好吧,你让我工作。困难的部分是尝试匹配 C# 事件的确切使用模式。如果你跳过它,有更简单的方法来做你所要求的。(我的同事 Jason 在所有地方都使用了一个 Notifier 对象。)不管怎样,这里有一些令人难以置信的无聊代码,它可以满足您的需求。不幸的是,它不允许您将参数从 Subject 传递给 Observer。为此,您需要添加更多智能。
#include "stdafx.h"
#include <iostream>
#include <string>
#include <list>
#include <algorithm>
#include <boost/tr1/functional.hpp>
#include <boost/tr1/memory.hpp>
using namespace std;
using namespace std::tr1;
template <typename T>
class ObserverHandle
{
public:
typedef boost::function<void (T*)> const UnderlyingFunction;
ObserverHandle(UnderlyingFunction underlying)
: _underlying(new UnderlyingFunction(underlying))
{
}
void operator()(T* data) const
{
(*_underlying)(data);
}
bool operator==(ObserverHandle<T> const& other) const
{
return (other._underlying == _underlying);
}
private:
shared_ptr<UnderlyingFunction> const _underlying;
};
class BaseDelegate
{
public:
virtual bool operator==(BaseDelegate const& other)
{
return false;
}
virtual void operator() () const = 0;
};
template <typename T>
class Delegate : public BaseDelegate
{
public:
Delegate(T* observer, ObserverHandle<T> handle)
: _observer(observer),
_handle(handle)
{
}
virtual bool operator==(BaseDelegate const& other)
{
BaseDelegate const * otherPtr = &other;
Delegate<T> const * otherDT = dynamic_cast<Delegate<T> const *>(otherPtr);
return ((otherDT) &&
(otherDT->_observer == _observer) &&
(otherDT->_handle == _handle));
}
virtual void operator() () const
{
_handle(_observer);
}
private:
T* _observer;
ObserverHandle<T> _handle;
};
class Event
{
public:
template <typename T>
void add(T* observer, ObserverHandle<T> handle)
{
_observers.push_back(shared_ptr<BaseDelegate>(new Delegate<T>(observer, handle)));
}
template <typename T>
void remove(T* observer, ObserverHandle<T> handle)
{
// I should be able to come up with a bind2nd(equals(dereference(_1))) kind of thing, but I can't figure it out now
Observers::iterator it = find_if(_observers.begin(), _observers.end(), Compare(Delegate<T>(observer, handle)));
if (it != _observers.end())
{
_observers.erase(it);
}
}
void operator()() const
{
for (Observers::const_iterator it = _observers.begin();
it != _observers.end();
++it)
{
(*(*it))();
}
}
private:
typedef list<shared_ptr<BaseDelegate>> Observers;
Observers _observers;
class Compare
{
public:
Compare(BaseDelegate const& other)
: _other(other)
{
}
bool operator() (shared_ptr<BaseDelegate> const& other) const
{
return (*other) == _other;
}
private:
BaseDelegate const& _other;
};
};
// Example usage:
class SubjectA
{
public:
Event event;
void do_event()
{
cout << "doing event" << endl;
event();
cout << "done" << endl;
}
};
class ObserverA
{
public:
void test(SubjectA& subject)
{
subject.do_event();
cout << endl;
subject.event.add(this, _observe);
subject.do_event();
subject.event.remove(this, _observe);
cout << endl;
subject.do_event();
cout << endl;
subject.event.add(this, _observe);
subject.event.add(this, _observe);
subject.do_event();
subject.event.remove(this, _observe);
subject.do_event();
subject.event.remove(this, _observe);
cout << endl;
}
void observe()
{
cout << "..observed!" << endl;
}
private:
static ObserverHandle<ObserverA> _observe;
};
// Here's the trick: make a static object for each method you might want to turn into a Delegate
ObserverHandle<ObserverA> ObserverA::_observe(boost::bind(&ObserverA::observe, _1));
int _tmain(int argc, _TCHAR* argv[])
{
SubjectA sa;
ObserverA oa;
oa.test(sa);
return 0;
}
这是输出:
做完 事件
做事件
..观察到!
完毕
做完 事件
做事件
..观察到!
..观察到的!
做完
事件
..观察到!
完毕