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4.观察者模式(ObserverPattern)观察者模式意图观察者模式结构观察者模式变体观察者模式效果观察者模式的实现问题例子代码classSubject{public:Subject();virtual~Subject();virtualvoidAtach(Observer*obj){observers->Append(obj);}virtualvoidDetach(Observer*obj){observers->Remove(obj);}virtualvoidNotify(){ListIterator<Observer*>i(observers);for(i.First();!i.IsDone();i.Next()){i.CurrentItem()->Update(this);}}private:List<Observer*>*observers;};//具体的目标类ClockTimerclassClockTimer:publicSubject{public:ClockTimer();virtualintGetHour();virtualintGetMinute();virtualintGetSecond();voidTick(){//记录当前时间Notify();}};//具体的观察者类DigitalClockclassDigitalClock:publicObserver{public:DigitalClock(ClockTiemr*theSubject){subject=theSubject;subject->Attach(this);}virtual~DigitalClock(){subject->Detach(this);}virtualvoidUpdate(Subject*theChangedSubject){if(theChangedSubject==subject){Draw();}}virtualvoidDraw(){inth=subject->GetHour();intm=subject->GetMinute();ints=subject->GetSecond();//绘制时钟,略}private:ClockTimer*subject;};客户代码:ClockTimer*timer=newClockTimer;AnalogClock*analogClock=newAnalogClock(timer);DigitalClock*digitalClock=newDigitalClock(timer);