設(shè)計模式-觀察者模式

//主題
interface Subject
    {
        void Notify();
        string msg { get; set; }
        UpdateHandler Update { get; set; }
    }
    delegate void UpdateHandler();
    class ChildSubject : Subject
    {
        public UpdateHandler Update { get; set; }
        public string msg { get; set; }        

        public void Notify()
        {
            Update();
        }
    }
//觀察者       
abstract class Observer
    {
        public string name;
        public Subject subject;
        public Observer(string _name, Subject _subject)
        {
            name = _name;
            subject = _subject;
        }
    }
    class Site: Observer
    {
        public Site(string _name, Subject _subject) : base(_name, _subject)
        {
        }

        public void RefreshSite()
        {
            Console.WriteLine("{0},{1}需要同步更新", subject.msg,name);
        }
    }
    class App: Observer
    {
        public App(string _name, Subject _subject) : base(_name, _subject)
        {
        }
        //方法名稱不一樣，所以抽象沒意義
        public void RefreshApp()
        {
            Console.WriteLine("{0},{1}需要同步更新", subject.msg, name);
        }
    }
        //前端
        static void Main(string[] args)
        {
            Subject subject = new ChildSubject();
            Site site = new Site("電腦網(wǎng)站", subject);
            App app = new App("手機APP", subject);
            subject.msg = "數(shù)據(jù)庫被更新了";
            subject.Update += site.RefreshSite;
            subject.Update += app.RefreshApp;
            subject.Notify();
            Console.ReadLine();
        } 

總結(jié)：觀察者模式適用于某個對象發(fā)生變化后會引起其他對象發(fā)生連鎖反應(yīng)的情況下，（兩個類有依賴關(guān)系的情況下）。