观察者模式【C++版】

一、定义观察者类

   a)观察者基类

enum ObservedStatus {Dining, Sleeping, Working};
/*******************************定义多个观察者类*************************************/

//定义观察者的父类(抽象类,实际作用相当于java中的接口)
class Observer
{
 public:
   virtual void update(ObservedStatus status)=0;
   virtual ~Observer() {}//保证父类指针指向子类时,delete基类指针,子类的析构行为能正确调用
};

   b)具体观察者类

class DiningObserver: public Observer
{
     void update(ObservedStatus status)//只需要实现观察者父类中update虚函数
    {
       if (status == Dining) {
           cout<<"我是观察者DiningObserver,当前被观察者的状态为：Dining!"<<endl;
       }else{
           cout<<"我是观察者DiningObserver,但状态不匹配"<<endl;
       }
    }
};


class SleepingObserver: public Observer
{
     void update(ObservedStatus status)//只需要实现观察者父类中update虚函数
    {
       if (status == Sleeping) {
           cout<<"我是观察者SleepingObserver,当前被观察者的状态为：Sleeping!"<<endl;
       }else{
           cout<<"我是观察者SleepingObserver,但状态不匹配"<<endl;
       }
    }
};


class WorkingObserver: public Observer
{
     void update(ObservedStatus status)//只需要实现观察者父类中update虚函数
    {
       if (status == Working) {
           cout<<"我是观察者WorkingObserver,当前被观察者的状态为：Working!"<<endl;
       }else{
           cout<<"我是观察者WorkingObserver,但状态不匹配"<<endl;
       }
    }
};

二、定义被观察者类

 a)被观察者基类

/*******************************定义被观察者类*************************************/

class ObservedBase//被观察者基类
{
  public:
       virtual void addObserver(Observer *observer)=0;//添加观察者
       virtual void removeObserver(Observer *observer)=0;//删除观察者
       virtual void notifyToObservers()=0;//将自身信息通知观察者
};

 b)实际被观察者类

class Observed:public ObservedBase
{ 
   public:

        Observed(ObservedStatus _status)//构造函数
        {
          status=_status;
        }
        
        void addObserver(Observer *observer)//添加某个观察者
        {
          observersList.push_back(observer);
        }

        void removeObserver(Observer *observer)//移除某个观察者
        {
          observersList.remove(observer);
        }

        void notifyToObservers()//通知所有观察者
        {
            for (list<Observer*>::iterator it = observersList.begin(); 
             it!= observersList.end(); ++it) 
            { 
               Observer* theObserver = *it;
               theObserver->update(status); 
            }  
        }
  private: 
     list<Observer*>  observersList; 
     ObservedStatus status;
};

三、主函数调用

int main()
{
 cout<<"测试程序:"<<endl;
 Observer *FirstObserver=new DiningObserver();
 Observer *SecondObserver=new SleepingObserver();
 Observer *ThirdObserver=new WorkingObserver();

 Observed *myObserved=new Observed(Working);
 myObserved->addObserver(FirstObserver);
 myObserved->addObserver(SecondObserver);
 myObserved->addObserver(ThirdObserver);

 myObserved->notifyToObservers();//通知所有观察者

 cout<<endl;
 cout<<"从列表中移除观察者SleepingObserver后再通知："<<endl<<endl;
 myObserved->removeObserver(SecondObserver);//移除第二个观察者SleepingObserver
 myObserved->notifyToObservers();//通知所有观察者

 delete FirstObserver;
 delete SecondObserver;
 delete ThirdObserver;
 system("pause");
 return 0;
}

 运行结果：