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】 类型耦合 从前，在南方的一个异国他乡，有一个叫peter的勤劳的工人。他对boss百依百顺，但他 的boss却是个卑鄙无信的小人，他坚持要求peter不断汇报工作情况。由于peter不希望 被boss盯着干活，于是他向boss承诺随时汇报工作进度。peter利用类型引用定期回调b oss来实现这个承诺： using system;//【译注：译者补充】 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不关心. */ } public void workprogressing() { /*boss不关心. */ } 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(); } } /*【译注：以下是上段程序输出结果： worker: work started worker: work progressing worker: work completed it's about time! worker grade = 2 main: worker completed work 】*/ 接口 现在，peter成了一个特殊人物，他不但能够忍受卑鄙的boss，和universe也建立 了紧密的联系。peter感到universe对他的工作进程同样感兴趣。不幸的是，除了保证b oss能够被通知外，如果不为universe添加一个特殊的通知方法和回调，peter无法向un iverse通知其工作进程。peter希望能从那些通知方法的实现中分离出潜在的通知约定， 为此，他决定将方法剥离到接口中： using system; //【译注：译者补充】 interface iworkerevents //【译注：这就是分离出来的接口】 { void workstarted(); void workprogressing(); int workcompleted(); } class worker { public void advise(iworkerevents events) //【译注：现在传递的参数类型为 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 //【译注：boss实现该接口】 { public void workstarted(){ /*boss不关心. */ } public void workprogressing(){ /*boss不关心. */ } 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); //【译注：或peter.advise((iworkerevents)boss); 】 peter.dowork(); console.writeline("main: worker completed work"); console.readline(); } } /*【译注：以下是上段程序输出结果： 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实现这个接口，以至于没有顾得上通知univer se也实现该接口，但他知道不久就需如此，至少，他已经抽象了对boss的引用，因此， 别的实现了iworkerevents接口的什么人都可以收到工作进度通知。【译注：请参见上一 节代码示例及译注】 然而，peter的boss依然极度不满，“peter！”boss咆哮者，“你为什么要通知我 什么时候开始工作、什么时候正在进行工作？我不关心这些事件，你不但强迫我实现这 些方法，你还浪费了你的宝贵的工作时间等我从事件中返回。当我实现的方法需占用很 长时间时，你等我的时间也要大大延长！你难道不能想想别的办法不要老是来烦我吗？ ” 此时，peter意识到尽管在很多情况下接口很有用，但在处理事件时，接口的粒度 还不够精细。他还要能做到仅仅通知监听者真正感兴趣的事件。因此，peter决定把接口 里的方法肢解成若干个独立的委托函数，每一个都好象是只有一个方法的小接口。 using system; //【译注：译者补充】 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; //【译注：这样写更规矩：public workstarted started = null;】 public workprogressing progressing; //【译注：这样写更规矩：public work progressing progressing = null;】 public workcompleted completed; //【译注：这样写更规矩：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(); } } /*【译注：以下是上段程序输出结果： worker: work started worker: work progressing worker: work completed better... worker grade = 4 main: worker completed work 】 */ 【译注：对“但在处理事件时，接口的粒度还不够精细”的理解可用下例说明，请仔细 观察一下程序，思考一下这样做的不利之处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(); } } /*以下是上段程序输出结果： worker: work completed better... worker grade = 4 main: worker completed work */ 】 静态监听者 这就达到了不用boss不关心的事件去烦他的目标。但是，peter还是不能够使univ erse成为其监听者。因为universe是一个全封闭的实体，所以将委托挂钩在universe的 实例上不妥的（设想一下universe的多个实例需要多少资源...）。peter意识到应将委 托挂钩于universe的静态成员上，因为委托也完全适应于静态成员： 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 */ } } //【译注：以上代码为译者补充】 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); //【译注：× 】 peter.started = new workstarted(universe.workerstartedwork); peter.completed = new workcompleted(universe.workercompletedwork);// 【译注：这一行代码使得“×”那一行代码白做了l】 peter.dowork(); console.writeline("main: worker completed work"); console.readline(); } } /*【译注：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 universe pleased with worker's work worker grade = 7 main: worker completed work 】*/ 事件 不幸的是，universe现在变得太忙并且不习惯于注意某一个人—universe用自己的 委托取代了peter的boss的委托，这显然是将worker类的委托字段设为public的意外的副 作用。【译注：请参见上节例子代码及译注】同样地，如果peter的boss不耐烦了，他自 己就可以触发peter的委托（peter的boss可是有暴力倾向的） // peter的boss自己动手了 if( peter.completed != null ) peter.completed(); peter希望确保不会发生这两种情况。他意识到必须为每一个委托加入注册和反注册函数 ，这样监听者就可以添加或移去它们，但谁都不能够清空整个事件列表。peter自己没去 实现这些方法，相反，他使用event关键字让c#编译器帮他达到这个目的： class worker { //... public event workstarted started; public event workprogressing progressing; public event workcompleted completed; } peter懂得关键字event使得委托具有这样的特性：只允许c#客户用+=或-=操作符添 加或移去它们自己，这样就迫使boss和universe举止文雅一些： 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(); } 【译注：以下是完整代码： 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 ) { 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); //【译注： √】 peter.started += new workstarted(universe.workerstartedwork); peter.completed += new workcompleted(universe.workercompletedwork); peter.dowork(); console.writeline("main: worker completed work"); console.readline(); } } /*
以下是上段程序输出结果： worker: work started universe notices worker starting work worker: work progressing worker: work completed better...// 【译注：boss也通知到啦j“√”那一行代码有用啦j，但是且慢，boss打 的那4分没有得到，后面只得到了universe给的7分l】 universe pleased with worker's work worker grade = 7 main: worker completed work */ 】
