Encapsulate widgets with rust logic

[John0x]

Hey, I've read the documentation and examples, but couldn't quite figure out what the proper approach for more complex applications looks like. Let's say, that I have some application with multiple screens using Rust. From what I understand, if I want to add some logic using rust, I have to do it via callbacks on the window? Is there no way to create a widget using the slint language, add some logic using rust and then use that Widget, with the rust logic, within another slint language widget/window?

Having a single point to add the rust logic feels extremely inconvenient to me. I would have imagined something like this: (pseudocode):

pub fn MyLoginScreen() {
    slint::slint! {
        import { Button } from "std-widgets.slint";

        export LoginScreen := Rectangle {
            callback login_clicked <=> btnLogin.clicked;

            HorizontalLayout {
                alignment: center;
                VerticalLayout {
                    alignment: center;
                    btnLogin := Button {
                        text: "Login";
                    }
                }
            }
        }
    }

    let login = LoginScreen::new();
    login.on_login_clicked(|| eprintln!("LOGIN"));
}


pub fn main() {
    slint::slint! {
        export App := Window {
            callback quit();
            login := MyLoginScreen {  }
        }
    }

    let app = App::new();
    app.run();
}

Is adding the logic via callbacks to the window and then forwarding these to the screens the only way?