设计模式》观察者模式

例子

教会（Subject）
教会成员（Observer）

public class GuildSubject
    {
        private List<AbsSubscriber<GuildSubject>> _subscribers;

        public GuildSubject(string guildName)
        {
            GuildName = guildName;
            _subscribers = new List<AbsSubscriber<GuildSubject>>();
        }

        public void AddObserver(AbsSubscriber<GuildSubject> obj)
        {
            _subscribers.Add(obj);
        }

        public void RemoveObserver(AbsSubscriber<GuildSubject> obj)
        {
            _subscribers.Remove(obj);
        }

        public void SendData(string data)
        {
            foreach (var subscriber in _subscribers)
            {
                subscriber.ReceiveData(this, data);
            }
        }


        public string GuildName { get; }
    }

    public interface IObserver<Subject>
    {
        void ReceiveData(Subject subject, string data);
    }

    public abstract class AbsSubscriber<Subject> : IObserver<Subject>
    {
        public AbsSubscriber(string name)
        {
            Name = name;
        }

        public string Name { get; }

        public abstract void ReceiveData(Subject subject, string data);
    }

    public class GuildSubscriber : AbsSubscriber<GuildSubject>
    {
        public GuildSubscriber(string name) : base(name)
        {
        }

        public override void ReceiveData(GuildSubject subject, string data)
        {
            Console.WriteLine($"{this.Name}收到{subject.GuildName}教会的消息：{data}");
        }
    }

        private static void SubjectTest()
        {
            var guildSubject = new GuildSubject("牛逼教会");

            guildSubject.AddObserver(new GuildSubscriber("信徒1"));
            guildSubject.AddObserver(new GuildSubscriber("信徒2"));
            guildSubject.AddObserver(new GuildSubscriber("信徒3"));

            guildSubject.SendData("牛逼起来啦");
        }