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//! Listen to external events in your application.
use crate::event::{self, Event};
use crate::window;
use crate::Hasher;
use iced_futures::futures::channel::mpsc;
use iced_futures::futures::never::Never;
use iced_futures::futures::{self, Future, Stream};
use iced_futures::{BoxStream, MaybeSend};
use std::hash::Hash;
/// A request to listen to external events.
///
/// Besides performing async actions on demand with [`Command`], most
/// applications also need to listen to external events passively.
///
/// A [`Subscription`] is normally provided to some runtime, like a [`Command`],
/// and it will generate events as long as the user keeps requesting it.
///
/// For instance, you can use a [`Subscription`] to listen to a WebSocket
/// connection, keyboard presses, mouse events, time ticks, etc.
///
/// [`Command`]: crate::Command
pub type Subscription<T> =
iced_futures::Subscription<Hasher, (Event, event::Status), T>;
/// A stream of runtime events.
///
/// It is the input of a [`Subscription`] in the native runtime.
pub type EventStream = BoxStream<(Event, event::Status)>;
/// A native [`Subscription`] tracker.
pub type Tracker =
iced_futures::subscription::Tracker<Hasher, (Event, event::Status)>;
pub use iced_futures::subscription::Recipe;
/// Returns a [`Subscription`] to all the ignored runtime events.
///
/// This subscription will notify your application of any [`Event`] that was
/// not captured by any widget.
pub fn events() -> Subscription<Event> {
events_with(|event, status| match status {
event::Status::Ignored => Some(event),
event::Status::Captured => None,
})
}
/// Returns a [`Subscription`] that filters all the runtime events with the
/// provided function, producing messages accordingly.
///
/// This subscription will call the provided function for every [`Event`]
/// handled by the runtime. If the function:
///
/// - Returns `None`, the [`Event`] will be discarded.
/// - Returns `Some` message, the `Message` will be produced.
pub fn events_with<Message>(
f: fn(Event, event::Status) -> Option<Message>,
) -> Subscription<Message>
where
Message: 'static + MaybeSend,
{
#[derive(Hash)]
struct EventsWith;
Subscription::from_recipe(Runner {
id: (EventsWith, f),
spawn: move |events| {
use futures::future;
use futures::stream::StreamExt;
events.filter_map(move |(event, status)| {
future::ready(match event {
Event::Window(window::Event::RedrawRequested(_)) => None,
_ => f(event, status),
})
})
},
})
}
pub(crate) fn raw_events<Message>(
f: fn(Event, event::Status) -> Option<Message>,
) -> Subscription<Message>
where
Message: 'static + MaybeSend,
{
#[derive(Hash)]
struct RawEvents;
Subscription::from_recipe(Runner {
id: (RawEvents, f),
spawn: move |events| {
use futures::future;
use futures::stream::StreamExt;
events.filter_map(move |(event, status)| {
future::ready(f(event, status))
})
},
})
}
/// Returns a [`Subscription`] that will call the given function to create and
/// asynchronously run the given [`Stream`].
pub fn run<S, Message>(builder: fn() -> S) -> Subscription<Message>
where
S: Stream<Item = Message> + MaybeSend + 'static,
Message: 'static,
{
Subscription::from_recipe(Runner {
id: builder,
spawn: move |_| builder(),
})
}
/// Returns a [`Subscription`] that will create and asynchronously run the
/// given [`Stream`].
///
/// The `id` will be used to uniquely identify the [`Subscription`].
pub fn run_with_id<I, S, Message>(id: I, stream: S) -> Subscription<Message>
where
I: Hash + 'static,
S: Stream<Item = Message> + MaybeSend + 'static,
Message: 'static,
{
Subscription::from_recipe(Runner {
id,
spawn: move |_| stream,
})
}
/// Returns a [`Subscription`] that will create and asynchronously run a
/// [`Stream`] that will call the provided closure to produce every `Message`.
///
/// The `id` will be used to uniquely identify the [`Subscription`].
pub fn unfold<I, T, Fut, Message>(
id: I,
initial: T,
mut f: impl FnMut(T) -> Fut + MaybeSend + Sync + 'static,
) -> Subscription<Message>
where
I: Hash + 'static,
T: MaybeSend + 'static,
Fut: Future<Output = (Message, T)> + MaybeSend + 'static,
Message: 'static + MaybeSend,
{
use futures::future::FutureExt;
run_with_id(
id,
futures::stream::unfold(initial, move |state| f(state).map(Some)),
)
}
/// Creates a [`Subscription`] that publishes the events sent from a [`Future`]
/// to an [`mpsc::Sender`] with the given bounds.
///
/// # Creating an asynchronous worker with bidirectional communication
/// You can leverage this helper to create a [`Subscription`] that spawns
/// an asynchronous worker in the background and establish a channel of
/// communication with an `iced` application.
///
/// You can achieve this by creating an `mpsc` channel inside the closure
/// and returning the `Sender` as a `Message` for the `Application`:
///
/// ```
/// use iced_native::subscription::{self, Subscription};
/// use iced_native::futures::channel::mpsc;
/// use iced_native::futures::sink::SinkExt;
///
/// pub enum Event {
/// Ready(mpsc::Sender<Input>),
/// WorkFinished,
/// // ...
/// }
///
/// enum Input {
/// DoSomeWork,
/// // ...
/// }
///
/// enum State {
/// Starting,
/// Ready(mpsc::Receiver<Input>),
/// }
///
/// fn some_worker() -> Subscription<Event> {
/// struct SomeWorker;
///
/// subscription::channel(std::any::TypeId::of::<SomeWorker>(), 100, |mut output| async move {
/// let mut state = State::Starting;
///
/// loop {
/// match &mut state {
/// State::Starting => {
/// // Create channel
/// let (sender, receiver) = mpsc::channel(100);
///
/// // Send the sender back to the application
/// output.send(Event::Ready(sender)).await;
///
/// // We are ready to receive messages
/// state = State::Ready(receiver);
/// }
/// State::Ready(receiver) => {
/// use iced_native::futures::StreamExt;
///
/// // Read next input sent from `Application`
/// let input = receiver.select_next_some().await;
///
/// match input {
/// Input::DoSomeWork => {
/// // Do some async work...
///
/// // Finally, we can optionally produce a message to tell the
/// // `Application` the work is done
/// output.send(Event::WorkFinished).await;
/// }
/// }
/// }
/// }
/// }
/// })
/// }
/// ```
///
/// Check out the [`websocket`] example, which showcases this pattern to maintain a WebSocket
/// connection open.
///
/// [`websocket`]: https://github.com/iced-rs/iced/tree/0.9/examples/websocket
pub fn channel<I, Fut, Message>(
id: I,
size: usize,
f: impl Fn(mpsc::Sender<Message>) -> Fut + MaybeSend + Sync + 'static,
) -> Subscription<Message>
where
I: Hash + 'static,
Fut: Future<Output = Never> + MaybeSend + 'static,
Message: 'static + MaybeSend,
{
use futures::stream::{self, StreamExt};
Subscription::from_recipe(Runner {
id,
spawn: move |_| {
let (sender, receiver) = mpsc::channel(size);
let runner = stream::once(f(sender)).map(|_| unreachable!());
stream::select(receiver, runner)
},
})
}
struct Runner<I, F, S, Message>
where
F: FnOnce(EventStream) -> S,
S: Stream<Item = Message>,
{
id: I,
spawn: F,
}
impl<I, S, F, Message> Recipe<Hasher, (Event, event::Status)>
for Runner<I, F, S, Message>
where
I: Hash + 'static,
F: FnOnce(EventStream) -> S,
S: Stream<Item = Message> + MaybeSend + 'static,
{
type Output = Message;
fn hash(&self, state: &mut Hasher) {
std::any::TypeId::of::<I>().hash(state);
self.id.hash(state);
}
fn stream(self: Box<Self>, input: EventStream) -> BoxStream<Self::Output> {
iced_futures::boxed_stream((self.spawn)(input))
}
}