10 观察者模式

老板回来，我不知道——观察者模式

观察者模式，又叫发布-订阅（Publish/Subscribe）模式，定义了一种一对多的依赖关系，让多个观察者对象同时监听某一个主题对象。这个主体对象在状态发生变化时，会通知所有观察者对象，使它们能够自动更新自己。

“当一个对象的改变需要同时改变其他对象时使用此模式。”

“而且它不知道具体有多少对象有待改变时，应该考虑使用观察者模式。”
“总的来讲，观察者模式所作的工作其实就是在解除耦合。让耦合的双方都依赖于抽象而不是依赖于具体。从而使得各自的变换都不会影响另一边的变化。”

//main.cpp
 #include "Boss.h"
#include "Observer.h"
#include "StockObserver.h"
#include "Subject.h"
#include "NBAObserver.h"

 int main()
{
    //老板胡汉三
     Boss *huhansan = new Boss();

    //看股票的同事
    StockObserver *tongshi1 = new StockObserver("小魏", huhansan);
    //看NBA的同事
    NBAObserver *tongshi2 = new NBAObserver("小易", huhansan);

    huhansan->Attach(tongshi1);
    huhansan->Attach(tongshi2);

    huhansan->Detach(tongshi1);

    //老板回来
    huhansan->action = "我胡汉三回来了！";
    //发出通知
    huhansan->Notify();

    return 0;
};

//Subject.h
#include <string>

using namespace std;

class Observer;

#ifndef SUBJECT_H_H
#define SUBJECT_H_H

class Subject
{
public:
    virtual void Attach(Observer *observer){}
    virtual void Detach(Observer *observer){}
    virtual void Notify(){}
public:
    string action;
};

#endif

//Boss.h
#include <list>
#include "Subject.h"
using namespace std;

class Observer;

#ifndef BOSS_H_H
#define BOSS_H_H

class Boss : public Subject
{
public:
    void Attach(Observer *observer);
    void Detach(Observer *observer);
    void Notify();

private:
    list<Observer*> observers; //此处保存的是指针
    
};

#endif

//Observer.h
#include <string>
using namespace std;

class Subject;

#ifndef OBSERVER_H_H
#define OBSERVER_H_H

//抽象的观察者
class Observer
{
public:
    Observer(){}
    Observer(string name, Subject *sub);
    virtual void Update(){}

public:
    string name;
    Subject *sub;

};

#endif

//StockObserver.h
#include "Observer.h"

class Observer;

#ifndef STOCKOBSERVER_H_H
#define STOCKOBSERVER_H_H

//看股票的同事
class StockObserver : public Observer
{
public:
    StockObserver(string name, Subject *sub);
    virtual void Update();
};

#endif

//NBAObserver.h
#include "Observer.h"

class Observer;

#ifndef NBAOBSERVER_H_H
#define NBAOBSERVER_H_H

//看股票的同事
class NBAObserver : public Observer
{
public:
    NBAObserver(string name, Subject *sub);
    virtual void Update();
};

#endif

//Observer.cpp
#include "observer.h"
#include "Subject.h"

Observer::Observer(string name, Subject *sub)
{
    this->name = name;
    this->sub = sub;
}

//Boss.cpp
#include "boss.h"
#include "observer.h"
#include <iostream>
using namespace std;

void Boss::Attach(Observer *observer)
{
    observers.push_back(observer);
}

void Boss::Detach(Observer *observer)
{
    for(list<Observer*>::iterator iter = observers.begin(); iter != observers.end(); ++iter)
    {
        if((*iter)->name == observer->name)
        {
            observers.erase(iter);
            break;
        }
    }
}

void Boss::Notify()
{
    cout<<action<<endl;
    for(list<Observer*>::iterator iter = observers.begin(); iter != observers.end(); ++iter)
    {
        (*iter)->Update();//通知所有观察者更新状态
    }
}

//StockObserver.cpp
#include "stockobserver.h"
#include "Observer.h"
#include "Subject.h"

#include <iostream>

using namespace std;

StockObserver::StockObserver(string name, Subject *sub)
{
    Observer(name, sub);
    //this->name = name;
    //this->sub = sub;
}

void StockObserver::Update()
{
    //cout<<sub->action<<" "<<name<<" 关闭股票行情，继续工作！"<<endl;
    cout<<name<<" 关闭股票行情，继续工作！"<<endl;
}

//NBAObserver.cpp
#include "nbaobserver.h"
#include "Observer.h"
#include "Subject.h"

#include <iostream>

NBAObserver::NBAObserver(string name, Subject *sub)
{
    Observer(name, sub);
    //this->name = name;
    //this->sub = sub;
}

void NBAObserver::Update()
{
    //cout<<sub->action<<" "<<name<<" 关闭NBA直播，继续工作！"<<endl;
    cout<<name<<" 关闭NBA直播，继续工作！"<<endl;
}