Using gtk::Application

Before we begin, we need to add some utility functions that we'll be using throughout the application. We will be spawning a background thread and executing tasks on it, so we'll need a convenience function for fetching the thread-default context. Likewise, we're going to spawning tasks on the global default context, so we'll need that here as well.

fn main() {
use std::future::Future;

pub fn thread_context() -> glib::MainContext {
        .unwrap_or_else(|| {
            let ctx = glib::MainContext::new();

pub fn spawn<F>(future: F) where F: Future<Output = ()> + 'static {

This time we will create a GTK application using the proper gtk::Application setup process. This will take care of initializing GTK for you, and registers your application with an application ID so that you can prevent your application from spawning multiple instances.

extern crate cascade;

mod app;
mod background;
mod widgets;
mod utils;

use self::app::App;
use gio::prelude::*;

/// The name that we will register to the system to identify our application
pub const APP_ID: &str = "io.github.mmstick.ToDo";

fn main() {
    let app_name = "Todo";


    // Initializes GTK and registers our application. gtk::Application helps us
    // set up an application with less work
    let app = gtk::Application::new(
    ).expect("failed to init application");

    // After the application has been registered, it will trigger an activate
    // signal, which will give us the okay to construct our application and set
    // up our application logic. We're going to use `app` to create the
    // application window in the future.
    app.connect_activate(|app| {
        let (tx, rx) = async_channel::unbounded();

        let mut app = App::new(app, tx);

        let event_handler = async move {
            while let Ok(event) = rx.recv().await {
                match event {



    // This last step performs the same duty as gtk::main()[]);

Calling gtk::Application::new() will run gtk::init() and register your application by the APP_ID that we defined. The general practice for application IDs is to use Reverse domain name notation (RDNN). gtk::Application::connect_activate() signals that GTK is ready for us to construct our application window and set up all of our application logic. This method receives a reference to the gtk::Application itself, which we will later use to create the gtk::ApplicationWindow, which is our top level gtk::Window for our application. gtk::Application::run() will then invoke gtk::main() to set the whole process in motion.