[设计模式]-观察者模式应用

来源：互联网发布：数据割接流程编辑：程序博客网时间：2024/05/22 05:06

1.观察者模式的概念

观察者模式我们可以想象报纸提供商和报纸订阅者的关系，一个报纸提供商持有一个列表，列表记录着若干个报纸订阅者，每次报纸印刷出来之后，报纸提供商要通知订阅者来取报纸。如果新增一个订阅者，下一次就能被通知到。如果某个订阅者不再订阅，下一次就不再通知该订阅者。

2.观察者模式的例子

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace ObservePatternDemo{    class NewsPaperReader    {        public string Name;        public NewsPaperReader(string name)        {            this.Name = name;        }        public void ReadNewsPaper(NewsPaper newsPaper)        {            Console.WriteLine(this.Name +" is reading Newspaer,date is: " + newsPaper.Date + ",title is: " + newsPaper.Title);        }    }    class NewsPaper    {        public string Date;        public string Title;        public NewsPaper(string date,string title)        {            this.Date = date;            this.Title = title;        }    }    class NewsPaperProvider    {        private readonly List<NewsPaperReader> readers = new List<NewsPaperReader>();        public void AddReader(NewsPaperReader reader)        {            if(!readers.Contains(reader))                readers.Add(reader);        }        public void RemoveReader(NewsPaperReader reader)        {            if (readers.Contains(reader))                readers.Remove(reader);        }        public void NotifyAll()        {            var newsPaper = new NewsPaper("2014-11-14", "Good News");            foreach (NewsPaperReader reader in readers)            {                reader.ReadNewsPaper(newsPaper);            }        }    }    class Program    {        static void Main(string[] args)        {            var newsPaperProvider = new NewsPaperProvider();            var readerA = new NewsPaperReader("ReaderA");            var readerB = new NewsPaperReader("ReaderB");            newsPaperProvider.AddReader(readerA);            newsPaperProvider.AddReader(readerB);            newsPaperProvider.NotifyAll();            newsPaperProvider.RemoveReader(readerB);            newsPaperProvider.NotifyAll();            Console.ReadKey();        }    }}

上述观察者模式的例子比较简单，就不画UML图了。

观察者模式的精髓在于发布者持有一个List，里面有订阅者的名单。每次通知的时候，根据订阅者列表，逐一调用通知方法。这种情形非常类似责任链模式，即一个处理的Manager持有一个处理方法的List，针对一个对象依次进行处理。示例如下：

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace ObservePatternDemo2{    /// <summary>    /// Helper interface    /// </summary>    interface IHelper    {        void DoWork();    }    /// <summary>    /// Build process    /// </summary>    class BuildHelper : IHelper    {        public void DoWork()        {            Console.WriteLine("Build is starting...");        }    }    /// <summary>    /// Deploy helper    /// </summary>    class DeployHelper : IHelper    {        public void DoWork()        {            Console.WriteLine("Deploy is starting...");        }    }    /// <summary>    /// Instal helper    /// </summary>    class InstallHelper : IHelper    {        public void DoWork()        {            Console.WriteLine("Install is starting...");        }    }    /// <summary>    /// Test helper    /// </summary>    class TestHelper : IHelper    {        public void DoWork()        {            Console.WriteLine("Test is starting...");        }    }    /// <summary>    /// Uninstall helper    /// </summary>    class UninstallHelper : IHelper    {        public void DoWork()        {            Console.WriteLine("Uninstall is starting...");        }    }        class HelperProvider    {        private List<IHelper> helpers = new List<IHelper>();        public HelperProvider()        {        }        public HelperProvider(List<IHelper> helpers)        {            this.helpers = helpers;        }        public void AddReader(IHelper helper)        {            if (!helpers.Contains(helper))                helpers.Add(helper);        }        public void RemoveReader(IHelper helper)        {            if (helpers.Contains(helper))                helpers.Remove(helper);        }        public void DoProcess()        {            foreach (IHelper helper in helpers)            {                helper.DoWork();            }        }    }    class Program    {        static void Main(string[] args)        {            var helpers = new List<IHelper>            {                new BuildHelper(),                new DeployHelper(),                new InstallHelper(),                new TestHelper(),                new UninstallHelper()            };            var helperProvider = new HelperProvider(helpers);            helperProvider.DoProcess();                        Console.ReadKey();        }    }}

运行结果：

总结：模式并非一成不变，观察者模式灵活运用一下就可以做成责任链模式，类似工作流的处理，灵活运用，事半功倍！

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