因为我喜欢用C#和C++编程,所以我正在实现一个C#类事件系统作为我的计划C++ SFML的坚实基础-GUI。std :: tr1 :: function :: target <TFuncPtr> and co-/ contravariance
这只是我的代码的摘录,我希望这个澄清我的概念:
// Event.h
// STL headers:
#include <functional>
#include <type_traits>
#include <iostream>
// boost headers:
#include <boost/signals/trackable.hpp>
#include <boost/signal.hpp>
namespace Utils
{
namespace Gui
{
#define IMPLEMENTS_EVENT(EVENTNAME, EVENTARGS) public: \
Utils::Gui::IEvent<EVENTARGS>& EVENTNAME() { return m_on##EVENTNAME; } \
protected: \
virtual void On##EVENTNAME(EVENTARGS& e) { m_on##EVENTNAME(this, e); } \
private: \
Utils::Gui::Event<EVENTARGS> m_on##EVENTNAME;
#define MAKE_EVENTFIRING_CLASS(EVENTNAME, EVENTARGS) class Fires##EVENTNAME##Event \
{ \
IMPLEMENTS_EVENT(EVENTNAME, EVENTARGS); \
};
class EventArgs
{
public:
static EventArgs Empty;
};
EventArgs EventArgs::Empty = EventArgs();
template<class TEventArgs>
class EventHandler : public std::function<void (void*, TEventArgs&)>
{
static_assert(std::is_base_of<EventArgs, TEventArgs>::value,
"EventHandler must be instantiated with a TEventArgs template paramater type deriving from EventArgs.");
public:
typedef void Signature(void*, TEventArgs&);
typedef void (*HandlerPtr)(void*, TEventArgs&);
EventHandler() : std::function<Signature>() { }
template<class TContravariantEventArgs>
EventHandler(const EventHandler<TContravariantEventArgs>& rhs)
: std::function<Signature>(reinterpret_cast<HandlerPtr>(*rhs.target<EventHandler<TContravariantEventArgs>::HandlerPtr>()))
{
static_assert(std::is_base_of<TContravariantEventArgs, TEventArgs>::value,
"The eventHandler instance to copy does not suffice the rules of contravariance.");
}
template<class F>
EventHandler(F f) : std::function<Signature>(f) { }
template<class F, class Allocator>
EventHandler(F f, Allocator alloc) : std::function<Signature>(f, alloc) { }
};
template<class TEventArgs>
class IEvent
{
public:
typedef boost::signal<void (void*, TEventArgs&)> SignalType;
void operator+= (const EventHandler<TEventArgs>& eventHandler)
{
Subscribe(eventHandler);
}
void operator-= (const EventHandler<TEventArgs>& eventHandler)
{
Unsubscribe(eventHandler);
}
virtual void Subscribe(const EventHandler<TEventArgs>& eventHandler) = 0;
virtual void Subscribe(const EventHandler<TEventArgs>& eventHandler, int group) = 0;
virtual void Unsubscribe(const EventHandler<TEventArgs>& eventHandler) = 0;
};
template<class TEventArgs>
class Event : public IEvent<TEventArgs>
{
public:
virtual void Subscribe(const EventHandler<TEventArgs>& eventHandler)
{
m_signal.connect(*eventHandler.target<EventHandler<TEventArgs>::HandlerPtr>());
}
virtual void Subscribe(const EventHandler<TEventArgs>& eventHandler, int group)
{
m_signal.connect(group, *eventHandler.target<EventHandler<TEventArgs>::HandlerPtr>());
}
virtual void Unsubscribe(const EventHandler<TEventArgs>& eventHandler)
{
m_signal.disconnect(*eventHandler.target<EventHandler<TEventArgs>::HandlerPtr>());
}
void operator() (void* sender, TEventArgs& e)
{
m_signal(sender, e);
}
private:
SignalType m_signal;
};
class IEventListener : public boost::signals::trackable
{
};
};
};
正如你所看到的,我使用boost ::信号作为我的实际事件系统,但我将其封装与IEvent接口(实际上是一个抽象类),以防止事件侦听器通过operator()触发事件。
为了方便起见,我重载了加法赋值和减法赋值运算符。如果我现在从IEventListener派生出我的事件监听类,那么我可以编写代码而不必担心信号中的悬挂函数指针。
到目前为止,我测试我的结果,但我有麻烦std::tr1::function::target<TFuncPtr>()
:
class BaseEventArgs : public Utils::Gui::EventArgs
{
};
class DerivedEventArgs : public BaseEventArgs
{
};
void Event_BaseEventRaised(void* sender, BaseEventArgs& e)
{
std::cout << "Event_BaseEventRaised called";
}
void Event_DerivedEventRaised(void* sender, DerivedEventArgs& e)
{
std::cout << "Event_DerivedEventRaised called";
}
int main()
{
using namespace Utils::Gui;
typedef EventHandler<BaseEventArgs>::HandlerPtr pfnBaseEventHandler;
typedef EventHandler<DerivedEventArgs>::HandlerPtr pfnNewEventHandler;
// BaseEventHandler with a function taking a BaseEventArgs
EventHandler<BaseEventArgs> baseEventHandler(Event_BaseEventRaised);
// DerivedEventHandler with a function taking a DerivedEventArgs
EventHandler<DerivedEventArgs> newEventHandler(Event_DerivedEventRaised);
// DerivedEventHandler with a function taking a BaseEventArgs -> Covariance
EventHandler<DerivedEventArgs> covariantBaseEventHandler(Event_BaseEventRaised);
const pfnBaseEventHandler* pBaseFunc = baseEventHandler.target<pfnBaseEventHandler>();
std::cout << "baseEventHandler function pointer is " << ((pBaseFunc != nullptr) ? "valid" : "invalid") << std::endl;
const pfnNewEventHandler* pNewFunc = newEventHandler.target<pfnNewEventHandler>();
std::cout << "baseEventHandler function pointer is " << ((pNewFunc != nullptr) ? "valid" : "invalid") << std::endl;
// Here is the error, covariantBaseEventHandler actually stores a pfnBaseEventHandler:
pNewFunc = covariantBaseEventHandler.target<pfnNewEventHandler>();
std::cout << "covariantBaseEventHandler as pfnNewEventHandler function pointer is " << ((pNewFunc != nullptr) ? "valid" : "invalid") << std::endl;
// This works as expected, but template forces compile-time knowledge of the function pointer type
pBaseFunc = covariantBaseEventHandler.target<pfnBaseEventHandler>();
std::cout << "covariantBaseEventHandler as pfnBaseEventHandler function pointer is " << ((pBaseFunc != nullptr) ? "valid" : "invalid") << std::endl;
return EXIT_SUCCESS;
}
的EventHandler<TEventArgs>::target<TFuncPtr>()
方法只会返回一个有效的指针,如果TFuncPtr是存储在仿函数类型完全相同的,无论协方差。 由于RTTI检查,它禁止访问指针作为一个标准的弱类型C函数指针,这是一种恼人的情况下,像这样的一种。
EventHandler属于DerivedEventArgs类型,但仍指向pfnBaseEventHandler函数,即使该函数是通过构造函数运行的。
这意味着,std :: tr1 ::函数本身“支持”反转,但我找不到一种简单的从std :: tr1 :: funcion对象中获取函数指针的方法, t在编译时知道它的类型,这是模板参数所需的。
我希望在像这样的情况下,他们添加了一个像RAII指针类型一样的简单get()方法。我想知道是否有办法解决这个问题,最好是在编译时通过模板(我认为这是唯一的方法)。
要格式化代码,请选择并点击文本输入区域上方的1010按钮 - 不要使用HTML预编码和/或代码标签。 – 2010-07-12 11:17:37
@ Sebastion:使用编辑窗口顶部的小101010按钮格式化代码。 (并且您阅读了编辑窗口右侧的帮助以获得帮助。)我进入并格式化了您的代码。 – sbi 2010-07-12 11:17:39
是的,我阅读了这个缩进的东西并进行了测试,但由于预览没有立即格式化代码,我使用HTML标签。现在我肯定更聪明。感谢你们三个整理我的东西。 @Roger Pate:是的,这就是我所怀疑的......我现在要去尝试设置一个简短的例子。 – 2010-07-12 11:55:00