Making vector of Buttons using FlTK with c++ - c++

Question

I am supposed to make the game called 15 sliding puzzle where you click a button, the callback function moves it. Right I am trying to make the board by making a vector or array of but I am confused on how I Would do that. I don't know how to make a vector of Buttons and attach them to the window. he attach() is for attaching a single element so I don't know how I would use it with a vecto
Here is my header file
#ifndef LevelOne_h
#define LevelOne_h
#include "GUI.h"
#include "Graph.h"
#include <FL/Fl_JPEG_Image.H>
#include<vector>
using namespace Graph_lib;
//-----------------------------------------------------------------------------
class Level_One : Graph_lib::Window {
public:
Level_One(Point xy, int w, int h, const string& title);
private:
vector<Button> Trial_button;
static void cb_trial(Address, Address);
void trial();
};
#endif /* LevelOne_h */
And here is my .cpp file
#include "LevelOne.h"
Level_One::Level_One(Point xy, int w, int h, const string& title)
:Window{xy,w,h,title} ,
Trial_button{Point{150,150},100,100,"TRIAL",cb_trial}
{
attach(Trial_button);
}
void Level_One::cb_trial(Address,Address pw)
{
reference_to<Level_One>(pw).trial();
}
void Level_One::trial()
{
hide();
}
//-----------------------------------------------------------------------------
int main ()
try{
Level_One win {Point{100,100},500,500,"The Sliding Tiles Puzzle"};
return gui_main();
}
catch (exception& e){ //catches range errors and run_time_errors
cerr << "error: "<< e.what() <<'\n';
return 1;
}
catch (...){ //catch any exception
cerr <<"Exception: something went wrong \n";
return 2;
}