考虑一下代码段:
# include <iostream>
# include <boost/scoped_ptr.hpp>
# include <boost/shared_ptr.hpp>
# include <boost/function.hpp>
# include <boost/array.hpp>
# include <boost/asio.hpp>
# include <boost/thread.hpp>
# include <boost/thread/locks.hpp>
# include <boost/bind.hpp>
# include <boost/noncopyable.hpp>
# include <boost/variant.hpp>
class DataLink {};
class Metadata {};
class Image {};
typedef boost::function<void( DataLink const&, Metadata const& , Image const& )> Handler ;
typedef boost::function<void( Metadata const& , Image const& )> Handler2 ;
typedef boost::function<void( Image const& )> Handler3 ;
typedef boost::variant<DataLink, Metadata, Image> Variant;
enum callbackHandler { link_enum, meta_enum, image_enum };
class Worker {
Handler callBack ;
//Handler2 callBack2 ;
//Handler3 callBack3 ;
DataLink dlink;
Metadata meta ;
Image img ;
callbackHandler handlerEnum ;
public :
Worker ( const Handler& handler )
: callBack ( handler )
{}
//Worker ( const Handler2& handler )
//: callBack2 ( handler )
// {}
//Worker ( const Handler3& handler )
//: callBack3 ( handler )
// {}
void Image ( ) {
// update the img object
// invoke call back
handlerEnum = image_enum ;
//const std::type_info& xxx = callBack.target_type();
//std::cout << xxx.raw_name() << std::endl;
callBack ( dlink, meta, img ) ;
}
void Metadata ( ) {
// update the meta object
// invoke call back
handlerEnum = meta_enum ;
callBack ( dlink, meta, img ) ;
}
void Dlink ( ) {
// update the link object
// invoke call back
handlerEnum = link_enum ;
callBack ( dlink, meta, img ) ;
}
callbackHandler getHandlerType() { return handlerEnum ; }
};
class Foo {
Worker *ptrWorker ;
public :
Foo ()
: ptrWorker( 0 )
{}
void callback ( DataLink const& d, Metadata const& m , Image const& i ) {
callbackHandler tt = ptrWorker->getHandlerType();
if ( tt == image_enum ) {
std::cout << "Image object " << std::endl;
}
if ( tt == meta_enum ) {
std::cout << "Meta object " << std::endl;
}
if ( tt == link_enum ) {
std::cout << "Link object " << std::endl;
}
}
bool start () {
ptrWorker = new ( std::nothrow ) Worker ( boost::bind ( &Foo::callback, this, _1, _2, _3 ) );
if ( !ptrWorker ) {
return - 1 ;
}
}
void testWorker() {
ptrWorker->Image() ;
ptrWorker->Metadata() ;
ptrWorker->Dlink() ;
}
};
int main() {
Foo f;
f.start() ;
f.testWorker() ;
std::cin.get() ;
}
注释掉的构造函数允许我添加对Handler2和Handler3的支持,但有没有办法确定传递给Worker类的构造函数的处理程序?目前,成员函数Metadata,Image和Dlink使用'callBack'对象。如果用户处理程序在另一个处理程序中传递,我需要区分 - 比如Handler2
我需要使用枚举来实现,有效的是我自己的类型系统(在描述性联盟的行中 - 也就是变体),这也是设计需要一点点的确定标志在这种情况下我会这么想,我愿意重新设计。必须拥有N-1个虚拟处理程序(即,在任何时候只使用一个处理程序而其他人只是在那里做任何事情)在类中定义了混淆和低凝聚力的对象模型,但谁知道。
答案 0 :(得分:0)
您可以使用从虚拟基类派生的仿函数来实现它:
struct CallbackBase
{
// Dummy virtual functions that does nothing
virtual operator()(DataLink const &, Metadata const &, Image const &) {}
virtual operator()(Metadata const &, Image const &) {}
virtual operator()(Image const &) {}
};
class Worker
{
CallbackBase &callback_;
public:
Worker(const CallbackBase &callback)
: callback_(callback)
{ }
void Image()
{
// Do something...
callback_(img);
}
void Metadata()
{
// Do something...
callback_(meta, img);
}
void Dlink()
{
// Do something...
callback_(dlink, meta, img);
}
};
struct MyCallback : public CallbackBase
{
virtual operator()(Image const &)
{
// Do something useful here
}
};
MyCallback my_callback;
Worker my_worker(my_callback);
由于基本回调类中的重载,Worker
类可以在正确的位置调用它们中的任何一个,而您只实现派生回调类中实际需要的回调。