观察者设计模式是否已在STL中定义(如
Java中的java.util.Observer和java.util.Observable)？
解决方法
这是一个参考实现(从
Wikipedia开始).
#include <iostream>
#include <string>
#include <map>
#include <boost/foreach.hpp>
class SupervisedString;
class IObserver{
public:
virtual void handleEvent(const SupervisedString&) = 0;
};
class SupervisedString{ // Observable class
std::string _str;
std::map<IObserver* const,IObserver* const> _observers;
typedef std::map<IObserver* const,IObserver* const>::value_type item;
void _Notify(){
BOOST_FOREACH(item iter,_observers){
iter.second->handleEvent(*this);
}
}
public:
void add(IObserver& ref){
_observers.insert(item(&ref,&ref));
}
void remove(IObserver& ref){
_observers.erase(&ref);
}
const std::string& get() const{
return _str;
}
void reset(std::string str){
_str = str;
_Notify();
}
};
class Reflector: public IObserver{ // Prints the observed string into std::cout
public:
virtual void handleEvent(const SupervisedString& ref){
std::cout<<ref.get()<<std::endl;
}
};
class Counter: public IObserver{ // Prints the length of observed string into std::cout
virtual void handleEvent(const SupervisedString& ref){
std::cout<<"length = "<<ref.get().length()<<std::endl;
}
};
int main(){
SupervisedString str;
Reflector refl;
Counter cnt;
str.add(refl);
str.reset("Hello,World!");
std::cout<<std::endl;
str.remove(refl);
str.add (cnt);
str.reset("World,Hello!");
std::cout<<std::endl;
return 0;
}
