观察者模式

namespace ConsoleApplication1
{
    /// <summary>
    /// 发布信息者
    /// </summary>
    public interface ISubject
    {
        /// <summary>
        /// 用于登记需要推送的用户
        /// </summary>
        /// <param name="observer"></param>
        void RegisterObserver(IObServer observer);
        /// <summary>
        /// 将用户剔除出推送列表
        /// </summary>
        /// <param name="observer"></param>
        void RemoveObserver(IObServer observer);
        /// <summary>
        /// 推送服务
        /// </summary>
        void NotifyObserver();
    }

    /// <summary>
    /// 信息接受者
    /// </summary>
    public interface IObServer
    {
        /// <summary>
        /// 当Subject信息发送时，用于更新
        /// </summary>
        /// <param name="msg"></param>
        void Update(string msg);
    }

    /// <summary>
    /// 新闻集团
    /// </summary>
    public class NewsGrop : ISubject
    {
        private string _NewsId;

        IList<IObServer> services;
        public NewsGrop()
        {
            services = new List<IObServer>();
        }

        /// <summary>
        /// 订阅报刊
        /// </summary>
        /// <param name="customer"></param>
        public void RegisterObserver(IObServer customer)
        {
            services.Add(customer);
        }

        /// <summary>
        /// 发行报刊
        /// </summary>
        /// <param name="newId"></param>
        public void NotifyObserver()
        {
            Console.WriteLine(string.Format("{0}发行！", _NewsId));
            foreach (var item in services)
            {
                item.Update(_NewsId);
            }
        }


        public void RemoveObserver(IObServer customer)
        {
            if (services.IndexOf(customer) != 0)
            {
                services.Remove(customer);
            }
        }

        public void SetNewsId(string newsId)
        {
            this._NewsId = newsId;
        }
    }

    /// <summary>
    /// 收藏爱好者
    /// </summary>
    public class Collector : IObServer
    {

        public Collector()
        {
        }

        public void Update(string msg)
        {
            Console.WriteLine(string.Format("收藏{0}...", msg));
        }
    }

    /// <summary>
    /// 一般用户
    /// </summary>
    public class GeneralUser : IObServer
    {

        public GeneralUser()
        {
        }
        public void Update(string msg)
        {
            Console.WriteLine(string.Format("慢慢阅读{0}...", msg));
        }
    }

    /// <summary>
    /// 主程序
    /// </summary>
    class Program
    {
        static void Main(string[] args)
        {
            NewsGrop news = new NewsGrop();
            Collector c1 = new Collector();

            GeneralUser g1 = new GeneralUser();
            GeneralUser g2 = new GeneralUser();
            news.RegisterObserver(c1);
            news.RegisterObserver(g1);
            news.RegisterObserver(g2);

            news.SetNewsId(string.Format("第{0}期", 1));
            news.NotifyObserver();
            Console.WriteLine();

            news.RemoveObserver(g2);
            news.SetNewsId(string.Format("第{0}期", 2));
            news.NotifyObserver();
            Console.WriteLine();

            Console.ReadLine();
        }
    }
}