观察者模式C++

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当对象间存在一对多的关系，当状态改变时，其他对象都得到通知，这就是观察者模式了。

观察者模式实现发布-订阅功能。如我们有个项目叫NGI，需要召开StanUp会议，会议上需求变更时需要通过所有参加会议的人员，我们就可以使用观察者模式，其UML图如下：

其代码实现如下：

#include <iostream>
#include <list>
#include <string>
using namespace std;

class Observer
{
public:
    Observer(){}
    virtual ~Observer(){}
    virtual void Update(){}
};

class Meeting
{
private:
    list<Observer*> m_obser;
protected:
    string  m_state;
public:
    Meeting(){}
    virtual ~Meeting(){}
    void Attach(Observer* obser)
    {
        m_obser.push_back(obser);
    }

    void Remove(Observer* pObser)
    {
        m_obser.remove(pObser);
    }

    void Notify()
    {
        list<Observer*>::iterator iter;
        for (iter = m_obser.begin(); iter != m_obser.end(); iter++)
        {
            (*iter)->Update();
        }
    }

    virtual void SetStatus(string s) { m_state = s; }
    virtual string GetStatus(void) { return m_state; }
};

class StanUpMeeting : public Meeting
{
private:
    string m_name;
public:
    StanUpMeeting(string name) :m_name(name) {}
    ~StanUpMeeting(){}
    void SetStatus(string s) { m_state = "StanUp Meeting Notify ：" + m_name + s; }
    string GetStatus() { return m_state; }
};

class NgiObserver :public Observer
{
private:
    string m_name;
    Meeting* m_meeting;
public:
    NgiObserver(string name, Meeting* meeting):m_name(name), m_meeting(meeting){}
    ~NgiObserver() {}
    void Update()
    {
        string status = m_meeting->GetStatus();
        cout << m_name << "******" << status << endl;
    }
};

int main(int argc, char** argv)
{
    Meeting *meeting = new StanUpMeeting("PM:");
    Observer *observer = new NgiObserver("Clark", meeting);
    meeting->Attach(observer);
    meeting->SetStatus("NGI Projrct requirment changed");
    meeting->Notify();

    delete meeting; delete observer;

    return 0;
}

以上代码在VS2015上运行通过。