Struct bevy::ecs::event::ManualEventReader

pub struct ManualEventReader<E>
where
    E: Event,
{ /* private fields */ }

Stores the state for an EventReader.

Access to the Events<E> resource is required to read any incoming events.

In almost all cases, you should just use an EventReader, which will automatically manage the state for you.

However, this type can be useful if you need to manually track events, such as when you’re attempting to send and receive events of the same type in the same system.

Example

use bevy_ecs::prelude::*;
use bevy_ecs::event::{Event, Events, ManualEventReader};

#[derive(Event, Clone, Debug)]
struct MyEvent;

/// A system that both sends and receives events using a [`Local`] [`ManualEventReader`].
fn send_and_receive_manual_event_reader(
    // The `Local` `SystemParam` stores state inside the system itself, rather than in the world.
    // `ManualEventReader<T>` is the internal state of `EventReader<T>`, which tracks which events have been seen.
    mut local_event_reader: Local<ManualEventReader<MyEvent>>,
    // We can access the `Events` resource mutably, allowing us to both read and write its contents.
    mut events: ResMut<Events<MyEvent>>,
) {
    // We must collect the events to resend, because we can't mutate events while we're iterating over the events.
    let mut events_to_resend = Vec::new();

    for event in local_event_reader.read(&events) {
         events_to_resend.push(event.clone());
    }

    for event in events_to_resend {
        events.send(MyEvent);
    }
}

Implementations

impl<E> ManualEventReader<E>

where E: Event,

pub fn read<'a>(&'a mut self, events: &'a Events<E>) -> EventIterator<'a, E>

See EventReader::read

Examples found in repository

examples/ecs/send_and_receive_events.rs (line 153)

fn send_and_receive_manual_event_reader(
    // The `Local` `SystemParam` stores state inside the system itself, rather than in the world.
    // `ManualEventReader<T>` is the internal state of `EventReader<T>`, which tracks which events have been seen.
    mut local_event_reader: Local<ManualEventReader<DebugEvent>>,
    // We can access the `Events` resource mutably, allowing us to both read and write its contents.
    mut events: ResMut<Events<DebugEvent>>,
    frame_count: Res<FrameCount>,
) {
    println!(
        "Sending and receiving events for frame {} with a `Local<ManualEventReader>",
        frame_count.0
    );

    // We must collect the events to resend, because we can't mutate events while we're iterating over the events.
    let mut events_to_resend = Vec::new();

    for event in local_event_reader.read(&events) {
        if event.resend_from_local_event_reader {
            // For simplicity, we're cloning the event.
            // In this case, since we have mutable access to the `Events` resource,
            // we could also just mutate the event in-place,
            // or drain the event queue into our `events_to_resend` vector.
            events_to_resend.push(event.clone());
        }
    }

    for mut event in events_to_resend {
        event.times_sent += 1;
        events.send(event);
    }
}

pub fn read_with_id<'a>( &'a mut self, events: &'a Events<E> ) -> EventIteratorWithId<'a, E>

See EventReader::read_with_id

pub fn par_read<'a>(&'a mut self, events: &'a Events<E>) -> EventParIter<'a, E>

See EventReader::par_read

pub fn len(&self, events: &Events<E>) -> usize

See EventReader::len

pub fn missed_events(&self, events: &Events<E>) -> usize

Amount of events we missed.

pub fn is_empty(&self, events: &Events<E>) -> bool

See EventReader::is_empty()

pub fn clear(&mut self, events: &Events<E>)

See EventReader::clear()

Trait Implementations

impl<E> Clone for ManualEventReader<E>

where E: Event,

fn clone(&self) -> ManualEventReader<E>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<E> Debug for ManualEventReader<E>

where E: Debug + Event,

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<E> Default for ManualEventReader<E>

where E: Event,

fn default() -> ManualEventReader<E>

Returns the “default value” for a type.