C++ 使用'std::function'从另一个对象调用对象的成员`
我试图在对象之间创建一个通信系统,其中控制器对象保留其他对象的成员函数向量,并在需要时调用它们。C++ 使用'std::function'从另一个对象调用对象的成员`,c++,oop,c++11,callback,std-function,C++,Oop,C++11,Callback,Std Function,我试图在对象之间创建一个通信系统,其中控制器对象保留其他对象的成员函数向量,并在需要时调用它们。 我读了几篇关于std::function用法的文章,但找不到一篇介绍这个用例的文章 我的代码是: #include <functional> #include <Windows.h> class Callable { }; class ClassA : public Callable { public: double CallThis(doubl
我读了几篇关于
std::function
用法的文章,但找不到一篇介绍这个用例的文章
我的代码是:
#include <functional>
#include <Windows.h>
class Callable
{
};
class ClassA : public Callable
{
public:
double CallThis(double x, int y) const
{
MessageBoxW(NULL, L"CallThis() is called.", L"In ClassA", MB_ICONINFORMATION);
return x + y;
}
};
class ClassB : public Callable
{
public:
double CallMe(double x, int y) const
{
MessageBoxW(NULL, L"CallMe() is called.", L"In ClassB", MB_ICONINFORMATION);
return x + y;
}
};
class Caller
{
public:
void AddSubscriber( const Callable & ObjectToCall,
const std::function<double(const Callable &, double, int)> & Subscriber)
{
Subscribers.push_back(Subscriber);
ObjectsToBeCalled.push_back(ObjectToCall);
}
void CallSubscribers()
{
for (size_t i=0; i<Subscribers.size(); i++)
{
Subscribers[i](ObjectsToBeCalled[i], 1.0, 2);
}
}
private:
std::vector<std::function<double(const Callable &, double, int)>> Subscribers;
std::vector<const Callable &> ObjectsToBeCalled;
};
int APIENTRY wWinMain( _In_ HINSTANCE hInstance,
_In_opt_ HINSTANCE hPrevInstance,
_In_ LPTSTR lpCmdLine,
_In_ int nCmdShow)
{
// ...
ClassA ObjectA;
ClassB ObjectB;
Caller ObjectCaller;
ObjectCaller.AddSubscriber(ObjectA, &ClassA::CallThis);
ObjectCaller.AddSubscriber(ObjectA, &ClassB::CallMe);
Sleep(5000);
ObjectCaller.CallSubscribers();
// ...
}
我做错了什么?如何运行此代码
(我的IDE是Microsoft Visual Studio 2012。)查看您的代码,您最好先存储
std::function
,然后使用std::bind
将对象绑定到成员函数
template <typename F>
void AddSubscriber( const Callable & obj,
F subscriber)
{
Subscribers.push_back(std::bind(subscriber, obj, _1, _2));
}
然后从调用方进行绑定
Caller c;
ClassA a;
using namespace std::placeholders;
c.AddSubscriber(std::bind(&ClassA::CallThis, a, _1, _2));
在阅读完juanchopanza的答案后,我重写了我的代码,如附件所示。现在,它的工作如预期
class ClassA
{
public:
double CallThis(double x, int y) const
{
MessageBoxW(NULL, L"CallThis() is called.", L"In ClassA", MB_ICONINFORMATION);
return x + y;
}
};
class ClassB
{
public:
double CallMe(double x, int y) const
{
MessageBoxW(NULL, L"CallMe() is called.", L"In ClassB", MB_ICONINFORMATION);
return x + y;
}
};
class Caller
{
public:
void AddSubscriber(std::function<double(double, int)> Subscriber)
{
Subscribers.push_back(Subscriber);
}
void CallSubscribers()
{
for (const auto & Subscriber : Subscribers)
{
Subscriber(1.0, 2);
}
}
private:
std::vector<std::function<double(double, int)>> Subscribers;
};
int APIENTRY wWinMain( _In_ HINSTANCE hInstance,
_In_opt_ HINSTANCE hPrevInstance,
_In_ LPTSTR lpCmdLine,
_In_ int nCmdShow)
{
// ...
ClassA ObjectA;
ClassB ObjectB;
Caller ObjectCaller;
ObjectCaller.AddSubscriber(std::bind(&ClassA::CallThis, ObjectA, std::placeholders::_1, std::placeholders::_2));
ObjectCaller.AddSubscriber(std::bind(&ClassB::CallMe, ObjectB, std::placeholders::_1, std::placeholders::_2));
Sleep(5000);
ObjectCaller.CallSubscribers();
// ...
}
A类
{
公众:
double CallThis(double x,int y)const
{
MessageBoxW(NULL,L“CallThis()被调用”,L“在ClassA中”,MB_ICONINFORMATION);
返回x+y;
}
};
B类
{
公众:
双CallMe(双x,整数y)常数
{
MessageBoxW(NULL,调用L“CallMe()”,L“在类B中”,MB_ICONINFORMATION);
返回x+y;
}
};
类调用者
{
公众:
void AddSubscriber(std::函数Subscriber)
{
订阅者。推回(订阅者);
}
void CallSubscribers()
{
用于(常数自动和订户:订户)
{
认购人(1.0,2);
}
}
私人:
std::向量订户;
};
国际货币基金组织,
_在当前情况下,
_在LPTSTR lpCmdLine中,
_In_uuint(nCmdShow)
{
// ...
A类对象A;
B类对象B;
调用者对象调用者;
AddSubscriber(std::bind(&ClassA::CallThis,ObjectA,std::placeholders::_1,std::placeholders::_2));
AddSubscriber(std::bind(&ClassB::CallMe,ObjectB,std::placeholders::_1,std::placeholders::_2));
睡眠(5000);
ObjectCaller.CallSubscribers();
// ...
}
std::vector对象被调用代码>您正在尝试声明引用向量。这是非法的,因为vector存储元素的副本,而引用是不可复制的。尝试将其声明为std::vector
,并查看它是否编译。std::function
的行为就像是在向其传递指向成员的指针时自动调用std::mem\u fn
。@Xeo Right,谢谢。我删除了开头的句子。保留一个回调容器似乎更容易管理。FWIW,我建议在这里调用emplace\u back
。
Caller c;
ClassA a;
using namespace std::placeholders;
c.AddSubscriber(std::bind(&ClassA::CallThis, a, _1, _2));
class ClassA
{
public:
double CallThis(double x, int y) const
{
MessageBoxW(NULL, L"CallThis() is called.", L"In ClassA", MB_ICONINFORMATION);
return x + y;
}
};
class ClassB
{
public:
double CallMe(double x, int y) const
{
MessageBoxW(NULL, L"CallMe() is called.", L"In ClassB", MB_ICONINFORMATION);
return x + y;
}
};
class Caller
{
public:
void AddSubscriber(std::function<double(double, int)> Subscriber)
{
Subscribers.push_back(Subscriber);
}
void CallSubscribers()
{
for (const auto & Subscriber : Subscribers)
{
Subscriber(1.0, 2);
}
}
private:
std::vector<std::function<double(double, int)>> Subscribers;
};
int APIENTRY wWinMain( _In_ HINSTANCE hInstance,
_In_opt_ HINSTANCE hPrevInstance,
_In_ LPTSTR lpCmdLine,
_In_ int nCmdShow)
{
// ...
ClassA ObjectA;
ClassB ObjectB;
Caller ObjectCaller;
ObjectCaller.AddSubscriber(std::bind(&ClassA::CallThis, ObjectA, std::placeholders::_1, std::placeholders::_2));
ObjectCaller.AddSubscriber(std::bind(&ClassB::CallMe, ObjectB, std::placeholders::_1, std::placeholders::_2));
Sleep(5000);
ObjectCaller.CallSubscribers();
// ...
}