pub struct EventReader<'w, 's, E: Event> { /* private fields */ }
Expand description
Reads events of type T
in order and tracks which events have already been read.
§Concurrency
Unlike EventWriter<T>
, systems with EventReader<T>
param can be executed concurrently
(but not concurrently with EventWriter<T>
systems for the same event type).
Implementations§
Source§impl<'w, 's, E: Event> EventReader<'w, 's, E>
impl<'w, 's, E: Event> EventReader<'w, 's, E>
Sourcepub fn read(&mut self) -> EventIterator<'_, E> ⓘ
pub fn read(&mut self) -> EventIterator<'_, E> ⓘ
Iterates over the events this EventReader
has not seen yet. This updates the
EventReader
’s event counter, which means subsequent event reads will not include events
that happened before now.
Sourcepub fn read_with_id(&mut self) -> EventIteratorWithId<'_, E> ⓘ
pub fn read_with_id(&mut self) -> EventIteratorWithId<'_, E> ⓘ
Sourcepub fn par_read(&mut self) -> EventParIter<'_, E>
pub fn par_read(&mut self) -> EventParIter<'_, E>
Returns a parallel iterator over the events this EventReader
has not seen yet.
See also for_each
.
§Example
#[derive(Event)]
struct MyEvent {
value: usize,
}
#[derive(Resource, Default)]
struct Counter(AtomicUsize);
// setup
let mut world = World::new();
world.init_resource::<Events<MyEvent>>();
world.insert_resource(Counter::default());
let mut schedule = Schedule::default();
schedule.add_systems(|mut events: EventReader<MyEvent>, counter: Res<Counter>| {
events.par_read().for_each(|MyEvent { value }| {
counter.0.fetch_add(*value, Ordering::Relaxed);
});
});
for value in 0..100 {
world.send_event(MyEvent { value });
}
schedule.run(&mut world);
let Counter(counter) = world.remove_resource::<Counter>().unwrap();
// all events were processed
assert_eq!(counter.into_inner(), 4950);
Sourcepub fn len(&self) -> usize
pub fn len(&self) -> usize
Determines the number of events available to be read from this EventReader
without consuming any.
Sourcepub fn is_empty(&self) -> bool
pub fn is_empty(&self) -> bool
Returns true
if there are no events available to read.
§Example
The following example shows a useful pattern where some behavior is triggered if new events are available.
EventReader::clear()
is used so the same events don’t re-trigger the behavior the next time the system runs.
#[derive(Event)]
struct CollisionEvent;
fn play_collision_sound(mut events: EventReader<CollisionEvent>) {
if !events.is_empty() {
events.clear();
// Play a sound
}
}
Sourcepub fn clear(&mut self)
pub fn clear(&mut self)
Consumes all available events.
This means these events will not appear in calls to EventReader::read()
or
EventReader::read_with_id()
and EventReader::is_empty()
will return true
.
For usage, see EventReader::is_empty()
.
Trait Implementations§
Source§impl<E: Event> SystemParam for EventReader<'_, '_, E>
impl<E: Event> SystemParam for EventReader<'_, '_, E>
Source§type Item<'w, 's> = EventReader<'w, 's, E>
type Item<'w, 's> = EventReader<'w, 's, E>
Self
, instantiated with new lifetimes. Read moreSource§fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State
fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State
World
access used by this SystemParam
and creates a new instance of this param’s State
.Source§unsafe fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta,
)
unsafe fn new_archetype( state: &mut Self::State, archetype: &Archetype, system_meta: &mut SystemMeta, )
Archetype
, registers the components accessed by this SystemParam
(if applicable).a Read moreSource§fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World)
fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World)
SystemParam
’s state.
This is used to apply Commands
during apply_deferred
.Source§fn queue(
state: &mut Self::State,
system_meta: &SystemMeta,
world: DeferredWorld<'_>,
)
fn queue( state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld<'_>, )
apply_deferred
.Source§unsafe fn get_param<'w, 's>(
state: &'s mut Self::State,
system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
change_tick: Tick,
) -> Self::Item<'w, 's>
unsafe fn get_param<'w, 's>( state: &'s mut Self::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'w>, change_tick: Tick, ) -> Self::Item<'w, 's>
SystemParamFunction
. Read more