23种设计模式：观察者模式，第一次对观察者模式理解的这么通透。

class Program
    {
        static void Main(string[] args)
        {
            Subject sub1 = new Subject();
            Observer_1 ob1 = new Observer_1("NO.1");
            Observer_1 ob2 = new Observer_1("NO.2");
            sub1.AddObserver(ob1);
            sub1.AddObserver(ob2);
            sub1.Notify();
            Console.Read();
        }
    }

    class Subject
    {
        private List<IObserverable> observerContainer = new List<IObserverable>();

        public void AddObserver(IObserverable observer)
        {
            this.observerContainer.Add(observer);
        }

        public void RemoveObserver(IObserverable observer)
        {
            this.observerContainer.Remove(observer);
        }

        public void Notify()
        {
            foreach (IObserverable o in this.observerContainer)
            {
                Console.WriteLine(o.ObserverName);
                o.Update();
            }
        }

    }

    interface IObserverable
    {
        string ObserverName { get; }
        void Update();
    }

    class Observer_1 : IObserverable
    {
        private string _ObserverName;

        public Observer_1(string observerName)
        {
            this._ObserverName = observerName;
        }

        public string ObserverName
        {
            get { return _ObserverName; }
        }

        public void Update()
        {
            Console.WriteLine(this.ObserverName + ": Is updated.");
        }
    }

    class Observer_2 : IObserverable
    {
        private string _ObserverName;

        public Observer_2(string observerName)
        {
            this._ObserverName = observerName;
        }

        public string ObserverName
        {
            get { return _ObserverName; }
        }

        public void Update()
        {
            Console.WriteLine(this.ObserverName + ": Is updated.");
        }
    }