Linux Nested Sub Menu

[cranst0n]

I had a need to have a menu on Linux with a menu with a sub menu nested inside a sub menu. I'm not proficient in C++ so after I fumbled around for a while, I ultimately came up with this solution. I'll let it in this issue since I doubt this hackery is worthy of a PR. All edits were made inside native_context_menu_plugin_handle_method_call:

static void native_context_menu_plugin_handle_method_call(
    NativeContextMenuPlugin* self, FlMethodCall* method_call) {
  g_autoptr(FlMethodResponse) response = nullptr;
  const gchar* method = fl_method_call_get_name(method_call);
  if (strcmp(method, kShowMenu) == 0) {
    // Clear previously saved object instances.
    self->last_menu_items.clear();
    self->last_menu_item_selected = false;
    if (self->last_menu_thread != nullptr) {
      self->last_menu_thread->detach();
      self->last_menu_thread.reset(nullptr);
    }
    auto arguments = fl_method_call_get_args(method_call);
    auto device_pixel_ratio =
        fl_value_lookup_string(arguments, "devicePixelRatio");

    auto position = fl_value_lookup_string(arguments, "position");

    GdkWindow* window = get_window(self);

    GtkWidget* top_level_menu = gtk_menu_new();
    auto top_level_items = fl_value_lookup_string(arguments, "items");

    for (int32_t i = 0; i < fl_value_get_length(top_level_items); i++) {

      int32_t top_level_id = fl_value_get_int(
          fl_value_lookup_string(fl_value_get_list_value(top_level_items, i), "id"));
      const char* top_level_title = fl_value_get_string(
          fl_value_lookup_string(fl_value_get_list_value(top_level_items, i), "title"));

      auto second_level_items =
          fl_value_lookup_string(fl_value_get_list_value(top_level_items, i), "items");

      self->last_menu_items.emplace_back(std::make_unique<MenuItem>(top_level_id, top_level_title));

      GtkWidget* top_level_item = gtk_menu_item_new_with_label(top_level_title);

      // Check for second level items & create a second level menu.
      if (fl_value_get_length(second_level_items) > 0) {

        GtkWidget* second_level_menu = gtk_menu_new();

        for (int32_t j = 0; j < fl_value_get_length(second_level_items); j++) {

          int32_t second_level_id = fl_value_get_int(fl_value_lookup_string(
              fl_value_get_list_value(second_level_items, j), "id"));
          const char* second_level_title = fl_value_get_string(fl_value_lookup_string(
              fl_value_get_list_value(second_level_items, j), "title"));

          auto third_level_items =
            fl_value_lookup_string(fl_value_get_list_value(second_level_items, j), "items");

          self->last_menu_items.back()->items().emplace_back(
              std::make_unique<MenuItem>(second_level_id, second_level_title));

          GtkWidget* second_level_item = gtk_menu_item_new_with_label(second_level_title);

          // Check for third level items & create a third level menu.
          if (fl_value_get_length(third_level_items) > 0) {
            GtkWidget* third_level_menu = gtk_menu_new();

            for (int32_t k = 0; k < fl_value_get_length(third_level_items); k++) {

              int32_t third_level_id = fl_value_get_int(fl_value_lookup_string(
                  fl_value_get_list_value(third_level_items, k), "id"));
              const char* third_level_title = fl_value_get_string(fl_value_lookup_string(
                  fl_value_get_list_value(third_level_items, k), "title"));

              self->last_menu_items.back()->items().back()->items().emplace_back(
                std::make_unique<MenuItem>(third_level_id, third_level_title));

              GtkWidget* third_level_item = gtk_menu_item_new_with_label(third_level_title);

              gtk_widget_show(third_level_item);
              gtk_menu_shell_append(GTK_MENU_SHELL(third_level_menu), third_level_item);

              g_signal_connect(
                  G_OBJECT(third_level_item), "activate",
                  G_CALLBACK(on_menu_item_clicked),
                  (gpointer)self->last_menu_items.back()->items().at(j).get()->items().at(k).get());
            }

            gtk_menu_item_set_submenu(GTK_MENU_ITEM(second_level_item), third_level_menu);

          } else {
            g_signal_connect(G_OBJECT(second_level_item), "activate",
                            G_CALLBACK(on_menu_item_clicked),
                            (gpointer)self->last_menu_items.back()->items().at(j).get());
          }

          gtk_widget_show(second_level_item);
          gtk_menu_shell_append(GTK_MENU_SHELL(second_level_menu), second_level_item);

        }

        gtk_menu_item_set_submenu(GTK_MENU_ITEM(top_level_item), second_level_menu);

      } else {
        g_signal_connect(G_OBJECT(top_level_item), "activate",
                         G_CALLBACK(on_menu_item_clicked),
                         (gpointer)self->last_menu_items.back().get());
      }

      gtk_widget_show(top_level_item);
      gtk_menu_shell_append(GTK_MENU_SHELL(top_level_menu), top_level_item);
    }

    GdkRectangle rectangle;
    // Pass `devicePixelRatio` and `position` from Dart to show menu at
    // specified coordinates. If it is not defined, WIN32 will use
    // `GetCursorPos` to show the context menu at the cursor's position.
    if (device_pixel_ratio != nullptr && position != nullptr) {
      rectangle.x = fl_value_get_float(fl_value_get_list_value(position, 0)) *
                    fl_value_get_float(device_pixel_ratio);
      rectangle.y = fl_value_get_float(fl_value_get_list_value(position, 1)) *
                    fl_value_get_float(device_pixel_ratio);
    } else {
      GdkDevice* mouse_device;
      int x, y;
      // Legacy support.
#if GTK_CHECK_VERSION(3, 20, 0)
      GdkSeat* seat = gdk_display_get_default_seat(gdk_display_get_default());
      mouse_device = gdk_seat_get_pointer(seat);
#else
      GdkDeviceManager* devman =
          gdk_display_get_device_manager(gdk_display_get_default());
      mouse_device = gdk_device_manager_get_client_pointer(devman);
#endif
      gdk_window_get_device_position(window, mouse_device, &x, &y, NULL);
      rectangle.x = x;
      rectangle.y = y;
    }
    g_signal_connect(G_OBJECT(top_level_menu), "deactivate",
                     G_CALLBACK(on_menu_deactivated), nullptr);
    // `gtk_menu_popup_at_rect` is used since `gtk_menu_popup_at_pointer` will
    // require event box creation & another callback will be involved. This way
    // is straight forward & easy to work with.
    // NOTE: GDK_GRAVITY_NORTH_WEST is hard-coded by default since no analog is
    // present for it inside the Dart platform channel code (as of now). In
    // summary, this will create a menu whose body is in bottom-right to the
    // position of the mouse pointer.
    gtk_menu_popup_at_rect(GTK_MENU(top_level_menu), window, &rectangle,
                           GDK_GRAVITY_NORTH_WEST, GDK_GRAVITY_NORTH_WEST,
                           NULL);

    // Responding with `null`, click event & respective `id` of the `MenuItem`
    // is notified through callback. Otherwise the GUI will become unresponsive.
    // To keep the API same, a `Completer` is used in the Dart.
    response =
        FL_METHOD_RESPONSE(fl_method_success_response_new(fl_value_new_null()));
  } else {
    response = FL_METHOD_RESPONSE(fl_method_not_implemented_response_new());
  }
  fl_method_call_respond(method_call, response, nullptr);
}