转自：http://blog.csdn.net/yhjvc/archive/2005/11/25/536589.aspx
用C++ template实现的通用Observer代码。本文并无神秘之处，template只是运用在对状态信息类型的泛化。过多的细节就没必要不讲了，我想各位看官比我更明白吧
/*
Design Pattern implementation with C++ template - Observer
*/
#ifndef _OBSERVER_H_
#define _OBSERVER_H_
#include<vector>
template<typename Msg>
struct helper;
template<typename Msg>
struct subject;
template<typename Msg>
class observer
{
friend class helper<Msg>;
protected:
observer():psbj_(NULL)
{}
public:
virtual ~observer()
{
if(psbj_)
psbj_->detach(*this);
}
virtual void update(const Msg&)=0;
private:
subject<Msg>* psbj_;
};
template<typename Msg>
class subject
{
friend class helper<Msg>;
public:
virtual ~subject()
{
typename std::vector<observer<Msg>*>::iterator begin = obsvrvec_.begin();
typename std::vector<observer<Msg>*>::iterator end = obsvrvec_.end();
for(; begin!=end; ++begin)
helper<Msg>::attachtosubject(NULL, *begin);
}
void attach(observer<Msg>& rhs) //register
{
obsvrvec_.push_back(&rhs);
helper<Msg>::attachtosubject(this, &rhs);
}
void detach(observer<Msg>& rhs) //unregister
{
typename std::vector<observer<Msg>*>::iterator matched = find(obsvrvec_.begin(), obsvrvec_.end(), &rhs);
if(matched != obsvrvec_.end())
obsvrvec_.erase(matched);
}
void notify() //notify all observers
{
typename std::vector<observer<Msg>*>::iterator begin = obsvrvec_.begin();
typename std::vector<observer<Msg>*>::iterator end = obsvrvec_.end();
for(; begin!=end; ++begin)
(*begin)->update(message_);
}
protected:
Msg& message()
{ return message_; }
const Msg& message() const
{ return message_; }
void message(const Msg& rhs)
{ message_ = rhs; }
private:
Msg message_;
std::vector<observer<Msg>*> obsvrvec_;
};
template<typename Msg>
struct helper
{
static void attachtosubject(subject<Msg>* sbj, observer<Msg>* obsv)
{ obsv->psbj_ = sbj; }
};
#endif //_OBSERVER_H_
下面是应用的示例代码
class ConcreteObserver1:public observer<string>
{
public:
void update(const string& message)
{ cout<<message<<endl; }
};
class ConcreteObserver2:public observer<string>
{
public:
void update(const string& message)
{
copy(message.rbegin(), message.rend(), ostream_iterator<string::value_type>(cout));
cout<<endl;
}
};
class ConcreteSubject:public subject<string>
{
public:
void set(const string& str)
{ message(str); }
};
int main()
{
ConcreteSubject subject;
ConcreteObserver1 o1;
ConcreteObserver2 o2;
subject.attach(o1);
subject.attach(o2);
subject.set("show me the money");
subject.notify();
}
