观察者模式

1.定义

在GOF的《设计模式:可复用面向对象软件的基础》一书中对观察者模式是这样说的：定义对象间的一种一对多的依赖关系，当一个对象的状态发生改变时，所有依赖于它的对象都得到通知并被自动更新。

2.代码简单实现

#include<iostream>
#include<string>
#include<list>
using namespace std;
class AbObserver
{
public:
    virtual void getMessage(string message) = 0;
};

class AbSecretary
{
public:
    virtual void sendMessage(string message) = 0;
    virtual void addObserver(AbObserver * observer) = 0;
};
//开小差的同事类（观察者）
class Observer:public AbObserver
{
public:
    void getMessage(string message)
    {
        cout << message << endl;
    }
};
//秘书类（主题对象，通知者）
class Secretary:public AbSecretary
{
public:
    void sendMessage(string message)
    {
        for (list<AbObserver *>::iterator it = observers.begin(); it != observers.end(); it++)
        {
            (*it)->getMessage(message);
        }
    }
    void addObserver(AbObserver * observer)
    {
        observers.push_back(observer);
    }
private:
    list<AbObserver *> observers;
};

int main()
{
    Observer *observer1 = new Observer;
    Observer *observer2 = new Observer;
    Secretary * secretary = new Secretary;
    secretary->addObserver(observer1);
    secretary->addObserver(observer2);
    secretary->sendMessage("老板来了");
    secretary->sendMessage("老板走了");
    system("pause");
    return 0;
}