Struct bevy_ecs::event::EventWriter

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pub struct EventWriter<'w, E: Event> { /* private fields */ }
Expand description

Sends events of type T.

§Usage

EventWriters are usually declared as a SystemParam.


#[derive(Event)]
pub struct MyEvent; // Custom event type.
fn my_system(mut writer: EventWriter<MyEvent>) {
    writer.send(MyEvent);
}

§Observers

“Buffered” Events, such as those sent directly in Events or sent using EventWriter, do not automatically trigger any Observers watching for that event, as each Event has different requirements regarding if it will be triggered, and if so, when it will be triggered in the schedule.

§Concurrency

EventWriter param has ResMut<Events<T>> inside. So two systems declaring EventWriter<T> params for the same event type won’t be executed concurrently.

§Untyped events

EventWriter can only send events of one specific type, which must be known at compile-time. This is not a problem most of the time, but you may find a situation where you cannot know ahead of time every kind of event you’ll need to send. In this case, you can use the “type-erased event” pattern.

fn send_untyped(mut commands: Commands) {
    // Send an event of a specific type without having to declare that
    // type as a SystemParam.
    //
    // Effectively, we're just moving the type parameter from the /type/ to the /method/,
    // which allows one to do all kinds of clever things with type erasure, such as sending
    // custom events to unknown 3rd party plugins (modding API).
    //
    // NOTE: the event won't actually be sent until commands get applied during
    // apply_deferred.
    commands.add(|w: &mut World| {
        w.send_event(MyEvent);
    });
}

Note that this is considered non-idiomatic, and should only be used when EventWriter will not work.

Implementations§

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impl<'w, E: Event> EventWriter<'w, E>

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pub fn send(&mut self, event: E) -> EventId<E>

Sends an event, which can later be read by EventReaders. This method returns the ID of the sent event.

See Events for details.

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pub fn send_batch( &mut self, events: impl IntoIterator<Item = E> ) -> SendBatchIds<E>

Sends a list of events all at once, which can later be read by EventReaders. This is more efficient than sending each event individually. This method returns the IDs of the sent events.

See Events for details.

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pub fn send_default(&mut self) -> EventId<E>
where E: Default,

Sends the default value of the event. Useful when the event is an empty struct. This method returns the ID of the sent event.

See Events for details.

Trait Implementations§

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impl<E: Event> SystemParam for EventWriter<'_, E>

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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> = EventWriter<'w, 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) -> Self::State

Registers any World access used by this SystemParam and creates a new instance of this param’s State.
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unsafe fn new_archetype( state: &mut Self::State, archetype: &Archetype, system_meta: &mut SystemMeta )

For the specified Archetype, registers the components accessed by this SystemParam (if applicable).a Read more
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fn apply(state: &mut Self::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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fn queue( state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld<'_> )

Queues any deferred mutations to be applied at the next apply_deferred.
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unsafe fn get_param<'w, 's>( state: &'s mut Self::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'w>, change_tick: Tick ) -> Self::Item<'w, 's>

Creates a parameter to be passed into a SystemParamFunction. Read more
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impl<'w, 's, E: Event> ReadOnlySystemParam for EventWriter<'w, E>

Auto Trait Implementations§

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impl<'w, E> Freeze for EventWriter<'w, E>

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impl<'w, E> RefUnwindSafe for EventWriter<'w, E>
where E: RefUnwindSafe,

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impl<'w, E> Send for EventWriter<'w, E>

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impl<'w, E> Sync for EventWriter<'w, E>

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impl<'w, E> Unpin for EventWriter<'w, E>

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impl<'w, E> !UnwindSafe for EventWriter<'w, E>

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