设计模式：
观察者模式（Observer Pattern）
简单介绍：
观察者模式(Observer Pattern)是设计模式中行为模式的一种，它解决了上述具有一对多依赖关系的对象的重用问题。此模式的参与者分为两大类，一类是被观察的目标，另一类是观察该目标的观察者们。正因为该模式是基于“一对多”的关系，所以该模式一般是应用于由一个目标对象和N个观察者对象组成（当然也可以扩展为有多个目标对象，但我们现在只讨论前者）的场合。当目标对象的状态发生改变或做出某种行为时，正在观察该目标对象的观察者们将自动地、连锁地作出相应的响应行为。
模式中具有的角色
- 抽象主题（Subject）：它把所有观察者对象的引用保存到一个聚集里，每个主题都可以有任何数量的观察者。抽象主题提供一个接口，可以增加和删除观察者对象。
- 具体主题（ConcreteSubject）：将有关状态存入具体观察者对象；在具体主题内部状态改变时，给所有登记过的观察者发出通知。
- 抽象观察者（Observer）：为所有的具体观察者定义一个接口，在得到主题通知时更新自己。
- 具体观察者（ConcreteObserver）：实现抽象观察者角色所要求的更新接口，以便使本身的状态与主题状态协调。
举例子：博客的例子就是一个观察者模式，比如你关注一些作者的博客，当作者有博客发布时候，你就会收到一条该作者发布的博客的消息。
抽象主题：Blog 博客
具体主题：MyBlog 的博客
抽象观察者：IObserver
具体的观察者：Observer
观察者模式类图：
观察者模式C#代码举例
订阅博客抽象类
1 /***************************************************** 2 * ProjectName: _11DesignPattern_Observer 3 * Description: 4 * ClassName: Blog 5 * CLRVersion: 4.0.30319.18408 6 * Author: JiYF 7 * NameSpace: _11DesignPattern_Observer 8 * MachineName: JIYONGFEI 9 * CreateTime: 2017/5/23 17:08:10 10 * UpdatedTime: 2017/5/23 17:08:10 11 *****************************************************/ 12 using System; 13 using System.Collections.Generic; 14 using System.Linq; 15 using System.Text; 16 17 namespace _11DesignPattern_Observer 18 { 19 /// <summary> 20 /// 订阅博客抽象类 21 /// </summary> 22 public abstract class Blog 23 { 24 /// <summary> 25 /// 保存订阅者列表 26 /// </summary> 27 private List<IObserver> observers = new List<IObserver>(); 28 29 /// <summary> 30 /// 博主名 31 /// </summary> 32 public string BlogName { get; set; } 33 34 /// <summary> 35 /// 博客标题 36 /// </summary> 37 public string BlogTitle { get; set; } 38 39 /// <summary> 40 /// 博客信息 41 /// </summary> 42 public string BlogInfo { get; set; } 43 44 /// <summary> 45 /// 博客构造函数 46 /// </summary> 47 /// <param name="blogTitle">博客标题</param> 48 /// <param name="blogInfo">博客信息</param> 49 public Blog(string name,string blogTitle,string blogInfo) 50 { 51 this.BlogName = name; 52 this.BlogTitle = blogTitle; 53 this.BlogInfo = blogInfo; 54 } 55 56 /// <summary> 57 /// 添加一个订阅者 58 /// </summary> 59 /// <param name="observer">具体的订阅者对象</param> 60 public void AddObserver(IObserver observer) 61 { 62 if (observers.Contains(observer)) 63 { 64 return; 65 } 66 observers.Add(observer); 67 } 68 69 /// <summary> 70 /// 删除一个订阅者 71 /// </summary> 72 /// <param name="observer">具体的订阅者对象</param> 73 public void RemoveObserver(IObserver observer) 74 { 75 if (observers.Contains(observer)) 76 { 77 observers.Remove(observer); 78 } 79 } 80 81 /// <summary> 82 /// 发布博客通知 83 /// </summary> 84 public void PublishBlog() 85 { 86 //遍历通知每一个订阅者 87 foreach (IObserver ob in observers) 88 { 89 if (ob != null) 90 { 91 ob.Receive(this); 92 } 93 } 94 } 95 96 } 97 }
具体的博客类
1 /***************************************************** 2 * ProjectName: _11DesignPattern_Observer 3 * Description: 4 * ClassName: JiYFBlog 5 * CLRVersion: 4.0.30319.18408 6 * Author: JiYF 7 * NameSpace: _11DesignPattern_Observer 8 * MachineName: JIYONGFEI 9 * CreateTime: 2017/5/23 17:21:23 10 * UpdatedTime: 2017/5/23 17:21:23 11 *****************************************************/ 12 using System; 13 using System.Collections.Generic; 14 using System.Linq; 15 using System.Text; 16 17 namespace _11DesignPattern_Observer 18 { 19 20 /// <summary> 21 /// 具体的订阅博客类 22 /// </summary> 23 public class JiYFBlog :Blog 24 { 25 public JiYFBlog(string name,string blogTitile, string blogInfo) 26 : base(name,blogTitile,blogInfo) 27 { 28 29 } 30 } 31 }
订阅者接口类
1 /***************************************************** 2 * ProjectName: _11DesignPattern_Observer 3 * Description: 4 * ClassName: IObserver 5 * CLRVersion: 4.0.30319.18408 6 * Author: JiYF 7 * NameSpace: _11DesignPattern_Observer 8 * MachineName: JIYONGFEI 9 * CreateTime: 2017/5/23 17:09:28 10 * UpdatedTime: 2017/5/23 17:09:28 11 *****************************************************/ 12 using System; 13 using System.Collections.Generic; 14 using System.Linq; 15 using System.Text; 16 17 namespace _11DesignPattern_Observer 18 { 19 /// <summary> 20 /// 订阅者接口 21 /// </summary> 22 public interface IObserver 23 { 24 25 void Receive(Blog blog); 26 } 27 }
具体的订阅者类：
1 /***************************************************** 2 * ProjectName: _11DesignPattern_Observer 3 * Description: 4 * ClassName: Observer 5 * CLRVersion: 4.0.30319.18408 6 * Author: JiYF 7 * NameSpace: _11DesignPattern_Observer 8 * MachineName: JIYONGFEI 9 * CreateTime: 2017/5/23 17:23:36 10 * UpdatedTime: 2017/5/23 17:23:36 11 *****************************************************/ 12 using System; 13 using System.Collections.Generic; 14 using System.Linq; 15 using System.Text; 16 17 namespace _11DesignPattern_Observer 18 { 19 /// <summary> 20 /// 具体的订阅者类 21 /// </summary> 22 public class Observer :IObserver 23 { 24 /// <summary> 25 /// 订阅者名字 26 /// </summary> 27 private string m_Name; 28 public string Name 29 { 30 get { return m_Name; } 31 set { m_Name = value; } 32 } 33 34 /// <summary> 35 /// 订阅者构造函数 36 /// </summary> 37 /// <param name="name">订阅者名字</param> 38 public Observer(string name) 39 { 40 this.m_Name = name; 41 } 42 43 /// <summary> 44 /// 订阅者接受函数 45 /// </summary> 46 /// <param name="blog"></param> 47 public void Receive(Blog blog) 48 { 49 Console.WriteLine("订阅者:\"{0}\"观察到了:{1}发布的一篇博客,标题为:{2},内容为:{3}",Name,blog.BlogName,blog.BlogTitle,blog.BlogInfo); 50 } 51 } 52 }
测试代码：
1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5 6 namespace _11DesignPattern_Observer 7 { 8 class Client 9 { 10 static void Main(string[] args) 11 { 12 Console.WriteLine("--全部订阅者--"); 13 //创建一个JiYF的博客 14 Blog jiyfBlog = new JiYFBlog("JiYF笨小孩","丑小鸭","丑小鸭的故事"); 15 16 //创建订阅者 17 Observer obsZhangsan = new Observer("张三"); 18 Observer obsLiSi = new Observer("李四"); 19 Observer obsWangwu = new Observer("王五"); 20 21 //添加对JiYF博客的订阅者 22 jiyfBlog.AddObserver(obsZhangsan); 23 jiyfBlog.AddObserver(obsLiSi); 24 jiyfBlog.AddObserver(obsWangwu); 25 26 //通知订阅者 27 jiyfBlog.PublishBlog(); 28 29 Console.WriteLine("--移除订阅者张三--"); 30 jiyfBlog.RemoveObserver(obsZhangsan); 31 jiyfBlog.PublishBlog(); 32 Console.ReadLine(); 33 } 34 } 35 }
运行结果：
通常在C#代码中，观察者模式一般采用委托来实现如下所示
委托实现观察者模式
抽象博客类：
1 /***************************************************** 2 * ProjectName: _11DesignPattern_ObserverDelegateTest 3 * Description: 4 * ClassName: Blog 5 * CLRVersion: 4.0.30319.42000 6 * Author: JiYF 7 * NameSpace: _11DesignPattern_ObserverDelegateTest 8 * MachineName: JIYF_PC 9 * CreateTime: 2017/5/23 20:48:00 10 * UpdatedTime: 2017/5/23 20:48:00 11 *****************************************************/ 12 using System; 13 using System.Collections.Generic; 14 using System.Linq; 15 using System.Text; 16 17 namespace _11DesignPattern_ObserverDelegateTest 18 { 19 /// <summary> 20 /// 委托充当订阅者接口类 21 /// </summary> 22 /// <param name="sender"></param> 23 public delegate void NotifyEventHandler(object sender); 24 25 /// <summary> 26 /// 订阅博客基类 27 /// </summary> 28 public class Blog 29 { 30 public NotifyEventHandler NotifyEvent; 31 /// <summary> 32 /// 博主名 33 /// </summary> 34 public string BlogName { get; set; } 35 36 /// <summary> 37 /// 博客标题 38 /// </summary> 39 public string BlogTitle { get; set; } 40 41 /// <summary> 42 /// 博客信息 43 /// </summary> 44 public string BlogInfo { get; set; } 45 46 /// <summary> 47 /// 博客构造函数 48 /// </summary> 49 /// <param name="blogTitle">博客标题</param> 50 /// <param name="blogInfo">博客信息</param> 51 public Blog(string name, string blogTitle, string blogInfo) 52 { 53 this.BlogName = name; 54 this.BlogTitle = blogTitle; 55 this.BlogInfo = blogInfo; 56 } 57 58 /// <summary> 59 /// 绑定订阅事件 60 /// </summary> 61 /// <param name="ob">订阅者</param> 62 public void AddObserver(NotifyEventHandler observer) 63 { 64 NotifyEvent += observer; 65 } 66 67 /// <summary> 68 /// 取消绑定订阅 69 /// </summary> 70 /// <param name="observer"></param> 71 public void RemoteObserver(NotifyEventHandler observer) 72 { 73 NotifyEvent -= observer; 74 } 75 76 /// <summary> 77 /// 发布博客通知 78 /// </summary> 79 public void PublishBlog() 80 { 81 if(NotifyEvent != null) 82 { 83 NotifyEvent(this); 84 } 85 } 86 } 87 }
具体的博客类
1 /***************************************************** 2 * ProjectName: _11DesignPattern_ObserverDelegateTest 3 * Description: 4 * ClassName: JiYFBlog 5 * CLRVersion: 4.0.30319.42000 6 * Author: JiYF 7 * NameSpace: _11DesignPattern_ObserverDelegateTest 8 * MachineName: JIYF_PC 9 * CreateTime: 2017/5/23 20:55:58 10 * UpdatedTime: 2017/5/23 20:55:58 11 *****************************************************/ 12 using System; 13 using System.Collections.Generic; 14 using System.Linq; 15 using System.Text; 16 17 namespace _11DesignPattern_ObserverDelegateTest 18 { 19 /// <summary> 20 /// 具体的订阅博客类 21 /// </summary> 22 public class JiYFBlog : Blog 23 { 24 public JiYFBlog(string name, string blogTitile, string blogInfo) 25 : base(name, blogTitile, blogInfo) 26 { 27 28 } 29 } 30 }
订阅者类
1 /***************************************************** 2 * ProjectName: _11DesignPattern_ObserverDelegateTest 3 * Description: 4 * ClassName: Observer 5 * CLRVersion: 4.0.30319.42000 6 * Author: JiYF 7 * NameSpace: _11DesignPattern_ObserverDelegateTest 8 * MachineName: JIYF_PC 9 * CreateTime: 2017/5/23 20:56:50 10 * UpdatedTime: 2017/5/23 20:56:50 11 *****************************************************/ 12 using System; 13 using System.Collections.Generic; 14 using System.Linq; 15 using System.Text; 16 17 namespace _11DesignPattern_ObserverDelegateTest 18 { 19 /// <summary> 20 /// 具体的订阅者类 21 /// </summary> 22 public class Observer 23 { 24 /// <summary> 25 /// 订阅者名字 26 /// </summary> 27 private string m_Name; 28 public string Name 29 { 30 get { return m_Name; } 31 set { m_Name = value; } 32 } 33 34 /// <summary> 35 /// 订阅者构造函数 36 /// </summary> 37 /// <param name="name">订阅者名字</param> 38 public Observer(string name) 39 { 40 this.m_Name = name; 41 } 42 43 /// <summary> 44 /// 订阅者接受函数 45 /// </summary> 46 /// <param name="blog"></param> 47 public void Receive(object obj) 48 { 49 Blog blog = obj as Blog; 50 if (blog != null) 51 { 52 Console.WriteLine("订阅者:\"{0}\"观察到了:{1}发布的一篇博客,标题为:{2},内容为:{3}", Name, blog.BlogName, blog.BlogTitle, blog.BlogInfo); 53 } 54 } 55 } 56 }
测试代码
1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5 6 namespace _11DesignPattern_ObserverDelegateTest 7 { 8 class Client 9 { 10 static void Main(string[] args) 11 { 12 Console.WriteLine("--全部订阅者--"); 13 //创建一个JiYF的博客 14 Blog jiyfBlog = new Blog("JiYF笨小孩","丑小鸭","丑小鸭的故事"); 15 16 //创建订阅者 17 Observer obsZhangsan = new Observer("张三"); 18 Observer obsLiSi = new Observer("李四"); 19 Observer obsWangwu = new Observer("王五"); 20 21 //添加对JiYF博客的订阅者 22 jiyfBlog.AddObserver(new NotifyEventHandler(obsZhangsan.Receive)); 23 jiyfBlog.AddObserver(new NotifyEventHandler(obsLiSi.Receive)); 24 jiyfBlog.AddObserver(new NotifyEventHandler(obsWangwu.Receive)); 25 26 ////通知订阅者 27 jiyfBlog.PublishBlog(); 28 29 Console.WriteLine("---移除订阅者张三--"); 30 jiyfBlog.RemoteObserver(new NotifyEventHandler(obsZhangsan.Receive)); 31 jiyfBlog.PublishBlog(); 32 Console.ReadLine(); 33 } 34 } 35 }
运行结果：
源代码工程文件下载
