观察者模式

1、观察者模式简介

  观察者模式也叫发布-订阅模式、模型-视图模式、源-监听器模式以及从属者模式，观察者模式定义了对象之间的一对多依赖关系，使得每当一个对象状态发生改变时，其相关依赖对象皆得到通知并被自动更新。

2、实例讲解

  假如张三、李四、王五三人都订阅了环球日报的报纸。那么当环球日报的报纸有更新的时候就会送到他们三人手中。

//报纸接口类
class NewsPaperBase
{
public:
    //添加订阅者
    virtual void RegisterSubscriber(ISubScribe* f_subScribe) = 0;
    //取消订阅
    virtual void RemoveSubScriber(ISubScribe* f_subScribe) = 0;
    //发送报纸
    virtual void SendPaper() = 0;

    virtual ~NewsPaperBase(){}
};

//订阅者接口类
class SubScribeBase
{
public:
    //有新的报纸了就会被执行通知
    virtual void HasNewPaper() = 0;
	virtual string GetName();
    virtual ~SubScribeBase(){}
	
};

//具体实现是哪种报纸
class GlobalDaily :
    public NewsPaperBase
{
public:
    GlobalDaily();
    virtual ~GlobalDaily();
   //重写基类方法
    void RegisterSubscriber(SubScribeBase* f_subScribe)
	{
		subs.add(f_subScribe);//伪代码
		cout << f_subScribe->GetName().c_str()<<"完成订阅" << endl;
	}
     void RemoveSubScriber(SubScribeBase* f_subScribe)
	 {
		subs.remove(f_subScribe);//伪代码
		cout << f_subScribe->GetName().c_str()<<"取消订阅" << endl;
	 }
    void SendPaper()
	{
		for(auto v:subs)
		{
			v->HasNewPaper();
		}
	}

private:
	//关联订阅者
    vector<SubScribeBase*> subs;
};

//具体的订阅者实现
class SubPeople :
    public SubScribeBase
{
public:
    SubPeople(std::string name):m_name(name){};
    ~SubPeople();
    void HasNewPaper()
	{
		std::cout << m_name << "收到报纸" << endl;
	}
	string GetName()
	{
		return m_name;
	}
private:
    std::string m_name;
};

//调用步骤
int main()
{
    NewsPaperBase* pGlobalPaper = new GlobalDaily();
    SubScribeBase* sub = new SubPeople("张三");
    pGlobalPaper->RegisterSubscriber(sub);
    sub = new SubPeople("李四");
    pGlobalPaper->RegisterSubscriber(sub);
    sub = new SubPeople("王五");
    pGlobalPaper->RegisterSubscriber(sub);
    pGlobalPaper->SendPaper();
    
  	return 0;

}