行为型模式-观察者模式

男娘i 2022-05-23 13:40 164阅读 0赞

对象间的一种一对多的依赖关系，当一个对象的状态发生改变时，所有依赖于它的对象都得到通知并被自动更新。

Subject 抽象的主题，被观察的对象，提供Attach和Detach Observer对象的接口。

ConcreteSubject具体的被观察对象，维持ConcreteSubject状态。当状态发生变化时，发送消息通知它的观察者。

Observer：抽象的观察者，定义一个发送变化通知更新的接口。

ConcreteObserver：具体观察者，实现抽象观察者定义的更新接口，以便在得到主题更改通知时更新自身的状态。

观察者模式特点：降低业务逻辑耦合，将主逻辑和非主逻辑分开。但如果观察者比较多，可能会对系统的运行效率有影响，建议使用异步方式操作。在观察者模式中，观察者一般不返回结果。

结构图：

![20180610103512139][]

![20180610103522179][]

namespace Libraries.Test.DesignPattern.Observer
    {
        public interface Subject
        {
            /// <summary>
            /// 添加订阅者
            /// </summary>
            /// <param name="observer"></param>
            void Attach(MsgObserver observer);
    
            /// <summary>
            /// 删除订阅者
            /// </summary>
            /// <param name="observer"></param>
            void Detach(MsgObserver observer);
    
            /// <summary>
            /// 通知订阅者
            /// </summary>
            /// <param name="message"></param>
            void Notify(String message);
        }
    }

namespace Libraries.Test.DesignPattern.Observer
    {
        /// <summary>
        /// 被观察者
        /// </summary>
        public class MsgSubject : Subject
        {
            private List<MsgObserver> observers = new List<MsgObserver>();
    
            /// <summary>
            /// 添加观察者对象
            /// </summary>
            /// <param name="observer"></param>
            public void Attach(MsgObserver observer)
            {
                observers.Add(observer);
            }
    
            /// <summary>
            /// 移除观察者对象
            /// </summary>
            /// <param name="observer"></param>
            public void Detach(MsgObserver observer)
            {
                observers.Remove(observer);
            }
    
            /// <summary>
            /// 通知观察者对象
            /// </summary>
            public void Notify(string message)
            {
                foreach (MsgObserver o in observers)
                {
                    o.Update(message);
                }
            }
        }
    }

namespace Libraries.Test.DesignPattern.Observer
    {
        /// <summary>
        /// 观察者
        /// </summary>
        public interface MsgObserver
        {
             void Update(string contact);
        }
    }

namespace Libraries.Test.DesignPattern.Observer
    {
        public class AddFileLog : MsgObserver
        {
            private string subject;
            public AddFileLog(string subject)
            {
                this.subject = subject;
            }
    
            /// <summary>
            /// 执行写文件日志操作
            /// </summary>
            /// <param name="contact"></param>
            public void Update(string contact)
            {
                string str = subject + "," + contact;
                return;
            }
        }
    }

namespace Libraries.Test.DesignPattern.Observer
    {
        public class SendEmail : MsgObserver
        {
            private string subject;
            public SendEmail(string subject)
            {
                this.subject = subject;
            }
    
            /// <summary>
            /// 执行发邮件操作
            /// </summary>
            /// <param name="contact"></param>
            public void Update(string contact)
            {
                string str = subject + "," + contact;
                return;
            }
        }
    }

namespace Libraries.Test.DesignPattern.Observer
    {
        public class SendSms : MsgObserver
        {
            private string subject;
            public SendSms(string subject)
            {
                this.subject = subject;
            }
    
            /// <summary>
            /// 执行发送短信操作
            /// </summary>
            /// <param name="contact"></param>
            public void Update(string contact)
            {
                string str = subject + "," + contact;
                return;
            }
        }
    }

namespace Libraries.Test.DesignPattern.Observer
    {
        public class SendMessage : MsgObserver
        {
            private string subject;
            public SendMessage(string subject)
            {
                this.subject = subject;
            }
    
            /// <summary>
            /// 执行发送站内信操作
            /// </summary>
            /// <param name="contact"></param>
            public void Update(string contact)
            {
                string str = subject + "," + contact;
                return;
            }
        }
    }

namespace Libraries.Test.DesignPattern.Observer
    {
        public class Client
        {
            public void Excute()
            {
                MsgSubject subject = new MsgSubject();
                subject.Attach(new SendSms("发送短信"));
                subject.Attach(new SendEmail("发送邮件"));
                subject.Attach(new SendMessage("发送站内信"));
                subject.Attach(new AddFileLog("添加日志"));
                subject.Notify("内容");
            }
        }
    }

[20180610103512139]: /images/20220523/530f02e4ae844c2da660a74928b443c5.png
[20180610103522179]: /images/20220523/33b473fa71e34259ad569d78edf9d2db.png