Listen to the keyboard events with Rust and GTK

I found Rust GTK documentation pretty weird. Maybe I’m wrong. I hope so. But it looks like that.
Ok. Here is the piece of code. It can listen to keyboard events and print keys combinations it terminal: “Key name” and “Modifier” (for example Shift key). And values[1] is our keyboard event

window
    .connect("key_press_event", false, |values| {
        let raw_event = &values[1].get::<gdk::Event>().unwrap();
        match raw_event.downcast_ref::<gdk::EventKey>() {
            Some(event) => {
                println!("Key name: {:?}", event.keyval());
                println!("Modifier: {:?}", event.state());
            },
            None => {},
        }

        let result = glib::value::Value::from_type(glib::types::Type::BOOL);
        Some(result)
    });

I have to figure out how it works. And then put it into practice, for example add this functionality to my GTK calculator.

Cargo.toml

[dependencies]
glib = "0.15.12"
gdk = "0.15.4"
gtk = "0.15.5"

main.rs

use gtk::prelude::*;
mod gui;

fn main() {
    let application = gtk::Application::new(
        Some("com.github.gtk-rs.gtk_keyboard_events_listener"),
        Default::default(),
    );
    application.connect_activate(gui::build_ui);
    application.run();
}

Permanent link to the gui.rs file