.NET Delegates: A C# Bedtime Story中文版(下篇)轉
2024-07-10 13:02:17
供稿：網友
作者：chris sells
譯者：榮耀
【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終于松了一口氣。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被別的什么事糾纏上了，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，由于peter是同時通知boss和universe并等待他們打分的，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決定忽略評分并且異步觸發事件：
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：由于是異步觸發事件，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并樂意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：注意這個結果到最后才輸出，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，并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，并仍然可以異步得到評分結果。pete
r知道做到這一點并不太容易，因為由于是異步觸發事件，目標方法就有可能運行在另一
個線程里，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
題并可提供該領域的指導。
從此，他們都很快樂j
－全文完－
