观察者模式 The Observer Pattern

        <FONT size=+0><FONT size=+0>
        /// <summary>
        /// 主题对象
        /// </summary>
            public interface ISubject
            {
                List<IObserver> Observers
                {
                    get;
                    set;
                }
                void RegisterObserver(IObserver observer);
                void RemoveObserver(IObserver observer);
                void NotifyObservers(string command);
            }
        /// <summary>
        /// 观察者
        /// </summary>
            public interface IObserver
            {
                void Update(string command);
            }
        </FONT></FONT>

        <FONT size=3>
        /// <summary>
        /// 司令官
        /// </summary>
            public class Commander : ISubject
            {
                #region ISubject 成员
                private List<IObserver> _observers;
                public List<IObserver> Observers
                {
                    get
                    {
                        return _observers;
                    }
                    set
                    {
                        _observers = value;
                    }
                }

                public Commander()
                {
                    _observers = new List<IObserver>();
                }

                public void RegisterObserver(IObserver observer)
                {
                    this.Observers.Add(observer);
                }

                public void RemoveObserver(IObserver observer)
                {
                    this.Observers.Remove(observer);
                }

                public void NotifyObservers(string command)
                {
                    foreach (IObserver observer in this.Observers)
                    {
                        observer.Update(command);
                    }
                }

                #endregion

                public void SetCommand(string command)
                {
                    Console.WriteLine(string.Format("司令官下命令：{0}", command));
                    NotifyObservers(command);
                }
            }
        </FONT>

        <FONT size=3>
        /// <summary>
        /// 斧头小队
        /// </summary>
            public class AxeTeam : IObserver
            {
                #region IObserver 成员

                public void Update(string command)
                {
                    switch (command)
                    {
                        case "攻击":
                            Console.WriteLine("斧头小队：用斧头攻击，势死如归！");
                            break;
                        case "撤退":
                            Console.WriteLine("斧头小队：坚守阵地，死也不放弃！");
                            break;
                    }
                }

                #endregion
            }

        /// <summary>
        /// 弓箭手小队
        /// </summary>
            public class BowAndArrowTeam : IObserver
            {
                #region IObserver 成员

                public void Update(string command)
                {
                    switch (command)
                    {
                        case "攻击":
                            Console.WriteLine("弓箭手小队：弓箭手掩护，退后十步，射箭！");
                            break;
                        case "撤退":
                            Console.WriteLine("弓箭手小队：边撤退，边掩护斧头小队！");
                            break;
                    }
                }

                #endregion
            }

        /// <summary>
        /// 匕首小队
        /// </summary>
            public class KnifeTeam : IObserver
            {
                #region IObserver 成员

                public void Update(string command)
                {
                    switch (command)
                    {
                        case "攻击":
                            Console.WriteLine("匕首小队：匕首攻击，打不过就跑！");
                            break;
                        case "撤退":
                            Console.WriteLine("匕首小队：快撤啊，我军大势已去！");
                            break;
                    }
                }

                #endregion
            }
        </FONT>

        <FONT size=+0>

        //实例化司令官和三个小队

        Commander commander = new Commander();

        AxeTeam axe = new AxeTeam();

        BowAndArrowTeam baa = new BowAndArrowTeam();

        KnifeTeam knife = new KnifeTeam();

        //注册观察者

        commander.RegisterObserver(axe);

        commander.RegisterObserver(baa);

        commander.RegisterObserver(knife);

        //司令官下命令

        commander.SetCommand("攻击");

        commander.SetCommand("撤退");

        //匕首小队怕死，从军队中删除

        commander.RemoveObserver(knife);

        //司令官再次下命令

        commander.SetCommand("攻击");

        commander.SetCommand("撤退");</FONT>