观察者模式 observer

Observer是一种1对多的模式

Subject类用来通知 Observer类用来响应通知

 

Subject类内部有一个Observer类的指针链表 每当Subject类消息被触发时 遍历该链表来调用Observer类的响应

 

Obesrver模式的实现要点是,

第一一般subject类都是采用链表等容器来存放Observer对象,

第二抽取出Observer对象的一些公共的属性形成Observer基类,而Subject中保存的则是Observer类对象的指针,这样就使Subject和具体的Observer实现了解耦

 

具体实现

#ifndef _OBSERVER_ #define _OBSERVER_ #include <list> class Observer; class Subject { public: Subject(); ~Subject(); void Notify(); void Attach(Observer* pOb); void Detach(Observer* pOb); private: std::list<Observer*> m_list; }; class Observer { public: Observer(){}; ~Observer(){}; virtual void Update() = 0; }; class ObserverCar : public Observer { public: ObserverCar(){}; ~ObserverCar(){}; virtual void Update(); }; class ObserverBus : public Observer { public: ObserverBus(){}; ~ObserverBus(){}; virtual void Update(); }; #endif

 

#include "stdafx.h" #include "Observer.h" Subject::Subject() { m_list.empty(); } Subject::~Subject() { m_list.empty(); } void Subject::Attach(Observer* pOb) { m_list.push_back(pOb); } void Subject::Detach(Observer* pOb) { std::list<Observer*>::iterator iter; for(iter = m_list.begin(); iter != m_list.end(); iter++) { if((*iter) == pOb) m_list.erase(iter); } } void Subject::Notify() { if(m_list.empty()) return; std::list<Observer*>::iterator iter; for(iter = m_list.begin(); iter != m_list.end(); iter++) { (*iter)->Update(); } } void ObserverCar::Update() { printf("Update car/n"); } void ObserverBus::Update() { printf("Update bus/n"); } int _tmain(int argc, _TCHAR* argv[]) { Subject* pSub = new Subject(); Observer* pCar = new ObserverCar(); Observer* pBus = new ObserverBus(); pSub->Attach(pCar); pSub->Attach(pBus); pSub->Notify(); delete pSub; delete pCar; delete pBus; return 0; }