pub struct EventReader<'w, 's, E>
where 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> EventReader<'w, 's, E>
where E: Event,

source

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.

source

pub fn read_with_id(&mut self) -> EventIteratorWithId<'_, E>

Like read, except also returning the EventId of the events.

source

pub fn len(&self) -> usize

Determines the number of events available to be read from this EventReader without consuming any.

source

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
    }
}
source

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<'w, 's, E> Debug for EventReader<'w, 's, E>
where E: Debug + Event,

source§

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

Formats the value using the given formatter. Read more
source§

impl<E> SystemParam for EventReader<'_, '_, E>
where E: Event,

§

type State = FetchState<E>

Used to store data which persists across invocations of a system.
§

type Item<'w, 's> = EventReader<'w, 's, E>

The item type returned when constructing this system param. The value of this associated type should be Self, instantiated with new lifetimes. Read more
source§

fn init_state( world: &mut World, system_meta: &mut SystemMeta ) -> <EventReader<'_, '_, E> as SystemParam>::State

Registers any World access used by this SystemParam and creates a new instance of this param’s State.
source§

fn new_archetype( state: &mut <EventReader<'_, '_, E> as SystemParam>::State, archetype: &Archetype, system_meta: &mut SystemMeta )

For the specified Archetype, registers the components accessed by this SystemParam (if applicable).
source§

fn apply( state: &mut <EventReader<'_, '_, E> as SystemParam>::State, system_meta: &SystemMeta, world: &mut World )

Applies any deferred mutations stored in this SystemParam’s state. This is used to apply Commands during apply_deferred.
source§

unsafe fn get_param<'w, 's>( state: &'s mut <EventReader<'_, '_, E> as SystemParam>::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'w>, change_tick: Tick ) -> <EventReader<'_, '_, E> as SystemParam>::Item<'w, 's>

Creates a parameter to be passed into a SystemParamFunction. Read more
source§

impl<'w, 's, E> ReadOnlySystemParam for EventReader<'w, 's, E>

Auto Trait Implementations§

§

impl<'w, 's, E> RefUnwindSafe for EventReader<'w, 's, E>
where E: RefUnwindSafe,

§

impl<'w, 's, E> Send for EventReader<'w, 's, E>

§

impl<'w, 's, E> Sync for EventReader<'w, 's, E>

§

impl<'w, 's, E> Unpin for EventReader<'w, 's, E>

§

impl<'w, 's, E> !UnwindSafe for EventReader<'w, 's, E>

Blanket Implementations§

source§

impl<T> Any for T
where T: 'static + ?Sized,

source§

fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
source§

impl<T, U> AsBindGroupShaderType<U> for T
where U: ShaderType, &'a T: for<'a> Into<U>,

source§

fn as_bind_group_shader_type(&self, _images: &RenderAssets<Image>) -> U

Return the T ShaderType for self. When used in AsBindGroup derives, it is safe to assume that all images in self exist.
source§

impl<T> Borrow<T> for T
where T: ?Sized,

source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

impl<T> BorrowMut<T> for T
where T: ?Sized,

source§

fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
source§

impl<T> Downcast<T> for T

source§

fn downcast(&self) -> &T

source§

impl<T> Downcast for T
where T: Any,

source§

fn into_any(self: Box<T>) -> Box<dyn Any>

Convert Box<dyn Trait> (where Trait: Downcast) to Box<dyn Any>. Box<dyn Any> can then be further downcast into Box<ConcreteType> where ConcreteType implements Trait.
source§

fn into_any_rc(self: Rc<T>) -> Rc<dyn Any>

Convert Rc<Trait> (where Trait: Downcast) to Rc<Any>. Rc<Any> can then be further downcast into Rc<ConcreteType> where ConcreteType implements Trait.
source§

fn as_any(&self) -> &(dyn Any + 'static)

Convert &Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &Any’s vtable from &Trait’s.
source§

fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)

Convert &mut Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &mut Any’s vtable from &mut Trait’s.
source§

impl<T> DowncastSync for T
where T: Any + Send + Sync,

source§

fn into_any_arc(self: Arc<T>) -> Arc<dyn Any + Send + Sync>

Convert Arc<Trait> (where Trait: Downcast) to Arc<Any>. Arc<Any> can then be further downcast into Arc<ConcreteType> where ConcreteType implements Trait.
source§

impl<T> From<T> for T

source§

fn from(t: T) -> T

Returns the argument unchanged.

source§

impl<S> FromSample<S> for S

source§

fn from_sample_(s: S) -> S

source§

impl<T> Instrument for T

source§

fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
source§

fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
source§

impl<T, U> Into<U> for T
where U: From<T>,

source§

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

source§

impl<T, U> ToSample<U> for T
where U: FromSample<T>,

source§

fn to_sample_(self) -> U

source§

impl<T, U> TryFrom<U> for T
where U: Into<T>,

§

type Error = Infallible

The type returned in the event of a conversion error.
source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
source§

impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

§

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
source§

impl<T> Upcast<T> for T

source§

fn upcast(&self) -> Option<&T>

source§

impl<T> WithSubscriber for T

source§

fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
source§

fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more
source§

impl<S, T> Duplex<S> for T
where T: FromSample<S> + ToSample<S>,

source§

impl<T> Settings for T
where T: 'static + Send + Sync,

source§

impl<T> WasmNotSend for T
where T: Send,

source§

impl<T> WasmNotSendSync for T

source§

impl<T> WasmNotSync for T
where T: Sync,