Tutorial 3 - Async Tasks

Official examples (todos, events, clock, websocket) show the same rule: async and external events still flow through typed messages.

# Use this when...

• You need API/file/network work that should not block UI.
• You need periodic or external event streams.
• You want predictable side effects in a reactive app.

# Minimal example

fn update(state: &mut App, message: Message) -> iced::Task<Message> {
    match message {
        Message::LoadRequested => iced::Task::perform(load_data(), Message::Loaded),
        Message::Loaded(data) => {
            state.data = data;
            iced::Task::none()
        }
    }
}

# How it works

Task is for one-shot effects started by user/runtime events. Subscription is for continuous streams you want active while a state condition is true.

# Common patterns

fn subscription(state: &App) -> iced::Subscription<Message> {
    if state.live_updates {
        iced::time::every(std::time::Duration::from_secs(1)).map(Message::Tick)
    } else {
        iced::Subscription::none()
    }
}

# Gotchas / tips

• Always map async outcomes into your Message enum.
• Disable subscriptions when not needed to avoid extra work.
• Keep task creation in update; do not trigger effects directly from view.

# Next

• Tutorial 4 - Theming and Components
• Tasks and Subscriptions