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

編輯：關於C語言

【譯注：C#進階文章。Chris Sells是《ATL Internals》一書作者之一。譯文中所有程
序調試環境均為Microsoft Visual Studio.NET 7.0 Beta2和 Microsoft .Net Framewo
rk SDK Beta2。代碼就是文章，請仔細閱讀代碼J】
取得所有結果
     現在，peter終於松了一口氣。他已經設法滿足了所有的監聽者，而且不會和特定
實現緊密耦合。然而，他又注意到盡管boss和universe都為工作打了分，但他只得到了
一個打分。【譯注：請參見上節例子代碼及譯注】他希望能得到每一個監聽者的評分結
果。因此，他決定提取委托調用列表，以便手工分別調用它們：
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);
}
}
}
【譯注：以下是本節描述之完整代碼示例：
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();
     }
}
/*
以下是上段程序輸出結果：
Worker: work started
Universe notices worker starting work
Worker: work progressing
Worker: work completed
Better...
Worker grade = 4 【譯注：boss打的4分也得到啦J】
Universe pleased with worker's work
Worker grade = 7
Main: worker completed work
*/
】
異步通知：觸發和忽略
不料，boss和universe被別的什麼事糾纏上了，這就意味著他們給peter打分的時間被延
遲了：
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，由於peter是同時通知boss和universe並等待他們打分的，這些返回評分的
通知現在看來要占用他不少工作時間，因此，peter決定忽略評分並且異步觸發事件：
public void DoWork()
{
//...
Console.WriteLine("Worker: work completed");
         if( completed != null )
{
foreach( WorkCompleted wc in completed.GetInvocationList())
{
wc.BeginInvoke(null, null);
}
}
}
【譯注：下面給出本節例子完整代碼：
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();
     }
}
/*
以下是上段程序輸出結果：
Worker: work started
Universe notices worker starting work
Worker: work progressing
Worker: work completed
Main: worker completed work //【譯注：由於是異步觸發事件，因此這一行先輸出啦
J】
Better... //【譯注：評分已被忽略】
Universe pleased with worker's work //【譯注：評分已被忽略】
*/
】
異步通知：輪詢
     這就使得peter可以通知監聽者的同時自己也能立即返回工作，讓進程的線程池調
用委托。然而不久他就發現監聽者對其工作的評分丟掉了。【譯注：請參見上節例子代
碼及譯注】peter知道他做了一件明智的事並樂意universe作為一個整體（不單單是他的
boss）評判他。因此，peter異步觸發事件，但定期輪詢，以察看可以獲得的評分：
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);
}
}
}
【譯注：下面給出本節例子完整代碼：
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();
     }
}
/*
以下是上段程序輸出結果：
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 //【譯注：注意這個結果到最後才輸出，下一節首句意
思即是如此】
*/
】
異步通知：委托
     不幸的是，peter又倒退了—就象他一開始想避免boss站在一旁邊監視他一樣。也
就是說，他現在要監看整個工作過程。【譯注：請參見上節示例輸出結果的注釋】因此
，peter決定使用自己的委托作為異步委托完成時的通知方式，這樣他就可以立即回去工
作，而當工作被打分時，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);
}
【譯注：下面給出本節例子完整代碼：
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();
     }
}
/*以下是上段程序輸出結果：
Worker: work started
Universe notices worker starting work
Worker: work progressing
Worker: work completed
Main: worker completed work //【譯注：異步委托發生了效果，因此這一行先輸出啦
J】
Better...
Worker grade = 6
Universe pleased with worker's work
Worker grade = 7
*/
】
同樂樂
     peter、boss和universe最終都滿意了。boss和universe都可以僅被通知其感興趣
的事件，並減少了實現上的負擔和不必要的來回調用。peter可以通知他們每一個人，而
不必管需要多長時間才能從那些目標方法中返回，並仍然可以異步得到評分結果。pete
r知道做到這一點並不太容易，因為由於是異步觸發事件，目標方法就有可能運行在另一
個線程裡，就如上節示例一樣。不過，peter[J]和mike[J]是好朋友，而mike精通線程問
題並可提供該領域的指導。
     從此，他們都很快樂J
－全文完－