Observer模式（观察者模式）

客官°小女子只卖身不卖艺 2024-03-31 14:30 67阅读 0赞

#### 模式简介 ####

当一个对象触发某个事件时，其它对象会根据该对象和该事件作出不同响应，这个时候就可以采用观察者模式。

#### 模式UML图 ####

![1c2a0389c1534d2a8e29f8401553f80f.jpeg][]

#### 代码示例（C\#） ####

**提示：**可在本栏目的资源篇“[设计模式代码示例合集][Link 1]”下载所有完整代码资源。

//被观察者：邮件发送者
        class EmailSender : ObservedOject
        {
            public EmailSender()
            {
                observedEvent = new EmailEvent(this);
            }
            public override void Add(Monitor p_monitor)
            {
                monitors.Add(p_monitor);
            }
    
            public override void DoActions()
            {
                foreach (Monitor m in monitors)
                {
                    m.DoAction(observedEvent);
                }
            }
    
            public override void DoEvent()
            {
                observedEvent.CustomEvent();
            }
    
            public override void Remove(Monitor p_monitor)
            {
                monitors.Remove(p_monitor);
            }
        }
    
        //邮件发送者所触发的事件
        class EmailEvent : ObservedEvent
        {
            public EmailEvent(ObservedOject p_source)
            {
                source = p_source;
            }
            public override void CustomEvent()
            {
                Console.WriteLine("EmailEvent is started.");
            }
    
            public override ObservedOject GetSource()
            {
                return source;
            }
        }
    
        //观察者：游戏玩家
        class GamePlayer : Monitor
        {
            private string name;
            public GamePlayer(string p_name)
            {
                name = p_name;
            }
            public override void DoAction(ObservedEvent p_event)
            {
                Console.WriteLine(name + " recieve one email.");
            }
        }
    
        //作为观察者的基类
        public abstract class Monitor
        {
            public abstract void DoAction(ObservedEvent p_event);
        }
    
        //作为被观察者的基类
        public abstract class ObservedOject
        {
            protected List<Monitor> monitors = new List<Monitor>();
            protected ObservedEvent observedEvent;
    
            public abstract void Add(Monitor p_monitor);
            public abstract void Remove(Monitor p_monitor);
            public abstract void DoEvent();
            public abstract void DoActions();
        }
    
        //被观察者所触发事件的基类
        public abstract class ObservedEvent
        {
            protected ObservedOject source;
            public abstract void CustomEvent();
            public abstract ObservedOject GetSource();
        }
    
        //测试代码
        public void Test()
        {
            GamePlayer player1 = new GamePlayer("KaKa");
            GamePlayer player2 = new GamePlayer("JoJo");
            EmailSender emailSender = new EmailSender();
            emailSender.Add(player1);
            emailSender.Add(player2);
            emailSender.DoEvent();
            emailSender.DoActions();
        }

#### 代码解说 ####

我们这里是EmailSender作为事件触发对象，触发的事件是发送邮件，当发送邮件后，两个游戏玩家作为观察者会显示接收到邮件的提示信息，那么玩家可能会立即阅读邮件，也可能暂不阅读邮件，所以对于玩家来说可以作出不同的反应，DoEvent()是触发发送邮件的事件，DoActions()是调用观察者的行为方法。

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[1c2a0389c1534d2a8e29f8401553f80f.jpeg]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/31/3567957211ed4c6ab7c2de4dbdca7b94.jpeg
[Link 1]: https://blog.csdn.net/hgf1037882434/article/details/128394782