Gtk::Builder.get_object always returns NULL
This code returns NULL and cast error:
auto btnBox = builder->get_object("ButtonBox");
gtk_widget_set_size_request(GTK_WIDGET(btnBox.get()), w, h);
Error:
GLib-GObject-WARNING **: 19:23:27.978: invalid uninstantiatable type '(NULL)' in cast to 'GtkWidget'
Gtk-CRITICAL **: 19:23:27.983: gtk_widget_set_size_request: assertion 'GTK_IS_WIDGET (widget)' failed
C version works fine:
auto btnBox = GTK_WIDGET(gtk_builder_get_object(builder->gobj(), "ButtonBox"));
gtk_widget_set_size_request(btnBox, w, h);
GTK and GTKMM version are both 3.24.2-1