#Observer成就系统achievements system玩家完成某种成就后,通知监督者,监督者做出相应出来```//简单来说就是事件触发的时候, 通知监督者class Observer{public:  virtual ~Observer() {}  virtual void onNotify(const Entity& entity, Event event) = 0;};class Achievements : public Observer{public:  virtual void onNotify(const Entity& entity, Event event)  {    switch (event)    {    case EVENT_ENTITY_FELL:      if (entity.isHero() && heroIsOnBridge_)      {        unlock(ACHIEVEMENT_FELL_OFF_BRIDGE);      }      break;      // Handle other events, and update heroIsOnBridge_...    }  }private:  void unlock(Achievement achievement)  {    // Unlock if not already unlocked...  }  bool heroIsOnBridge_;};class Subject{private:  Observer* observers_[MAX_OBSERVERS];  int numObservers_;   public:  void addObserver(Observer* observer)  {    // Add to array...  }  void removeObserver(Observer* observer)  {    // Remove from array...  }    protected:  void notify(const Entity& entity, Event event)  {    for (int i = 0; i < numObservers_; i++)    {      observers_[i]->onNotify(entity, event);    }  }    };```语言绑定:        java mvc    c# event其他例子:```1 ui得到数据改变的通知2 数据改变,ui即时表现出来```