设计模式--Observer(转自k_eckel)

最新推荐文章于 2019-07-09 13:33:44 发布

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最新推荐文章于 2019-07-09 13:33:44 发布

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本文介绍了一种使用C++实现的观察者模式，包括Subject和Observer类的定义与交互过程。展示了如何通过Attach、Detach和Notify方法来管理观察者，并演示了具体的应用案例。

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Subject.h

#ifndef _ADAPTER_H
#define _ADAPTER_H
#include<iostream>
#include<list>
#include<string>
class Observer;
class Subject
{
public:
virtual ~Subject();
virtual void Attach(Observer* obv);
virtual void Detach(Observer* obv);
virtual void Notify();
virtual void SetState(const std::string& st) = 0;
virtual std::string GetState() = 0;
protected:
Subject();
private:
std::list<Observer*>* _obvs;
};
class ConcreteSubject :
public Subject
{
public:
ConcreteSubject();
~ConcreteSubject();
std::string GetState();
void SetState(const std::string& st);
private:
std::string _st;
};
#endif

Subject.cpp

#include"stdafx.h"
#include"Subject.h"
#include<iostream>
#include"Observer.h"

Subject::Subject()
{
_obvs = new std::list <Observer* > ;
}
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()
{
std::list<Observer*>::iterator it;
it = _obvs->begin();
for (; it != _obvs->end(); it++)
{
(*it)->Update(this);
}
}
ConcreteSubject::ConcreteSubject()
{
_st = '\0';
}
ConcreteSubject::~ConcreteSubject()
{}
std::string ConcreteSubject::GetState()
{
return _st;
}
void ConcreteSubject::SetState(const std::string& st)
{
_st = st;
}

Observer.h

#include"Subject.h"
#include<string>
#include<iostream>
class Observer
{
public:
virtual ~Observer();
virtual void Update(Subject* sub) = 0;
virtual void PrintInfo() = 0;
protected:
Observer();
std::string _st;
};
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();
private:
Subject* _sub;
};
class ConcreteObserverB :
public Observer
{
public:
virtual Subject* GetSubject();
ConcreteObserverB(Subject* sub);
virtual ~ConcreteObserverB();
void Update(Subject* sub);
void PrintInfo();
private:
Subject* _sub;
};

Observer.cpp

#include"stdafx.h"
#include"Observer.h"
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()
{
std::cout << "ConcreteObserverA observer...." << _sub->GetState() << std::endl;
}
void ConcreteObserverA::Update(Subject* sub)
{
_st = sub->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()
{
std::cout << "ConcreteObserverB observer...." << _sub->GetState() << std::endl;
}
void ConcreteObserverB::Update(Subject* sub)
{
_st = sub->GetState();
PrintInfo();
}

main.cpp

int _tmain(int argc, _TCHAR* argv[])
{
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;
}