.NET Delegates: A C# Bedtime Story中文版(下篇)

.NET Delegates: A C# Bedtime Story中文版(下篇)

作者：Chris Sells

译者：荣耀

【译注：C#进阶文章。Chris Sells是《ATL Internals》一书作者之一。译文中所有程序调试环境均为Microsoft Visual Studio.NET 7.0 Beta2和 Microsoft .NET Framework SDK Beta2。代码就是文章，请仔细阅读代码J】

取得所有结果

     现在，peter终于松了一口气。他已经设法满足了所有的监听者，而且不会和特定实现紧密耦合。然而，他又注意到尽管boss和universe都为工作打了分，但他只得到了一个打分。【译注：请参见上节例子代码及译注】他希望能得到每一个监听者的评分结果。因此，他决定提取委托调用列表，以便手工分别调用它们：

public void DoWork()

{

//...

Console.WriteLine("Worker: work completed");

     if( completed != null)

{

foreach( WorkCompleted wc in completed.GetInvocationList())

{

int grade = wc();

Console.WriteLine("Worker grade= " + grade);

}

}

}

【译注：以下是本节描述之完整代码示例：

using System;

delegate void WorkStarted();     

delegate void WorkProgressing();

delegate int WorkCompleted();

class Worker

{

     public void DoWork()

     {

          Console.WriteLine("Worker: work started");

          if( started != null ) started();

          Console.WriteLine("Worker: work progressing");

          if( progressing != null ) progressing();

          Console.WriteLine("Worker: work completed");

        if( completed != null)

        {

            foreach( WorkCompleted wc in completed.GetInvocationList())

            {

                int grade = wc();

                Console.WriteLine("Worker grade= " + grade);

            }

        }

     }

     public event WorkStarted started ;

     public event WorkProgressing progressing;

     public event WorkCompleted completed;

}

class Boss

{

     public int WorkCompleted()

     {

          Console.WriteLine("Better...");

         return 4; /* out of 10 */

     }

}

class Universe

{

     static void WorkerStartedWork()

     {

          Console.WriteLine("Universe notices worker starting work");

     }

     static int WorkerCompletedWork()

     {

          Console.WriteLine("Universe pleased with worker's work");

         return 7;

     }

     static void Main()

     {

         Worker peter = new Worker();

         Boss boss = new Boss();

          peter.completed += new WorkCompleted(boss.WorkCompleted);

          peter.started += new WorkStarted(Universe.WorkerStartedWork);

          peter.completed += new WorkCompleted(Universe.WorkerCompletedWork);

          peter.DoWork();

          Console.WriteLine("Main: worker completed work");

          Console.ReadLine();

     }

}

/*

以下是上段程序输出结果：

Worker: work started

Universe notices worker starting work

Worker: work progressing

Worker: work completed

Better...

Worker grade = 4 【译注：boss打的4分也得到啦J】

Universe pleased with worker's work

Worker grade = 7

Main: worker completed work

*/

】

异步通知：触发和忽略

不料，boss和universe被别的什么事纠缠上了，这就意味着他们给peter打分的时间被延迟了：

class Boss

{

public int WorkCompleted()

{

System.Threading.Thread.Sleep(3000);

             Console.WriteLine("Better...");

return 6; /* out of 10 */

}

}

class Universe

{

static int WorkerCompletedWork()

{

System.Threading.Thread.Sleep(4000);

Console.WriteLine("Universe is pleased with worker's work");

return 7;

    }

    //...

}

而不幸的是，由于peter是同时通知boss和universe并等待他们打分的，这些返回评分的通知现在看来要占用他不少工作时间，因此，peter决定忽略评分并且异步触发事件：

public void DoWork()

{

//...

Console.WriteLine("Worker: work completed");

         if( completed != null )

{

foreach( WorkCompleted wc in completed.GetInvocationList())

{

wc.BeginInvoke(null, null);

}

}

}

【译注：下面给出本节例子完整代码：

using System;

delegate void WorkStarted();     

delegate void WorkProgressing();

delegate int WorkCompleted();

class Worker

{

     public void DoWork()

     {

          Console.WriteLine("Worker: work started");

          if( started != null ) started();

          Console.WriteLine("Worker: work progressing");

          if( progressing != null ) progressing();

          Console.WriteLine("Worker: work completed");

        if( completed != null )

        {

            foreach( WorkCompleted wc in completed.GetInvocationList())

            {

                wc.BeginInvoke(null, null);

            }

        }

     }

     public event WorkStarted started ;

     public event WorkProgressing progressing;

     public event WorkCompleted completed;

}

class Boss

{

    public int WorkCompleted()

    {

        System.Threading.Thread.Sleep(3000);

        Console.WriteLine("Better...");

        return 6; /* out of 10 */

    }

}

class Universe

{

     static void WorkerStartedWork()

     {

          Console.WriteLine("Universe notices worker starting work");

     }

    static int WorkerCompletedWork()

    {

        System.Threading.Thread.Sleep(4000);

        Console.WriteLine("Universe is pleased with worker's work");

        return 7;

    }

     static void Main()

     {

         Worker peter = new Worker();

         Boss boss = new Boss();

          peter.completed += new WorkCompleted(boss.WorkCompleted);

          peter.started += new WorkStarted(Universe.WorkerStartedWork);

          peter.completed += new WorkCompleted(Universe.WorkerCompletedWork);

          peter.DoWork();

          Console.WriteLine("Main: worker completed work");

          Console.ReadLine();

     }

}

/*

以下是上段程序输出结果：

Worker: work started

Universe notices worker starting work

Worker: work progressing

Worker: work completed

Main: worker completed work //【译注：由于是异步触发事件，因此这一行先输出啦J】

Better... //【译注：评分已被忽略】

Universe pleased with worker's work //【译注：评分已被忽略】

*/

】

异步通知：轮询

     这就使得peter可以通知监听者的同时自己也能立即返回工作，让进程的线程池调用委托。然而不久他就发现监听者对其工作的评分丢掉了。【译注：请参见上节例子代码及译注】peter知道他做了一件明智的事并乐意universe作为一个整体（不单单是他的boss）评判他。因此，peter异步触发事件，但定期轮询，以察看可以获得的评分：

public void DoWork()

{

//...

Console.WriteLine("Worker: work completed");

if( completed != null )

{

foreach( WorkCompleted wc in completed.GetInvocationList() )

{

IAsyncResult res = wc.BeginInvoke(null, null);

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

int grade = wc.EndInvoke(res);

Console.WriteLine("Worker grade= " + grade);

}

}

}

【译注：下面给出本节例子完整代码：

using System;

delegate void WorkStarted();     

delegate void WorkProgressing();

delegate int WorkCompleted();

class Worker

{

     public void DoWork()

     {

          Console.WriteLine("Worker: work started");

          if( started != null ) started();

          Console.WriteLine("Worker: work progressing");

          if( progressing != null ) progressing();

          Console.WriteLine("Worker: work completed");

        if( completed != null )

        {

            foreach( WorkCompleted wc in completed.GetInvocationList() )

            {

                IAsyncResult res = wc.BeginInvoke(null, null);

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

                int grade = wc.EndInvoke(res);

                Console.WriteLine("Worker grade= " + grade);

            }

        }

     }

     public event WorkStarted started ;

     public event WorkProgressing progressing;

     public event WorkCompleted completed;

}

class Boss

{

     public int WorkCompleted()

     {

          System.Threading.Thread.Sleep(3000);

          Console.WriteLine("Better...");

         return 6; /* out of 10 */

     }

}

class Universe

{

     static void WorkerStartedWork()

     {

          Console.WriteLine("Universe notices worker starting work");

     }

     static int WorkerCompletedWork()

     {

          System.Threading.Thread.Sleep(4000);

          Console.WriteLine("Universe is pleased with worker's work");

         return 7;

     }

     static void Main()

     {

         Worker peter = new Worker();

         Boss boss = new Boss();

          peter.completed += new WorkCompleted(boss.WorkCompleted);

          peter.started += new WorkStarted(Universe.WorkerStartedWork);

          peter.completed += new WorkCompleted(Universe.WorkerCompletedWork);

          peter.DoWork();

          Console.WriteLine("Main: worker completed work");

          Console.ReadLine();

     }

}

/*

以下是上段程序输出结果：

Worker: work started

Universe notices worker starting work

Worker: work progressing

Worker: work completed

Better...

Worker grade = 6

Universe pleased with worker's work

Worker grade = 7

Main: worker completed work //【译注：注意这个结果到最后才输出，下一节首句意思即是如此】

*/

】

异步通知：委托

     不幸的是，peter又倒退了—就象他一开始想避免boss站在一旁边监视他一样。也就是说，他现在要监看整个工作过程。【译注：请参见上节示例输出结果的注释】因此，peter决定使用自己的委托作为异步委托完成时的通知方式，这样他就可以立即回去工作，而当工作被打分时，仍然可以接到通知：

public void DoWork()

{

//...

Console.WriteLine("Worker: work completed");

if( completed != null )

{

foreach( WorkCompleted wc in completed.GetInvocationList() )

{

wc.BeginInvoke(new AsyncCallback(WorkGraded), wc);

}

}

}

private void WorkGraded(IAsyncResult res)

{

WorkCompleted wc = (WorkCompleted)res.AsyncState;

int grade = wc.EndInvoke(res);

Console.WriteLine("Worker grade= " + grade);

}

【译注：下面给出本节例子完整代码：

using System;

delegate void WorkStarted();     

delegate void WorkProgressing();

delegate int WorkCompleted();

class Worker

{

     public void DoWork()

     {

          Console.WriteLine("Worker: work started");

          if( started != null ) started();

          Console.WriteLine("Worker: work progressing");

          if( progressing != null ) progressing();

          Console.WriteLine("Worker: work completed");

        if( completed != null )

        {

            foreach( WorkCompleted wc in completed.GetInvocationList() )

            {

                wc.BeginInvoke(new AsyncCallback(WorkGraded), wc);

            }

        }

     }

    private void WorkGraded(IAsyncResult res)

    {

        WorkCompleted wc = (WorkCompleted)res.AsyncState;

        int grade = wc.EndInvoke(res);

        Console.WriteLine("Worker grade= " + grade);

    }

     public event WorkStarted started ;

     public event WorkProgressing progressing;

     public event WorkCompleted completed;

}

class Boss

{

     public int WorkCompleted()

     {

          System.Threading.Thread.Sleep(3000);

          Console.WriteLine("Better...");

         return 6; /* out of 10 */

     }

}

class Universe

{

     static void WorkerStartedWork()

     {

          Console.WriteLine("Universe notices worker starting work");

     }

     static int WorkerCompletedWork()

     {

          System.Threading.Thread.Sleep(4000);

          Console.WriteLine("Universe is pleased with worker's work");

         return 7;

     }

     static void Main()

     {

         Worker peter = new Worker();

         Boss boss = new Boss();

          peter.completed += new WorkCompleted(boss.WorkCompleted);

          peter.started += new WorkStarted(Universe.WorkerStartedWork);

          peter.completed += new WorkCompleted(Universe.WorkerCompletedWork);

          peter.DoWork();

          Console.WriteLine("Main: worker completed work");

          Console.ReadLine();

     }

}

/*以下是上段程序输出结果：

Worker: work started

Universe notices worker starting work

Worker: work progressing

Worker: work completed

Main: worker completed work //【译注：异步委托发生了效果，因此这一行先输出啦J】

Better...

Worker grade = 6

Universe pleased with worker's work

Worker grade = 7

*/

】

同乐乐

     peter、boss和universe最终都满意了。boss和universe都可以仅被通知其感兴趣的事件，并减少了实现上的负担和不必要的来回调用。peter可以通知他们每一个人，而不必管需要多长时间才能从那些目标方法中返回，并仍然可以异步得到评分结果。peter知道做到这一点并不太容易，因为由于是异步触发事件，目标方法就有可能运行在另一个线程里，就如上节示例一样。不过，peter[J]和mike[J]是好朋友，而mike精通线程问题并可提供该领域的指导。

     从此，他们都很快乐J

－全文完－