观察者模式

来源：互联网发布：算法第四版英文版pdf 编辑：程序博客网时间：2024/05/29 19:15

#include <iostream>#include <string>#include <list>using namespace std;class Subject;class Observer{protected:    string name;    Subject *sub;public:    Observer(string name,Subject *sub)    {        this->name=name;        this->sub=sub;    }    virtual void update()=0;};class StockObserver:public Observer{public:    StockObserver(string name,Subject *sub):Observer(name,sub)    {    }    void update();};class NBAObserver:public Observer{public:    NBAObserver(string name,Subject *sub):Observer(name,sub)    {    }    void update();};class Subject{protected:    list<Observer*> observers;public:    string action;    virtual void attach(Observer*)=0;    virtual void detach(Observer*)=0;    virtual void notify()=0;};class Secretary:public Subject{    void attach(Observer *observer)    {        observers.push_back(observer);    }    void detach(Observer *observer)    {        list<Observer *>::iterator iter=observers.begin();        while(iter!=observers.end())        {            if((*iter)==observer)            {                observers.erase(iter);            }            ++iter;        }    }    void notify()    {        list<Observer *>::iterator iter=observers.begin();        while(iter!=observers.end())        {            (*iter)->update();            ++iter;        }    }};void StockObserver::update(){    cout<<name<<" 收到消息："<<sub->action<<endl;    if(sub->action=="梁所长来了!")    {        cout<<"我马上关闭股票，装做很认真工作的样子！"<<endl;    }}void NBAObserver::update(){    cout<<name<<" 收到消息："<<sub->action<<endl;    if(sub->action=="梁所长来了!")    {        cout<<"我马上关闭NBA，装做很认真工作的样子！"<<endl;    }}int main(){    Subject *dwq=new Secretary();    Observer *xs=new NBAObserver("xiaoshuai",dwq);    Observer *zy=new NBAObserver("zouyue",dwq);    Observer *lm=new StockObserver("limin",dwq);    dwq->attach(xs);    dwq->attach(zy);    dwq->attach(lm);    dwq->action="去吃饭了！";    dwq->notify();    cout<<endl;    dwq->action="梁所长来了!";    dwq->notify();    return 0;}

GOOD：定义了一种一对多的关系，让多个观察对象（公司员工）同时监听一个主题对象（秘书），主题对象状态发生变化时，会通知所有的观察者，使它们能够更新自己。

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