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

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 Framewo
rk 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。pete
r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－