明辉手游网中心:是一个免费提供流行视频软件教程、在线学习分享的学习平台!

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

[摘要]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 St...
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