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

时间:2006/7/19 6:57:21 作者:佚名 人气:32

.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-
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