : Subject
    {
        //同事列表
        private IList<Observer> observers = new List<Observer>();
        private string action;

        //增加
        public void Attach(Observer observer)
        {
            observers.Add(observer);
        }

        //减少
        public void Detach(Observer observer)
        {
            observers.Remove(observer);
        }

        //通知
        public void Notify()
        {
            foreach (Observer o in observers)
                o.Update();
        }

        //老板状态
        public string SubjectState
        {
            get { return action; }
            set { action = value; }
        }
    }

    //抽象观察者
    abstract class Observer
    {
        protected string name;
        protected Subject sub;

        public Observer(string name, Subject sub)
        {
            this.name = name;
            this.sub = sub;
        }

        public abstract void Update();
    }

    //看股票的同事
    class StockObserver : Observer
    {
        public StockObserver(string name, Subject sub)
            : base(name, sub)
        {
        }

        public override void Update()
        {
            Console.WriteLine("{0} {1} 关闭股票行情，继续工作！", sub.SubjectState, name);
        }
    }

    //看NBA的同事
    class NBAObserver : Observer
    {
        public NBAObserver(string name, Subject sub)
            : base(name, sub)
        {
        }

        public override void Update()
        {
            Console.WriteLine("{0} {1} 关闭NBA直播，继续工作！", sub.SubjectState, name);
        }
    }
}

在.NET中，我们可以使用委托与事件来简化观察者模式的实现，上面的例子用事件和委托的实现如下代码所示：

namespace 观察者模式_委托
{
    class Program
    {
        static void Main(string[] args)
        {
            //老板胡汉三
            Boss huhansan = new Boss();

            //看股票的同事
            StockObserver tongshi1 = new StockObserver("魏关姹", huhansan);
            //看NBA的同事
            NBAObserver tongshi2 = new NBAObserver("易管查", huhansan);

            huhansan.Update += new EventHandler(tongshi1.CloseStockMarket);
            huhansan.Update += new EventHandler(tongshi2.CloseNBADirectSeeding);

            //老板回来
            huhansan.SubjectState = "我胡汉三回来了！";
            //发出通知
            huhansan.Notify();

            Console.Read();


        }
    }

    //通知者接口
    interface Subject
    {
        void Notify();
        string SubjectState
        {
            get;
            set;
        }
    }

    //事件处理程序的委托
    delegate void EventHandler();

    class Secretary : Subject
    {
        //声明一事件Update，类型为委托EventHandler
        public event EventHandler Update;

        private string action;

        public void Notify()
        {
            Update();
        }
        public string SubjectState
        {
            get { return action; }
            set { action = value; }
        }
    }

    class Boss : Subject
    {
        //声明一事件Update，类型为委托EventHandler
        public event EventHandler Update;

        private string action;

        public void Notify()
        {
            Update();
        }
        public string SubjectState
        {
            get { return action; }
            set { action = value; }
        }
    }

    //看股票的同事
    class StockObserver
    {
        private string name;
        private Subject sub;
        public StockObserver(string name, Subject sub)
        {
            this.name = name;
            this.sub = sub;
        }

        //关闭股票行情
        public void CloseStockMarket()
        {
            Console.WriteLine("{0} {1} 关闭股票行情，继续工作！", sub.SubjectState, name);
        }
    }

    //看NBA的同事
    class NBAObserver
    {
        private string name;
        private Subject sub;
        public NBAObserver(string name, Subject sub)
        {
            this.name = name;
            this.sub = sub;
        }

        //关闭NBA直播
        public void CloseNBADirectSeeding()
        {
            Console.WriteLine("{0} {1} 关闭NBA直播，继续工作！", sub.SubjectState, name);
        }
    }
}

js观察者模式：

var event = {
            clientList:[],
            listen:function(key,fn){
                if(!this.clientList[key]){
                    this.clientList[key] = [];
                }
                this.clientList[key].push(fn); //订阅的消息加进缓存列表
            },
            trigger:function(){
                var key = Array.prototype.shift.call(arguments),
                    fns = this.clientList[key];
                   
                if(!fns || fns.length === 0){  //如果没有绑定对应的消息
                    return false;
                }
               
                for(var i =0, fn; fn=fns[i++];){
                    fn.apply(this,arguments);
                }
            },
            remove:function(key,fn){
                var fns = this.clientList[key];
               
                if(!fns){   //如果key对应的消息没有被人订阅，则直接返回
                    return false;
                }
                if(!fn){    //如果没有传入具体的回调函数，表示需要取消key对应的所有订阅
                    fns && (fns.length = 0);
                }else{
                    for(var i=fns.length - 1; i>=0;i--){
                        var _fn = fns[i];
                        if(_fn === fn){
                            fns.splice(i,1);  //删除订阅者的回调函数
                        }
                    }
                }
            }
        };


//调用：
var salesOffices = {};
$.extend(salesOffices,event);

salesOffices.listen('squareMeter',function(price){
    alert('价格=' + price);
});
salesOffices.trigger('squareMeter',20000);

//全局调用：
event.listen('squareMeter',function(price){
    alert('价格=' + price);
});
event.trigger('squareMeter',20000);