设计模式-观察者模式

观察者模式又称订阅-发布模式。指程序中有一个主题（subject），有若干个观察者（observer）；当主题发生变动时，主题将通知订阅了该主题的观察者（调用观察者的updata方法）。程序可在运行时动态的添加或删除观察者。

讨论模型：
学校为主题，学生为观察者，学校将向学生发布三个数据。每次数据更新时，注册成为观察者的学生都会收到变化的数据。并可以在运行时，动态的添加删除观察者（学生）。

subject基类：

//subject.h#ifndef _________Subject__#define _________Subject__#include <stdio.h>#include "Observer.h"class Subject{public:    virtual void registerObserver(Observer* observer)=0;//添加观察者    virtual void removeObserver(Observer* observer)=0;//删除观察者    virtual void notifyObservers()=0;//数据变动时subject调用此方法通知observer进行updata};#endif

observer基类

//observer.h#ifndef _________Observer__#define _________Observer__#include <stdio.h>#include "map"#include "string"class Observer{public:    virtual void updata(std::map<std::string, int> data)=0;//调用该方法更新数据，参数为map类型键值对，可根据实际情况修改或重载};#endif

继承自subject的school类

//school.h#ifndef _________school__#define _________school__#include <stdio.h>#include "Subject.h"#include "Observer.h"#include <random>#include "vector"#include "map"class school : public Subject {private:    int data1;//三个数据    int data2;    int data3;    std::vector<Observer*> Obs;//观察者向量    std::map<std::string, int> data;//储存三组数据的mappublic:    school() = default;    void getData(){        data1 = random();//更新三组数据        data2 = random();        data3 = random();        data["data1"] = data1;        data["data2"] = data2;        data["data3"] = data3;        notifyObservers();//调用notifyObserves通知observes调用updata    }    void registerObserver(Observer* observer){        Obs.push_back(observer);//将参数observer加入观察者列表    }    void removeObserver(Observer* observer){        for (auto i = Obs.begin(); i!=Obs.end(); i++) {            if (*i == observer) {                Obs.erase(i);//在列表中删除指定的observer            }        }    };    void notifyObservers(){        for (auto i = Obs.begin(); i!=Obs.end(); i++) {            (*i)->updata(data);//通知所有observer进行updata        }    }};#endif

继承自observer的student类

//student.h#ifndef _________student__#define _________student__#include <stdio.h>#include "Observer.h"class students : public Observer{private:    int data1;    int data2;    int data3;    int studentNum;public:    students(int studentNum){        this->studentNum = studentNum;    }    void updata(std::map<std::string, int> data){        data1 = data["data1"];        data2 = data["data2"];        data3 = data["data3"];        show();    }    void show(){        printf("student number:%d    data1:%d,data2:%d,data3:%d\n",studentNum,data1,data2,data3);    }};#endif

主函数：

#include <iostream>#include "school.h"#include "student.h"int main(int argc, const char * argv[]) {    auto sch  = new school();    auto stu1 = new students(1);    auto stu2 = new students(2);    auto stu3 = new students(3);    sch->registerObserver(stu1);    sch->registerObserver(stu2);    sch->registerObserver(stu3);    sch->getData();    sch->removeObserver(stu2);    sch->getData();    sch->removeObserver(stu1);    sch->getData();    sch->registerObserver(stu1);    sch->getData();    return 0;}

输出结果

student number:1    data1:1804289383,data2:846930886,data3:1681692777student number:2    data1:1804289383,data2:846930886,data3:1681692777student number:3    data1:1804289383,data2:846930886,data3:1681692777student number:1    data1:1714636915,data2:1957747793,data3:424238335student number:3    data1:1714636915,data2:1957747793,data3:424238335student number:3    data1:719885386,data2:1649760492,data3:596516649student number:3    data1:1189641421,data2:1025202362,data3:1350490027student number:1    data1:1189641421,data2:1025202362,data3:1350490027