FLTK 回调不会接受我的函数指针 [英] FLTK callbacks won't accept my function pointers

问题描述

所以我有这门课它应该包含我的窗口和我将用作回调的所有函数.

So I have this class which is supposed to contain my window and all the functions that I'm going to use as callbacks.

#include <FL/Fl.H>
#include <FL/Fl_Double_Window.H>
#include <FL/Fl_Box.H>
#include <FL/Fl_Group.H>
#include <FL/Fl_Value_Input.H>
#include <FL/Fl_Button.H>
#include <FL/Fl_Slider.H>
#include <FL/Fl_Check_Button.H>
#include "world.hpp"

class Controller
{
    private:
        Fl_Double_Window *window;
    public:
        int process(int argc, char **argv);
        void nextStep(Fl_Widget *widget, void *data);
        void togglePlay(Fl_Widget *widget, void *data);
        void newWorld(Fl_Widget *widget, void *data);
        void randFill(Fl_Widget *widget, void *data);
        void togglePreviz(Fl_Widget *widget, void *data);
        void updateSpeed(Fl_Widget *widget, void *data);
        Fl_Double_Window* make_window();
};

现在在make_window()"(最初使用 FLUID 创建)的实现中，我想将我的功能分配给适当的小部件.

Now in the implementation of "make_window()" (which was originally created using FLUID) I want to assign my functions to the appropriate widgets.

Fl_Double_Window* Controller::make_window() 
{
    //Generated with FLUID designer
    Fl_Double_Window* w;
    { Fl_Double_Window* o = new Fl_Double_Window(1200, 900);
    w = o; if (w) {/* empty */}
    o->color(FL_FOREGROUND_COLOR);
    { World* o = new World(25, 25, 800, 800);
      o->box(FL_DOWN_BOX);
      o->color((Fl_Color)30);
      o->end();
    } // Fl_Group* o
    { Fl_Group* o = new Fl_Group(850, 25, 300, 805);
      o->box(FL_DOWN_BOX);
      o->color(FL_INACTIVE_COLOR);
      { Fl_Value_Input* o = new Fl_Value_Input(875, 50, 100, 24, "Cellules");
        o->align(Fl_Align(FL_ALIGN_RIGHT));
      } // Fl_Value_Input* o
      { Fl_Button* o = new Fl_Button(900, 100, 200, 40, "Creation Monde");
        o->box(FL_ROUNDED_BOX);
        o->callback(newWorld);
      } // Fl_Button* o
      { Fl_Slider* o = new Fl_Slider(FL_HOR_NICE_SLIDER, 900, 175, 200, 25, "Vitesse");
        o->callback(updateSpeed);
        o->align(Fl_Align(FL_ALIGN_TOP));
        o->bounds(0.0, 1.0);
      } // Fl_Slider* o
      { Fl_Check_Button* o = new Fl_Check_Button(875, 225, 64, 20, "Mode PreViz");
        o->callback(togglePreviz);
        o->down_box(FL_DOWN_BOX);
      } // Fl_Check_Button* o
      { Fl_Value_Input* o = new Fl_Value_Input(875, 300, 100, 24, "Taux");
        o->align(Fl_Align(FL_ALIGN_RIGHT));
      } // Fl_Value_Input* o
      { Fl_Button* o = new Fl_Button(900, 350, 200, 40, "Remplissage Aleatoire");
        o->callback(randFill);
        o->box(FL_ROUNDED_BOX);
      } // Fl_Button* o
      { Fl_Button* o = new Fl_Button(950, 500, 100, 100, "@>");
        o->callback(togglePlay);
        o->box(FL_ROUNDED_BOX);
        o->labelsize(50);
      } // Fl_Button* o
      { Fl_Button* o = new Fl_Button(950, 650, 100, 100, "@->");
        o->callback(nextStep);
        o->box(FL_ROUNDED_BOX);
        o->labelsize(50);
      } // Fl_Button* o
      o->end();
    } // Fl_Group* o
    o->end();
  } // Fl_Double_Window* o
  return w;
}

问题是在我调用o->callback(myFunctionPointer);"的每一行我收到一个错误，告诉我

The problem is that at every line where I call "o->callback(myFunctionPointer);" I get an error telling me that

no instance of overloaded function "Fl_Button::callback" matches the argument list -- argument types are: (void (Fl_Widget *widget, void *data)) -- object type is: Fl_Button

根据我的研究，这应该意味着我没有在回调"函数中发送适当数量或类型的参数.在深入研究文档后，我发现回调"函数至少需要一个指向 Fl_callback 对象的指针，但我已经看到人们只是发送一个函数指针的代码示例，它似乎在他们的代码上工作得很好.

From what I've researched it should mean that I don't send the appropriate number or type of parameters in my "callback" function. After digging in the documentation, I've found that the "callback" function expects at least a pointer to a Fl_callback object but I've seen examples of code where people just send a function pointer and it seems to work just fine on their code.

为什么 FLTK 不接受我的指示?我宣布他们错了吗?

Why won't FLTK accept my pointers ? Have I declared them wrong ?

任何帮助将不胜感激

谢谢

推荐答案

FLTK 回调是自由函数(静态或非成员函数).您正在传递实例成员函数.如果不需要 this 参数，您可以声明您的函数 static.或者安装一些特别的回调管理器(假设支持 c++17):

FLTK callbacks are free functions( static or none-member fuunctions ). You are passing instance member functions. If the this parameter is not needed you can declare your functions static. Or install some ad-hoc callback manager(assuming c++17 support):

typedef void fltk_cb(Fl_Widget *, void*);

void Controller::nextStep(Fl_Widget *);

template<auto cb, typename cb_type=decltype(cb)>
struct mem_cb{
static_assert(std::is_same_v<cb_type, void Controller::(*)(Fl_Widget *)>,"incompatible type");
    constexpr operator fltk_cb*()const{return &static_cb;};
    static void static_cb(Fl_Widget * w, void * that){
        (reinterpret_cast<Controller*>(that)->*cb)(w);
    };
};

//...
 o->callback(mem_cb<&nextStep>{},this);

c++17 之前的语法可能很笨拙.使用 std::function 或 boost::signal2 和稍微复杂一点的更好的临时回调管理可以实现.但我想你只需要一些开胃菜.更短的解决方案是不捕获 lambda:

prior to c++17 syntax can be awkward. Using std::function or boost::signal2 and a little bit of more complication better ad-hoc callback management can be achieved. But I guess you just need some starter. A shorter solution is none-capture lambda:

void Controller::nextStep(Fl_Widget *);

o->callback(
    [](Fl_Widget *w, void *that){
        reinterpret_cast<Controller*>(that)->nextStep(w);
    }
,this);

非捕获 lambda - 按照惯例 - 衰减为具有兼容签名的自由函数指针.这个解决方案更简单，但模板将潜在风险的转换封装在一个类中，以减少出现错误的机会.

a none-capture lambda - by convention - decays to a free function pointer with compatible signature. This solution is simpler but the template one encapsulates the potentially risky cast in a class in order to decrease the chances for bugs.

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