观察者模式(二)

 

//实现的是在手机、电脑、平板上都能够更新显示天气

abstract class Subject
    {
        private IList<Observer> observers = new List<Observer>();

        //增加观察者
        public void Attach(Observer observer)
        {
            observers.Add(observer);
        }
        //移除观察者
        public void Detach(Observer observer)
        {
            observers.Remove(observer);
        }
        //通知
        public void Notify()
        {
            foreach (Observer o in observers)
            {
                o.Update();
            }
        }
    }

    //具体通知者
    class ConcreteSubject : Subject
    {
        private string subjectState;

        //具体通知者状态
        public string SubjectState
        {
            get { return subjectState; }
            set { subjectState = value; }
        }
    }

    abstract class Observer
    {
        public abstract void Update();
    }

    class ConcreteObserver : Observer
    {
        private string name;  //观察者名称
        private string observerState; //通知内容
        private ConcreteSubject subject; //通知者

        public ConcreteObserver(
          ConcreteSubject subject, string name)
        {
            this.subject = subject;
            this.name = name;
        }
        //更新
        public override void Update()
        {
            observerState = subject.SubjectState;
            Console.WriteLine("{0}的新天气状态是{1}",
              name, observerState);
        }
    }

private void button4_Click(object sender, EventArgs e)
        {
            ConcreteSubject s = new ConcreteSubject();

            s.Attach(new ConcreteObserver(s, "手机"));
            s.Attach(new ConcreteObserver(s, "电脑"));
            s.Attach(new ConcreteObserver(s, "平板"));

            s.SubjectState = "晴";
            s.Notify();
        }