观察者模式

观察者模式，也称发布订阅模式，主题方发布，观察方订阅。

observe.h

/*
 *
 * Copyright (C) 2023-09-13 14:06 zxinlog <[email protected]>
 *
 */
#include <func.h>

#include <iostream>
#include <list>
using std::cout;
using std::endl;
using std::list;

class Observe {
public:
    virtual void update(int status) = 0;
};

class Subject {
public:
    virtual void attach(Observe *obs) = 0;
    virtual void detach(Observe *obs) = 0;
    virtual void notify() = 0;
    virtual void setStatus(int status) = 0;
    virtual int getStatus() = 0;
};

class ConcretSubject : public Subject {
public:
    void attach(Observe *obs);
    void detach(Observe *obs);
    void notify();
    void setStatus(int status);
    int getStatus();

private:
    list<Observe *> _list;
    int _status;
};

class ObserveA : public Observe {
    void update(int status);
};

class ObserveB : public Observe {
    void update(int status);
};

class ObserveC : public Observe {
    void update(int status);
};

observe.cc

/*
 *
 * Copyright (C) 2023-09-13 14:11 zxinlog <[email protected]>
 *
 */
#include <func.h>

#include <iostream>
#include <memory>

#include "observe.h"
using std::cout;
using std::endl;
using std::shared_ptr;

void ConcretSubject::attach(Observe *obs) {
    _list.push_back(obs);
}

void ConcretSubject::detach(Observe *obs) {
    for (auto i = _list.begin(); i != _list.end(); i++) {
        if (*i == obs) {
            _list.remove(obs);
            return;
        }
    }
}

void ConcretSubject::notify() {
    for (std::list<Observe *>::iterator i = _list.begin(); i != _list.end(); i++) {
        (*i)->update(_status);
    }
}

void ConcretSubject::setStatus(int status) {
    _status = status;
}

int ConcretSubject::getStatus() {
    return _status;
}

void ObserveA::update(int status) {
    cout << "Observe-A"
         << " observe status is " << status << endl;
}
void ObserveB::update(int status) {
    cout << "Observe-B"
         << " observe status is " << status << endl;
}

void ObserveC::update(int status) {
    cout << "Observe-C"
         << " observe status is " << status << endl;
}

// test
int main() {
    shared_ptr<Subject> sub(new ConcretSubject());
    shared_ptr<Observe> obA(new ObserveA());
    shared_ptr<Observe> obB(new ObserveB());
    shared_ptr<Observe> obC(new ObserveC());

    sub->setStatus(1);
    sub->attach(obA.get());
    sub->attach(obB.get());
    sub->attach(obC.get());
    sub->notify();

    sub->detach(obB.get());
    sub->setStatus(3);
    sub->notify();
}

使用list存储观察者队列信息。
使用attach添加观察者
使用detach删除观察者
使用notify通知观察者更新。