.NET Delegates: A C# Bedtime Story中文版(下篇)转
2024-07-10 13:02:17
供稿：网友
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－
