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(qǐng)仔細(xì)閱讀代碼j】 類型耦合 從前，在南方的一個(gè)異國(guó)他鄉(xiāng)，有一個(gè)叫peter的勤勞的工人。他對(duì)boss百依百順，但他 的boss卻是個(gè)卑鄙無(wú)信的小人，他堅(jiān)持要求peter不斷匯報(bào)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(shí)匯報(bào)工作進(jìn)度。peter利用類型引用定期回調(diào)b oss來(lái)實(shí)現(xiàn)這個(gè)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(gè)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(duì)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(gè)特殊的通知方法和回調(diào)，peter無(wú)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(shí)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(lái)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(shí)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(shí)現(xiàn)這個(gè)接口，以至于沒有顧得上通知univer se也實(shí)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(duì)boss的引用，因此， 別的實(shí)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(qǐng)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(shí)候開始工作、什么時(shí)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(shí)現(xiàn)這 些方法，你還浪費(fèi)了你的寶貴的工作時(shí)間等我從事件中返回。當(dāng)我實(shí)現(xiàn)的方法需占用很 長(zhǎng)時(shí)間時(shí)，你等我的時(shí)間也要大大延長(zhǎng)！你難道不能想想別的辦法不要老是來(lái)煩我嗎？ ” 此時(shí)，peter意識(shí)到盡管在很多情況下接口很有用，但在處理事件時(shí)，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(gè)獨(dú)立的委托函數(shù)，每一個(gè)都好象是只有一個(gè)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() { worker peter = 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(duì)“但在處理事件時(shí)，接口的粒度還不夠精細(xì)”的理解可用下例說(shuō)明，請(qǐng)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?yàn)閡niverse是一個(gè)全封閉的實(shí)體，所以將委托掛鉤在universe的 實(shí)例上不妥的（設(shè)想一下universe的多個(gè)實(shí)例需要多少資源...）。peter意識(shí)到應(yīng)將委 托掛鉤于universe的靜態(tài)成員上，因?yàn)槲幸餐耆m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(gè)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(qǐng)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(dòng)手了 if( peter.completed != null ) peter.completed(); peter希望確保不會(huì)發(fā)生這兩種情況。他意識(shí)到必須為每一個(gè)委托加入注冊(cè)和反注冊(cè)函數(shù) ，這樣監(jiān)聽者就可以添加或移去它們，但誰(shuí)都不能夠清空整個(gè)事件列表。peter自己沒去 實(shí)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(gè)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 */ 】
