设计模式发布订阅

// MyDesignPattern.cpp: 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
#include <thread>
#include <mutex>
#include <string>
#include <memory>
#include <vector>

using namespace std;


class Observer;

class Blog {
public:
    Blog() {
        std::cout << "Blog()" << std::endl;
    }

    ~Blog(void) {
        std::cout << "~Blog()" << std::endl;
    }

    void set_name(const std::string& name) {
        name_ = name;
    }
    const string get_name() {
        return name_;
    }
    void set_status(const std::string&s) {
        status_ = s;
    }
    const std::string get_status(void)const {
        return this->status_;
    }
    void add_observer(const std::shared_ptr<Observer>& pobserver)
    {
        observers_.push_back(pobserver);
    }

    void notify(void);

private:
    std::string name_;
    std::string status_;
    std::vector<std::weak_ptr<Observer>> observers_;
    typedef std::vector<std::weak_ptr<Observer>>::iterator iter;
};


class Observer
{
public:
    //由于只能指针都是值语义的，所以使用常值引用可以减少复制  
    Observer(const string& name, const std::shared_ptr<Blog>& pblog)
        :name_(name), blog_(pblog)
    {
        cout << "Observer(" << name_ << ")订阅了" << blog_.lock()->get_name() << endl;
    }
    ~Observer(void)
    {
        cout << "~Observer(" << name_ << ")" << endl;
    }
    void update(void)
    {
        std::cout << name_ << "知道了" << blog_.lock()->get_name() << blog_.lock()->get_status() << endl;
    }
private:
    string name_;

    std::weak_ptr<Blog> blog_;
};

void Blog::notify(void)
{
    iter i = observers_.begin();
    //标准写法  
    while (i != observers_.end())
    {
        //weak_ptr本身不具备访问能力（单一职责），都是通过shared_ptr来实现  
        std::shared_ptr<Observer> pobserver(i->lock());
        //判断对象是否已经析构  
        if (pobserver)
        {
            pobserver->update();
            //迭代器在这里前进  
            ++i;
        }
        //已经析构的对象不再引用  
        else
        {
            i = observers_.erase(i);
        }
    }
}




int main()
{
    std::shared_ptr<Blog> pblog(new Blog());
    pblog->set_name("CalmReason CSDN Blog");

    std::shared_ptr<Observer> pobserver1(new Observer("张三",pblog));
    std::shared_ptr<Observer> pobserver2(new Observer("李四", pblog));

    pblog->add_observer(pobserver1);
    pblog->add_observer(pobserver2);

    pblog->set_status("发表了博客:c++的内存管理");
    pblog->notify();

    pblog->set_status("发表了博客:weak_ptr的基本用法");
    pblog->notify();


    return 0;
}