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作者：Chris Sells
譯者：榮耀
【譯注：C#進(jìn)階文章。Chris Sells是《ATL Internals》一書作者之一。譯文中所有程
序調(diào)試環(huán)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(xì)閱讀代碼J】
類型耦合
從前，在南方的一個異國他鄉(xiāng)，有一個叫peter的勤勞的工人。他對boss百依百順，但他
的boss卻是個卑鄙無信的小人，他堅持要求peter不斷匯報工作情況。由于peter不希望
被boss盯著干活，于是他向boss承諾隨時匯報工作進(jìn)度。peter利用類型引用定期回調(diào)b
oss來實現(xiàn)這個承諾：
using System;//【譯注：譯者補(bǔ)充】
class Worker
{
public void Advise(Boss boss)
{
_boss = boss;
}
public void DoWork()
{
Console.WriteLine("Worker: work started");
if( _boss != null ) _boss.WorkStarted();
Console.WriteLine("Worker: work progressing");
if( _boss != null ) _boss.WorkProgressing();
Console.WriteLine("Worker: work completed");
if( _boss != null )
{
int grade = _boss.WorkCompleted();
Console.WriteLine("Worker grade = " + grade);
}
}
private Boss _boss;
}
class Boss
{
public void WorkStarted() { /*boss不關(guān)心. */ }
public void WorkProgressing() { /*boss不關(guān)心. */ }
public int WorkCompleted()
{
Console.WriteLine("It's about time!");
return 2; /* out of 10 */
}
}
class Universe
{
static void Main()
{
Worker peter = new Worker();
Boss boss = new Boss();
peter.Advise(boss);
peter.DoWork();
Console.WriteLine("Main: worker completed work");
Console.ReadLine();
}
}
/*【譯注：以下是上段程序輸出結(jié)果：
Worker: work started
Worker: work progressing
Worker: work completed
It's about time!
Worker grade = 2
Main: worker completed work
】*/
接口
現(xiàn)在，peter成了一個特殊人物，他不但能夠忍受卑鄙的boss，和universe也建立
了緊密的聯(lián)系。peter感到universe對他的工作進(jìn)程同樣感興趣。不幸的是，除了保證b
oss能夠被通知外，如果不為universe添加一個特殊的通知方法和回調(diào)，peter無法向un
iverse通知其工作進(jìn)程。Peter希望能從那些通知方法的實現(xiàn)中分離出潛在的通知約定，
為此，他決定將方法剝離到接口中：
using System; //【譯注：譯者補(bǔ)充】
interface IWorkerEvents //【譯注：這就是分離出來的接口】
{
void WorkStarted();
void WorkProgressing();
int WorkCompleted();
}
class Worker
{
public void Advise(IWorkerEvents events) //【譯注：現(xiàn)在傳遞的參數(shù)類型為
接口引用】
{
_events = events;
}
public void DoWork()
{
Console.WriteLine("Worker: work started");
if( _events != null ) _events.WorkStarted();
Console.WriteLine("Worker: work progressing");
if(_events != null ) _events.WorkProgressing();
Console.WriteLine("Worker: work completed");
if(_events != null )
{
int grade = _events.WorkCompleted();
Console.WriteLine("Worker grade = " + grade);
}
}
private IWorkerEvents _events;
}
class Boss : IWorkerEvents //【譯注：Boss實現(xiàn)該接口】
{
public void WorkStarted(){ /*boss不關(guān)心. */ }
public void WorkProgressing(){ /*boss不關(guān)心. */ }
public int WorkCompleted()
{
Console.WriteLine("It's about time!");
return 3; /* out of 10 */
}
}
class Universe
{
static void Main()
{
Worker peter = new Worker();
Boss boss = new Boss();
peter.Advise(boss); //【譯注：或peter.Advise((IWorkerEvents)boss);
】
peter.DoWork();
Console.WriteLine("Main: worker completed work");
Console.ReadLine();
}
}
/*【譯注：以下是上段程序輸出結(jié)果：
Worker: work started
Worker: work progressing
Worker: work completed
It's about time!
Worker grade = 3
Main: worker completed work
】*/
委托
不幸的是，由于peter忙于通知boss實現(xiàn)這個接口，以至于沒有顧得上通知univer
se也實現(xiàn)該接口，但他知道不久就需如此，至少，他已經(jīng)抽象了對boss的引用，因此，
別的實現(xiàn)了IworkerEvents接口的什么人都可以收到工作進(jìn)度通知。【譯注：請參見上一
節(jié)代碼示例及譯注】
然而，peter的boss依然極度不滿，“Peter！”boss咆哮者，“你為什么要通知我
什么時候開始工作、什么時候正在進(jìn)行工作？我不關(guān)心這些事件，你不但強(qiáng)迫我實現(xiàn)這
些方法，你還浪費了你的寶貴的工作時間等我從事件中返回。當(dāng)我實現(xiàn)的方法需占用很
長時間時，你等我的時間也要大大延長！你難道不能想想別的辦法不要老是來煩我嗎？
”
此時，peter意識到盡管在很多情況下接口很有用，但在處理事件時，接口的粒度
還不夠精細(xì)。他還要能做到僅僅通知監(jiān)聽者真正感興趣的事件。因此，peter決定把接口
里的方法肢解成若干個獨立的委托函數(shù)，每一個都好象是只有一個方法的小接口。
using System; //【譯注：譯者補(bǔ)充】
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 )
{
int grade = completed();
Console.WriteLine("Worker grade = " + grade);
}
}
public WorkStarted started; //【譯注：這樣寫更規(guī)矩：public WorkStarted
started = null;】
public WorkProgressing progressing; //【譯注：這樣寫更規(guī)矩：public Work
Progressing progressing = null;】
public WorkCompleted completed; //【譯注：這樣寫更規(guī)矩：public WorkComp
leted completed = null;】
}
class Boss
{
public int WorkCompleted()
{
Console.WriteLine("Better...");
return 4; /* out of 10 */
}
}
class Universe
{
static void Main()
{
Workerpeter = new Worker();
Boss boss = new Boss();
peter.completed = new WorkCompleted(boss.WorkCompleted);
peter.DoWork();
Console.WriteLine("Main: worker completed work");
Console.ReadLine();
}
}
/*【譯注：以下是上段程序輸出結(jié)果：
Worker: work started
Worker: work progressing
Worker: work completed
Better...
Worker grade = 4
Main: worker completed work
】
*/
【譯注：對“但在處理事件時，接口的粒度還不夠精細(xì)”的理解可用下例說明，請仔細(xì)
觀察一下程序，思考一下這樣做的不利之處J
using System;
interface IWorkStartedEvent
{
void WorkStarted();
}
interface IWorkProgressingEvent
{
void WorkProgressing();
}
interface IWorkCompletedEvent
{
int WorkCompleted();
}
class Worker
{
public void Advise(IWorkCompletedEvent AEvent)
{
_event = AEvent;
}
public void DoWork()
{
Console.WriteLine("Worker: work completed");
if(_event != null )
{
int grade = _event.WorkCompleted();
Console.WriteLine("Worker grade = " + grade);
}
}
private IWorkCompletedEvent _event;
}
class Boss : IWorkCompletedEvent
{
public int WorkCompleted()
{
Console.WriteLine("Better...");
return 4; /* out of 10 */
}
}
class Universe
{
static void Main()
{
Worker peter = new Worker();
Boss boss = new Boss();
peter.Advise(boss);
peter.DoWork();
Console.WriteLine("Main: worker completed work");
Console.ReadLine();
}
}
/*以下是上段程序輸出結(jié)果：
Worker: work completed
Better...
Worker grade = 4
Main: worker completed work
*/
】
靜態(tài)監(jiān)聽者
這就達(dá)到了不用boss不關(guān)心的事件去煩他的目標(biāo)。但是，peter還是不能夠使univ
erse成為其監(jiān)聽者。因為universe是一個全封閉的實體，所以將委托掛鉤在universe的
實例上不妥的（設(shè)想一下Universe的多個實例需要多少資源...）。peter意識到應(yīng)將委
托掛鉤于universe的靜態(tài)成員上，因為委托也完全適應(yīng)于靜態(tài)成員：
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 )
{
int grade = completed();
Console.WriteLine("Worker grade= " + grade);
}
}
public WorkStarted started = null;
public WorkProgressing progressing = null;
public WorkCompleted completed = null;
}
class Boss
{
public int WorkCompleted()
{
Console.WriteLine("Better...");
return 4; /* out of 10 */
}
}
//【譯注：以上代碼為譯者補(bǔ)充】
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); //【譯注：×
】
peter.started = new WorkStarted(Universe.WorkerStartedWork);
peter.completed = new WorkCompleted(Universe.WorkerCompletedWork);//
【譯注：這一行代碼使得“×”那一行代碼白做了L】
peter.DoWork();
Console.WriteLine("Main: worker completed work");
Console.ReadLine();
}
}
/*【譯注：以下是上段程序輸出結(jié)果：
Worker: work started
Universe notices worker starting work
Worker: work progressing
Worker: work completed
Universe pleased with worker's work
Worker grade = 7
Main: worker completed work
】*/
事件
不幸的是，universe現(xiàn)在變得太忙并且不習(xí)慣于注意某一個人—universe用自己的
委托取代了peter的boss的委托，這顯然是將Worker類的委托字段設(shè)為public的意外的副
作用。【譯注：請參見上節(jié)例子代碼及譯注】同樣地，如果peter的boss不耐煩了，他自
己就可以觸發(fā)peter的委托（peter的boss可是有暴力傾向的）
// peter的boss自己動手了
if( peter.completed != null ) peter.completed();
peter希望確保不會發(fā)生這兩種情況。他意識到必須為每一個委托加入注冊和反注冊函數(shù)
，這樣監(jiān)聽者就可以添加或移去它們，但誰都不能夠清空整個事件列表。peter自己沒去
實現(xiàn)這些方法，相反，他使用event關(guān)鍵字讓C#編譯器幫他達(dá)到這個目的：
class Worker
{
//...
public event WorkStarted started;
public event WorkProgressing progressing;
public event WorkCompleted completed;
}
peter懂得關(guān)鍵字event使得委托具有這樣的特性：只允許C#客戶用+=或-=操作符添
加或移去它們自己，這樣就迫使boss和universe舉止文雅一些：
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();
}
【譯注：以下是完整代碼：
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 )
{
int grade = completed();
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); //【譯注：
√】
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(jié)果：
Worker: work started
Universe notices worker starting work
Worker: work progressing
Worker: work completed
Better...// 【譯注：boss也通知到啦J“√”那一行代碼有用啦J，但是且慢，boss打
的那4分沒有得到，后面只得到了Universe給的7分L】
Universe pleased with worker's work
Worker grade = 7
Main: worker completed work
*/ <>
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