观察者模式

1、概念

所谓观察，就是一个多个对象【观察者】观察一个对象【被观察者】，当被观察者有什么行为时会触发所有观察者，观察者根据自己的实际情况完成对应的操作【观察者通常有一个虚基类，实现其接口】。

2、例子：老公回家前发消息，妻子开始做饭，孩子停止玩游戏

#include <iostream>
#include <vector>
#include <algorithm>
#include <memory>
class ObserverInterface{
public:
    virtual void dosomething()=0;
    virtual ~ObserverInterface(){}
};

class SubjectInterface{
public:
    virtual void Add(ObserverInterface* obr)=0;
    virtual void Remove(ObserverInterface* obr)=0;
    virtual void Notify()=0;

    virtual ~SubjectInterface(){}
};

class Me:public SubjectInterface{
public:
    void Add(ObserverInterface* obr) override{
        observers.push_back(obr);
    }

    void Remove(ObserverInterface* obr) override{
        auto pos=std::find(observers.begin(),observers.end(),obr);
        if(pos!=observers.end()){
            observers.erase(pos);
        }
    }

    void Notify() override{
        for(const auto& obs:observers){
            obs->dosomething();
        }
    }

private:
    std::vector<ObserverInterface*> observers;
};

class Wife:public ObserverInterface{
public:
    ~Wife(){std::cout << "wife relax"<<std::endl;}
    void dosomething() override{
        std::cout<<"start cooking"<<std::endl;
    }
};

class Son:public  ObserverInterface{
public:
    ~Son(){std::cout << "son relax"<<std::endl;}
    void dosomething() override {
        std::cout<<"stop gaming"<<std::endl;
    }
};

int main(){
    Me me;
    ObserverInterface* wife=new Wife;
    ObserverInterface* son=new Son;
    me.Add(wife);
    me.Add(son);

    //下班了 发消息
    me.Notify();

    delete wife;
    delete son;
}

3、使用智能指针管理观察者

#include <iostream>
#include <vector>
#include <algorithm>
#include <memory>

class ObserverInterface {
public:
    ~ObserverInterface(){std::cout << "ObserverInterface relax"<<std::endl;}
    virtual void dosomething()=0;
    virtual ~ObserverInterface(){}
};

using pObserverInterface=std::shared_ptr<ObserverInterface>;
class SubjectInterface{
public:
    virtual void Add(pObserverInterface obr)=0;
    virtual void Remove(pObserverInterface obr)=0;
    virtual void Notify()=0;
};


class Me : public SubjectInterface{
public:
    void Add(pObserverInterface obr) override{
        observers.push_back(obr);
    }

    void Remove(pObserverInterface obr) override{
        auto pos=std::find(observers.begin(),observers.end(),obr);
        if(pos!=observers.end()){
            observers.erase(pos);
        }
    }

    void Notify() override{
        for(const auto& obs:observers){
            obs->dosomething();
        }
    }

private:
    std::vector<pObserverInterface> observers;
};


class Wife : public ObserverInterface{
public:
    ~Wife(){std::cout << "wife relax"<<std::endl;}
    void dosomething() override{
        std::cout<<"start cooking"<<std::endl;
    }

};

class Son : public ObserverInterface{
public:
    ~Son(){std::cout << "son relax"<<std::endl;}
    void dosomething() override {
        std::cout<<"stop gaming"<<std::endl;
    }
};


int main(){
    Me me;
    auto wife = std::make_shared<Wife>();
    auto son = std::make_shared<Son>();
    me.Add(wife);
    me.Add(son);
    //下班了 发消息
    me.Notify();

}

Ps：Qt的信号与槽就是一个观察者模式，信号产生，让连接了的槽都去执行。