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Delegate比较全面的例子(原创)

Posted on 2005-02-02 01:28 idior 阅读(...) 评论(...)  编辑 收藏

将Delegate理解为接口,只有一个方法的接口,这样最容易理解。这个方法只有声明,没有实现,实现在别的类。(实际上应该把它看作函数指针,不过接口更容易理解些。)

在你的类中有一个Delegate就相当于有一个接口。通过这个接口你可以调用一个方法,而这个方法在别的类定义,由别的类来干。

为了说的形象一点,举个例子:

学生考试完后成绩出来了,考的好了老师要表扬,考的不好了老师要批评。

 

使用接口的方法:


using
System;
 

public class Student

{

     private IAdviser adviser;

 

     public void SetAdviser(IAdviser iadviser)

     {

         adviser = iadviser;

     }

 

     private int score;

 

     public void SetScore(int value)

     {

         if (value > 100 || value < 0)

         {

              Console.Out.WriteLine("分数不对");

         }

         else

         {

              score = value;

              if (adviser != null)

              {

                   string result = adviser.Advise(score);

                   Console.Out.WriteLine("学生收到老师返回的结果\t"+result);

              }

         }

     }

 }

public
interface IAdviser

{

     string Advise(int score);

}

 

public class Teacher : IAdviser

{

     public string Advise(int score)

     {

         if (score < 60)

         {

              Console.Out.WriteLine(score+"老师说加油");

              return "不及格";

         }

         else

         {

              Console.Out.WriteLine(score+"老师说不错");

              return "及格";

         }

     }

 

 

}

 

class MainClass

{

     [STAThread]

     private static void Main(string[] args)

     {

         IAdviser teacher = new Teacher();

         Student s = new Student();

         s.SetAdviser(teacher);

 

         Console.Out.WriteLine("学生得到50");

         s.SetScore(50);

 

         Console.Out.WriteLine("\n学生得到75");

         s.SetScore(75);

 

         Console.ReadLine();

     }

}

 

使用Delegate的方法:

using System;

using System.Threading;

 

public class Student

{

 

     private int score;

 

     public void SetScore(int value)

     {

         if (value > 100 || value < 0)

         {

              Console.Out.WriteLine("分数不对");

         }

         else

         {

              score = value;

              if (AdviseDelegateInstance!= null)

              {

                   string result=AdviseDelegateInstance(score);

                   Console.Out.WriteLine("学生收到老师返回的结果\t"+result);

              }

         }

     }

 

     public  delegate string AdviseDelegate(int score);

        

     public AdviseDelegate AdviseDelegateInstance;

}

 

public class Teacher

{

     public string Advise(int score)

     {

         if(score<60)

         {

              Console.Out.WriteLine(score+"老师说加油");

              return "不及格";

         }

         else

         {

              Console.Out.WriteLine(score+"老师说不错");

              return "及格";

         }

     }

}

 

class MainClass

{

     [STAThread]

     static void Main(string[] args)

     {

         Teacher teacher=new Teacher();

         Student s=new Student();

 

         s.AdviseDelegateInstance=new Student.AdviseDelegate(teacher.Advise);

        

         Console.Out.WriteLine("学生得到50");

         s.SetScore(50);

 

         Console.Out.WriteLine("\n学生得到75");

         s.SetScore(75);

 

         Console.ReadLine();

     }

}


如果老师很忙不能及时回复怎么办?比如这样:

public class Teacher

{

     public string Advise(int score)

     {

         Thread.Sleep(3000);

         if(score<60)

         {

              Console.Out.WriteLine(score+"老师说加油");

              return "不及格";

         }

         else

         {

              Console.Out.WriteLine(score+"老师说不错");

              return "及格";

         }

     }

}
总不能让学生一直等下去吧,采用多线程并发的办法。
Interface的解决办法: 
     public void SetScore(int value)

     {

         if (value > 100 || value < 0)

         {

              Console.Out.WriteLine("分数不对");

         }

         else

         {

              score = value;

              if (adviser != null)

              {

                   Thread.adviserThread=new Thread(new ThreadStart(adviser.Advise()));

                   adviserThread.Start();

              }

         }

     }


但是它不能使用带参数的函数,怎么办?(谁知道方法请指教)
.Net2.0提供了新的方法ParameterizedThreadStart


Delegate解决(异步调用):

     public void SetScore(int value)

     {

         if (value > 100 || value < 0)

         {

              Console.Out.WriteLine("分数不对");

         }

         else

         {

              score = value;

              if (AdviseDelegateInstance!= null)

              {

                     AdviseDelegateInstance.BeginInvoke(score,null,null);                    

              }

         }

     }

不过这样我们失去了老师的返回结果,不知道有没有及格了。

采用轮讯的方法去获得结果:

     public void SetScore(int value)

     {

         if (value > 100 || value < 0)

         {

              Console.Out.WriteLine("分数不对");

         }

         else

         {

              score = value;

              if (AdviseDelegateInstance!= null)

              {

 

                       IAsyncResult res = AdviseDelegateInstance.BeginInvoke(score,null, null);

 

                       while( !res.IsCompleted ) System.Threading.Thread.Sleep(1);

 

                       string result = AdviseDelegateInstance.EndInvoke(res);

                       Console.Out.WriteLine("学生收到老师返回的结果\t"+result);

                  

              }

         }

     }

 

不过这样主线程又被阻塞了,采用回调的方式: (注:接口也可以采用回调的方式获得返回值)

     public void SetScore(int value)

     {

         if (value > 100 || value < 0)

         {

              Console.Out.WriteLine("分数不对");

         }

         else

         {

              score = value;

              if (AdviseDelegateInstance!= null)

              {

                   IAsyncResult res = AdviseDelegateInstance.BeginInvoke(score, new System.AsyncCallback(CallBackMethod), null);

              }

         }

     }

 

     private void CallBackMethod(IAsyncResult asyncResult)

     {  

         string result = AdviseDelegateInstance.EndInvoke(asyncResult);

 

         Console.Out.WriteLine("学生收到老师返回的结果\t" + result);

     }


这样就比较得到了一个比较好的解决方案了。我们再来看看BeginInvoke的第四个参数是干吗的呢?


    
public void SetScore(int value)

     {

         if (value > 100 || value < 0)

         {

              Console.Out.WriteLine("分数不对");

         }

         else

         {

              score = value;

              if (AdviseDelegateInstance!= null)

              {

                   AdviseDelegateInstance.BeginInvoke(score, new System.AsyncCallback(CallBackMethod), "idior");

              }

         }

     }

 

     private void CallBackMethod(IAsyncResult asyncResult)

     {

         string result = AdviseDelegateInstance.EndInvoke(asyncResult);

         string stateObj=(string)asyncResult.AsyncState;

 

         Console.Out.WriteLine("学生{0}收到老师返回的结果\t" + result,stateObj.ToString());

     }

 

哦,原来它可以用来标记调用者的一些信息。(这里采取的是硬编码的方式,你可以把它改为学生的id之类的信息)。


总结:Delegate类似与Interface但是功能更加强大和灵活,它甚至还可以绑定到Static方法只要函数签名一致,而且由于+=操作符的功能,实现多播也是极为方便(即Observer模式),在此不再举例。

(补充:多播的时候改一下SetScore函数)

     public void SetScore(int value)

     {

         if (value > 100 || value < 0)

         {

              Console.Out.WriteLine("分数不对");

         }

         else

         {

              score = value;

             

              if (AdviseDelegateInstance!= null)

              {

                   foreach( AdviseDelegate ad in AdviseDelegateInstance.GetInvocationList())

                   {

                       ad.BeginInvoke(score, new System.AsyncCallback(CallBackMethod), "idior");

                   }

              }

         }

     }

 

本文没什么新的内容,就是自己练一下手,写个总结材料,希望对大家有帮助。.net2.0提供了更好的线程模型。

 

完整源代码如下:

  

 

using System;

using System.Threading;

 

public class Student

{

     private int score;

 

 

     public void SetScore(int value)

     {

         if (value > 100 || value < 0)

         {

              Console.Out.WriteLine("分数不对");

         }

         else

         {

              score = value;

              if (AdviseDelegateInstance!= null)

              {

                   AdviseDelegateInstance.BeginInvoke(score, new System.AsyncCallback(CallBackMethod), "idior");

              }

         }

     }

 

     private void CallBackMethod(IAsyncResult asyncResult)

     {

         string result = AdviseDelegateInstance.EndInvoke(asyncResult);

         string stateObj=(string)asyncResult.AsyncState;

 

         Console.Out.WriteLine("学生{0}收到老师返回的结果\t" + result,stateObj);

     }

 

    

 

     public delegate string AdviseDelegate(int score);

 

     public AdviseDelegate AdviseDelegateInstance;

 

 

}

 

public class Teacher

{

     public string Advise(int score)

     {

         Thread.Sleep(3000);

         if (score < 60)

         {

              Console.Out.WriteLine(score + "老师说加油");

              return "不及格";

         }

         else

         {

              Console.Out.WriteLine(score + "老师说不错");

              return "及格";

         }

     }

}

 

class MainClass

{

     [STAThread]

     private static void Main(string[] args)

     {

         Teacher teacher = new Teacher();

         Student s = new Student();

 

         s.AdviseDelegateInstance= new Student.AdviseDelegate(teacher.Advise);

 

         Console.Out.WriteLine("学生得到50");

         s.SetScore(50);

 

         Console.Out.WriteLine("\n学生得到75");

         s.SetScore(75);

 

 

         Console.ReadLine();

     }

}

参考资料: .NET Delegates: A C# Bedtime Story