main.rs

use chrono::Local;
use gtk::glib;
use gtk::prelude::*;

fn current_time() -> String {
    format!("{}", Local::now().format("%Y-%m-%d %H:%M:%S"))
}

fn build_ui(application: &gtk::Application) {
    let window = gtk::ApplicationWindow::new(application);

    window.set_title("First GTK+ Clock");
    window.set_border_width(10);
    window.set_position(gtk::WindowPosition::Center);
    window.set_default_size(260, 40);

    let time = current_time();
    let label = gtk::Label::new(None);
    label.set_text(&time);

    window.add(&label);

    window.show_all();

    // we are using a closure to capture the label (else we could also use a normal function)
    let tick = move || {
        let time = current_time();
        label.set_text(&time);
        // we could return glib::ControlFlow::Break to stop our clock after this tick
        glib::ControlFlow::Continue
    };

    // executes the closure once every second
    glib::timeout_add_seconds_local(1, tick);
}

fn main() {
    let application =
        gtk::Application::new(Some("com.github.gtk-rs.examples.clock"), Default::default());

    application.connect_activate(build_ui);

    application.run();
}