Gtkmm, 4.0 Program terminate Error: Unhandled tag: <cambalache-project>

Hi, i am a beginner and trying a first Hello world project. Following the gtkmm 4 guide i get a basic app to work.

But when using a Cambalache gui definition file i get the error. Im using Fedora.

terminate called after throwing an instance of ‘Gtk::BuilderError’
what(): 4:1 Unhandled tag:

#include <gtkmm.h>

class MyWindow : public Gtk::Window

    set_title("Basic application");

int main(int argc, char *argv[])

    auto app {Gtk::Application::create("org.gtkmm.examples.base")};

    auto builder {Gtk::Builder::create_from_file("/home/ello/misc/CLionProjects/non_template/src/myui.cmb")};

    return app->make_window_and_run<MyWindow>(argc, argv);
<?xml version='1.0' encoding='UTF-8' standalone='no'?>
<!DOCTYPE cambalache-project SYSTEM "cambalache-project.dtd">
<cambalache-project version="0.17.3" target_tk="gtk-4.0">
	(1,None,"hello world.ui","hello world.ui",None,None,None,None,None,None,None)

You cannot use a Cambalache file with Gtk::Builder: they are not the same thing; the cmb file is a Cambalache project file.

You’ll need to tell Cambalache to generates the GtkBuilder XML, and then load that file.

yes, works!
I have some opinions on Cambalache…

Is there any alternatives?

You mean: are there other UI design tools for GTK4? The answer is, currently, no: there’s only Cambalache.

Many developers don’t use UI design tools, though, and write the UI by hand—either by writing UI templates, which are not supported by gtkmm; or by using Blueprint, which “compiles” to XML at build time.

If you have opinions about Cambalache, feel free to join the cambalache room on Matrix.