C++ 设计模式： 观察者模式

#ifndef H_OBSERVER_H
#define H_OBSERVER_H


#include <iostream>
#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);
    void Detach(Observer* pObserver);
    void Notify();

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

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

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

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

void ConcreteSubject::Notify()
{
    std::list<Observer*>::iterator it = m_ObserverList.begin();
    while (it != m_ObserverList.end())
    {
        (*it)->Update(m_iState);
        ++it;
    }
}

int pf()
{
    // Create Subject
    ConcreteSubject* pSubject = new ConcreteSubject();

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

    // Change the state
    pSubject->SetState(2);

    // Register the observer
    pSubject->Attach(pObserver);
    pSubject->Attach(pObserver2);

    pSubject->Notify();

    // Unregister the observer
    pSubject->Detach(pObserver);

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

    delete pObserver;
    delete pObserver2;
    delete pSubject;
}

#endif // !H_OBSERVER_H