folder_tree_nana.cpp

#include <nana/deploy.hpp>
#include <nana/gui.hpp>
#include <nana/gui/widgets/treebox.hpp>

//#define NANA_FILESYSTEM_FORCE      // if used this way, make sure nana was compiled with this option too
#include <nana/filesystem/filesystem_ext.hpp>

int main()
{
        using namespace nana;
        namespace fs = std::filesystem;
        namespace fs_ext = nana::filesystem_ext;
        using dir_it = fs_ext::directory_only_iterator;

        form fm{ API::make_center(400, 500), appear::decorate<appear::taskbar>() };
        fm.caption("Nana C++ Library - Treebox-nana::filesystem example.");
        nana::treebox tree{ fm, { 10, 10, 380, 480 } };
    
        auto node = tree.insert(fs_ext::def_root, fs_ext::def_rootname);

        // Boost can throw an exception "Access is denied"
        // when accessing some system paths, like "C:\Config.Msi"
   try {
        dir_it sub_root{ fs_ext::def_rootstr};
        auto p = sub_root->path();
        std::string dir_name= p.filename().generic_string();
        tree.insert(node, dir_name,dir_name);
        } catch (...) {}

        tree.events().expanded([&tree](const arg_treebox& arg)
        {
                if (!arg.operated) return; //If this is contracted.

                //Windows supports the path separator '/'
                auto Path = tree.make_key_path(arg.item, "/") + "/";

                //avoids frequent useless refreshing
                tree.auto_draw(false);

        try {
                //Walk in the path directory for sub directories.
                for (const auto& dir : dir_it{ Path })
                {
                        std::string dir_name= dir.path().filename().generic_string();

                        auto child = tree.insert(arg.item, dir_name, dir_name);
                        if (child.empty()) continue;   // ?

                        //Find a directory in child directory, if there is a directory,
                        //insert it into the child, just insert one node to indicate the
                        //node has a child and an arrow symbol will be?displayed in the
                        //front of the node.
                try {
                        dir_it d{ dir.path() };
                        if (d != dir_it{})
                        {
                                std::string sdir_name = d->path().filename().generic_string();
                                tree.insert(child, sdir_name, sdir_name);
                        }
                        } catch (...) {}
                }
                } catch (...) {}
                tree.auto_draw(true);
        });

        fm.show();
        exec(

#ifdef NANA_AUTOMATIC_GUI_TESTING
                2, 1, [&node]()
        {
                node.expand(true);
        }
#endif

        );
}