c++观察者模式

1.观察者模式简介

   观察者模式（Observer），又叫发布-订阅模式（Publish/Subscribe），定义对象间一种一对多的依赖关系，使得每当一个对象改变状态，则所有依赖于它的对象都会得到通知并自动更新。

2.源码实现

#include <iostream>
#include <string>
#include <list>

using namespace std;

class Observer
{
public:
    virtual void Update(int) = 0;
};

class Subject
{
public:
    virtual void Attach(Observer *) = 0;
    virtual void Detach(Observer *) = 0;
    virtual void Notify() = 0;
};

class ConcreteObserver : public Observer
{
public:
    ConcreteObserver(Subject *pSubject) : m_pSubject(pSubject){};

    void Update(int value)
    {
        cout << "ConcreteObserver get the update New State: " << value << endl;
    }

private:
    Subject *m_pSubject;
};

class ConcreteObserver2 : public Observer
{
public:
    ConcreteObserver2(Subject *pSubject) : m_pSubject(pSubject){};

    void Update(int value)
    {
        cout << "ConcreteObserver2 get the update New State: " << value << endl;
    }

private:
    Subject *m_pSubject;
};

class ConcreteSubject : public Subject
{
public:
    void Attach(Observer *pObserver)
    {
        m_ObserverList.push_back(pObserver);
    }

    void Detach(Observer *pObserver)
    {
        m_ObserverList.remove(pObserver);
    }

    void Notify()
    {
        list<Observer *>::iterator it = m_ObserverList.begin();

        while(it != m_ObserverList.end())
        {
            (*it)->Update(m_iState);
            it++;
        };
    }

    void SetState(int state)
    {
        m_iState = state;
    }

private:
    list<Observer *> m_ObserverList;
    int m_iState;
};

int main(int argc, char **argv)
{
    ConcreteSubject *pSubject = new ConcreteSubject();

    Observer *pObserver = new ConcreteObserver(pSubject);
    Observer *pObserver2 = new ConcreteObserver2(pSubject);

    pSubject->SetState(2);
    pSubject->Attach(pObserver);
    pSubject->Attach(pObserver2);

    pSubject->Notify();

    pSubject->Detach(pObserver);
    pSubject->SetState(3);
    pSubject->Notify();

    delete pObserver;
    delete pObserver2;
    delete pSubject;

    return 0;
}

3.编译源码

$ g++ -o example example.cpp

4.运行及其结果

$ ./example
ConcreteObserver get the update New State: 2
ConcreteObserver2 get the update New State: 2
ConcreteObserver2 get the update New State: 3