Observer模式-白红宇

Observer模式

阅读量：4133 次

发布时间：2019-05-25

本文共 3515 字，大约阅读时间需要 11 分钟。

Observer模式要解决的问题：建立一个一（Subject）对多（Observer）的依赖关系，当“一”变化的时候，依赖这个“一”的多也能够同步改变

Subject.h

//Subject.h#ifndef _SUBJECT_H_#define _SUBJECT_H_#include 
   
    #include 
    
     using namespace std;typedef string State;class Observer;class Subject{public:	virtual ~Subject();	virtual void Attach(Observer* obv);	virtual void Detach(Observer* obv);	virtual void Notify();	virtual void SetState(const State& st) = 0;	virtual State GetState() = 0;protected:	Subject();private:	list
     
      * _obvs;};class ConcreteSubject:public Subject{public:	ConcreteSubject();	~ConcreteSubject();	State GetState();	void SetState(const State& st);protected:private:	State _st;};#endif //~_SUBJECT_H_

Subject.cpp

#include "Subject.h"#include "Observer.h"#include 
   
    #include 
    
     using namespace std;typedef string state;Subject::Subject(){ //在模板的使用之前一定要new，创建	_obvs = new list
     
      ;}Subject::~Subject(){ }void Subject::Attach(Observer* obv){	_obvs->push_front(obv);}void Subject::Detach(Observer* obv){	if (obv != NULL)		_obvs->remove(obv);}void Subject::Notify(){	list
      
       ::iterator it;	it = _obvs->begin();	for (;it != _obvs->end();it++)	{ //关于模板和iterator的用法		(*it)->Update(this);	}}ConcreteSubject::ConcreteSubject(){	_st = '\0';}ConcreteSubject::~ConcreteSubject(){ }State ConcreteSubject::GetState(){	return _st;}void ConcreteSubject::SetState(const State& st){	_st = st;}

Observer.h

//Observer.h#ifndef _OBSERVER_H_#define _OBSERVER_H_#include "Subject.h"#include 
   
    using namespace std;typedef string State;class Observer{public:	virtual ~Observer();	virtual void Update(Subject* sub) = 0;	virtual void PrintInfo() = 0;protected:	Observer();	State _st;private:};class ConcreteObserverA:public Observer{public:	virtual Subject* GetSubject();	ConcreteObserverA(Subject* sub);	virtual ~ConcreteObserverA();	//传入Subject作为参数，这样可以让一个View属于多个的Subject。	void Update(Subject* sub);	void PrintInfo();protected:private:	Subject* _sub;};class ConcreteObserverB:public Observer{public:	virtual Subject* GetSubject();	ConcreteObserverB(Subject* sub);	virtual ~ConcreteObserverB();	//传入Subject作为参数，这样可以让一个View属于多个的Subject。	void Update(Subject* sub);	void PrintInfo();protected:private:	Subject* _sub;};#endif //~_OBSERVER_H_

Observer.cpp

//Observer.cpp#include "Observer.h"#include "Subject.h"#include 
   
    #include 
    
     using namespace std;Observer::Observer(){	_st = '\0';}Observer::~Observer(){}ConcreteObserverA::ConcreteObserverA(Subject* sub){	_sub = sub;	_sub->Attach(this);}ConcreteObserverA::~ConcreteObserverA(){	_sub->Detach(this);	if (_sub != 0)		delete _sub;}Subject* ConcreteObserverA::GetSubject(){	return _sub;}void ConcreteObserverA::PrintInfo(){	cout<<"ConcreteObserverA observer.... "<<_sub->GetState()<
     
      GetState();	PrintInfo();}ConcreteObserverB::ConcreteObserverB(Subject* sub){	_sub = sub;	_sub->Attach(this);}ConcreteObserverB::~ConcreteObserverB(){	_sub->Detach(this);	if (_sub != 0)	{		delete _sub;	}}Subject* ConcreteObserverB::GetSubject(){	return _sub;}void ConcreteObserverB::PrintInfo(){	cout<<"ConcreteObserverB observer.... "<<_sub->GetState()<
      
       GetState();	PrintInfo();}

main.cpp

#include "Subject.h"#include "Observer.h"#include 
   
    using namespace std;int main(){	ConcreteSubject* sub = new ConcreteSubject();	Observer* o1 = new ConcreteObserverA(sub);	Observer* o2 = new ConcreteObserverB(sub);	sub->SetState("old");	sub->Notify();	sub->SetState("new"); //也可以由Observer调用	sub->Notify();    return 0;}