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).

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impl<'w, 's, E> EventReader<'w, 's, E>
where E: Event,

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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.

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

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

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pub fn len(&self) -> usize

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

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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
    }
}
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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§

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

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

Formats the value using the given formatter. Read more
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impl<E> SystemParam for EventReader<'_, '_, E>
where E: Event,

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type State = FetchState<E>

Used to store data which persists across invocations of a system.
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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
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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.
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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).
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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.
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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
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impl<'w, 's, E> ReadOnlySystemParam for EventReader<'w, 's, E>

Auto Trait Implementations§

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

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

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

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

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

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

Blanket Implementations§

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

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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

Mutably borrows from an owned value. Read more
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impl<T> Downcast for T
where T: Any,

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

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

Convert Arc<Trait> (where Trait: Downcast) to Arc<Any>. Arc<Any> can then be further downcast into Arc<ConcreteType> where ConcreteType implements Trait.
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> Instrument for T

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

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

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

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

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<T> WithSubscriber for T

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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
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fn with_current_subscriber(self) -> WithDispatch<Self>

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