.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－
