设计模式：观察者模式

最新推荐文章于 2025-08-08 21:00:55 发布

转载最新推荐文章于 2025-08-08 21:00:55 发布 · 125 阅读

文章标签：

#设计 #模式 #观察者模式 #设计模式：观察者模式 #观察者 #设计模式

本文通过订报纸的例子深入浅出地介绍了观察者模式的原理及应用。观察者模式是一种行为设计模式，允许对象在状态发生变化时通知所有依赖于它的观察者对象，而无需显式调用。文中提供了C#和C++的代码实现，帮助读者更好地理解和应用此模式。

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原文地址为：设计模式：观察者模式

设计模式系列目录

今天介绍另一种模式

观察者模式是我们经常用的一个模式，比如在用wcf做服务的时候通知客户端做一些操作一般用设计者模式。

今天做一个订报纸的小例子来理解一下观察者模式出版者+订阅者=观察者模式

用下边的图来说就是人民日报+订阅者=观察者模式

只要是订阅了人民日报的人，有了新报纸就会送到订阅者那里去，

当你不想订的时候取消就不订阅就不会再收到报纸了。

下面我们就来用代码实现一下这个模式

 //报纸接口
    public interface INewsPaper
    {
        //添加订阅者
        void RegisterSubscriber(ISubScribe f_subScribe);
        //取消订阅
        void RemoveSubScriber(ISubScribe f_subScribe);
        //发送报纸
        void SendPaper();
    }

    //订阅者
    public interface ISubScribe
    {
        //有新的报纸了就会被执行通知
        void HasNewPaper();
    }

    //人民日报
    public class PeopleNewsPaper : INewsPaper
    {
        private List<ISubScribe> subList = new List<ISubScribe>();
        public void RegisterSubscriber(ISubScribe f_subScribe)
        {
            subList.Add(f_subScribe);
        }

        public void RemoveSubScriber(ISubScribe f_subScribe)
        {
            if (subList.IndexOf(f_subScribe) >= 0)
            {
                subList.Remove(f_subScribe);
            }
        }

        //发报纸啦~~
        public void SendPaper()
        {
            foreach (ISubScribe _sub in subList)
            {
                _sub.HasNewPaper();
            }
        }      
    }

    public class subHuman : ISubScribe
    {
        //订阅者的名字
        private string p_name;

        public subHuman(string f_name)
        {
            p_name = f_name;
        }
        //告诉订阅者有新报纸了
        public void HasNewPaper()
        {
            Console.WriteLine(p_name + "!! 有新的报纸了，请查收！");
        }

    }

开始订订阅，和调用了

static void Main(string[] args)
        {
            PeopleNewsPaper _paper = new PeopleNewsPaper();
            subHuman _XiaoMing = new subHuman("小明");
            subHuman _ZhaoYun = new subHuman("赵云");
            subHuman _LiuBei = new subHuman("刘备");
            //小明订报
            _paper.RegisterSubscriber(_XiaoMing);
            //赵云订报
            _paper.RegisterSubscriber(_ZhaoYun);
            //刘备订报
            _paper.RegisterSubscriber(_LiuBei);
            //有新报纸了
            _paper.SendPaper();
            Console.WriteLine("---------------发完报纸了------------------");

            //小明不想订了，取消报纸
            _paper.RemoveSubScriber(_XiaoMing);
            //又有新报纸了  就没有小明的报纸 了
            _paper.SendPaper();
            Console.ReadLine();
        }

c++代码

#pragma once
#include <iostream>

//订阅者
class ISubScribe
{
public:
//有新的报纸了就会被执行通知
virtual void HasNewPaper() = 0;

virtual ~ISubScribe(){}
};

//报纸接口
class INewsPaper
{
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 ~INewsPaper(){}
};

View Code

#pragma once
#include "inewspaper.h"
#include <iostream>
#include <vector>
using namespace std;

class PeopleNewsPaper :
public INewsPaper
{
public:
    PeopleNewsPaper();

virtual ~PeopleNewsPaper();

//添加订阅者
void RegisterSubscriber(ISubScribe* f_subScribe);
//取消订阅
void RemoveSubScriber(ISubScribe* f_subScribe);
//发送报纸
void SendPaper();

private:
    vector<ISubScribe*> subs;
};

#include "PeopleNewsPaper.h"
#include <algorithm>


void MyClearSub(ISubScribe* sub)
{
if (sub) {
        delete sub;
        sub = nullptr;
    }
}
PeopleNewsPaper::PeopleNewsPaper()
{

}


PeopleNewsPaper::~PeopleNewsPaper()
{
if (!subs.empty()) {
        for_each(subs.begin(), subs.end(), MyClearSub);
        subs.clear();
    }
}




//添加订阅者
void PeopleNewsPaper::RegisterSubscriber(ISubScribe* f_subScribe)
{
if (subs.empty()) {
        subs.push_back(f_subScribe);
    }
else if (find(subs.begin(), subs.end(), f_subScribe) == subs.end()) {
        subs.push_back(f_subScribe);
    }
}

//取消订阅
void PeopleNewsPaper::RemoveSubScriber(ISubScribe* f_subScribe)
{
    vector<ISubScribe*>::iterator itor = find(subs.begin(), subs.end(), f_subScribe);
if (itor != subs.end()) {
        subs.erase(itor);
        MyClearSub(f_subScribe);
    }
}

//发送报纸
void PeopleNewsPaper::SendPaper()
{
for (ISubScribe* sub : subs) {
        sub->HasNewPaper();
    }
}

View Code

#pragma once
#include "inewspaper.h"
#include <iostream>
#include <string>

class SubHuman :
public ISubScribe
{
public:
    SubHuman(std::string name);
~SubHuman();
void HasNewPaper();

private:
    std::string m_name;
};

#include "SubHuman.h"

using namespace std;
SubHuman::SubHuman(string name)
{
    m_name = name;
}


SubHuman::~SubHuman()
{
}

void SubHuman::HasNewPaper()
{
    std::cout << m_name << "有报纸来了！！" << endl;
}

View Code

调用

#include <iostream>
#include "inewspaper.h"
#include "PeopleNewsPaper.h"
#include "SubHuman.h"

int main()
{
    INewsPaper* peopPaper = new PeopleNewsPaper();
    ISubScribe* sub = new SubHuman("小李");
    peopPaper->RegisterSubscriber(sub);
    sub = new SubHuman("小张");
    peopPaper->RegisterSubscriber(sub);
    sub = new SubHuman("小刘");
    peopPaper->RegisterSubscriber(sub);
    peopPaper->SendPaper();
    peopPaper->RemoveSubScriber(sub);
    peopPaper->SendPaper();
    delete peopPaper;

}