update.rs

Finally we have the update.rs file. Here, the update() function takes in two arguments:

key_event: This is an event provided by the crossterm crate, representing a key press from the user.
app: A mutable reference to our application’s state, represented by the App struct.

use crossterm::event::{KeyCode, KeyEvent, KeyModifiers};

use crate::app::App;

pub fn update(app: &mut App, key_event: KeyEvent) {
    match key_event.code {
        KeyCode::Esc | KeyCode::Char('q') => app.quit(),
        KeyCode::Char('c') | KeyCode::Char('C') => {
            if key_event.modifiers == KeyModifiers::CONTROL {
                app.quit()
            }
        }
        KeyCode::Right | KeyCode::Char('j') => app.increment_counter(),
        KeyCode::Left | KeyCode::Char('k') => app.decrement_counter(),
        _ => {}
    };
}

Note that here we don’t have to check that key_event.kind is KeyEventKind::Press because we already do that check in event.rs and only send KeyEventKind::Press events on the channel.