Listen to events

Often you want to do something when the user presses some key, if a file is dropped on your window or general mouse events. For that, you can use the iced::event::listen subscription. It runs in the background and emits a message with/on every Event.

NOTE: If you just want to get mouse events in a specific widget area you should use the MouseArea widget.

Here is a practical example how to listen to an arbitrary event in form of a keyboard event.

In the example, the subscription always runs as defined in the Application::subscription method:

use iced::widget;

#[derive(Debug, Clone)]
enum Message {
    Event(iced::event::Event),
}

fn update(state: &mut u32, message: Message) {
    // handle emitted messages
    match message {
        Message::Event(event) => {
            if let iced::event::Event::Keyboard(iced::keyboard::Event::KeyReleased {
                key, ..
            }) = event
            {
                println!("Key {key:?} was pressed");
                *state += 1;
            }
        }
    }
}

fn view(state: &u32) -> iced::Element<'_, Message> {
    widget::text!("Keys pressed: {}", state).into()
}

fn main() -> iced::Result {
    // run the app from main function
    iced::application(|| 0, update, view)
        .subscription(|_state| iced::event::listen().map(Message::Event))
        .run()
}

It emits a message containing the event:

use iced::widget;

#[derive(Debug, Clone)]
enum Message {
    Event(iced::event::Event),
}

fn update(state: &mut u32, message: Message) {
    // handle emitted messages
    match message {
        Message::Event(event) => {
            if let iced::event::Event::Keyboard(iced::keyboard::Event::KeyReleased {
                key, ..
            }) = event
            {
                println!("Key {key:?} was pressed");
                *state += 1;
            }
        }
    }
}

fn view(state: &u32) -> iced::Element<'_, Message> {
    widget::text!("Keys pressed: {}", state).into()
}

fn main() -> iced::Result {
    // run the app from main function
    iced::application(|| 0, update, view)
        .subscription(|_state| iced::event::listen().map(Message::Event))
        .run()
}

In the update method we can use that event and react to it:

use iced::widget;

#[derive(Debug, Clone)]
enum Message {
    Event(iced::event::Event),
}

fn update(state: &mut u32, message: Message) {
    // handle emitted messages
    match message {
        Message::Event(event) => {
            if let iced::event::Event::Keyboard(iced::keyboard::Event::KeyReleased {
                key, ..
            }) = event
            {
                println!("Key {key:?} was pressed");
                *state += 1;
            }
        }
    }
}

fn view(state: &u32) -> iced::Element<'_, Message> {
    widget::text!("Keys pressed: {}", state).into()
}

fn main() -> iced::Result {
    // run the app from main function
    iced::application(|| 0, update, view)
        .subscription(|_state| iced::event::listen().map(Message::Event))
        .run()
}

Important Note: The example uses iced::event::listen that reacts to all kind of events. There are specific subscriptions for special event kinds, such as window, and keyboard events.

Full Code

use iced::widget;

#[derive(Debug, Clone)]
enum Message {
    Event(iced::event::Event),
}

fn update(state: &mut u32, message: Message) {
    // handle emitted messages
    match message {
        Message::Event(event) => {
            if let iced::event::Event::Keyboard(iced::keyboard::Event::KeyReleased {
                key, ..
            }) = event
            {
                println!("Key {key:?} was pressed");
                *state += 1;
            }
        }
    }
}

fn view(state: &u32) -> iced::Element<'_, Message> {
    widget::text!("Keys pressed: {}", state).into()
}

fn main() -> iced::Result {
    // run the app from main function
    iced::application(|| 0, update, view)
        .subscription(|_state| iced::event::listen().map(Message::Event))
        .run()
}