Struct bevy_ecs::event::EventWriter
source · pub struct EventWriter<'w, E: Event> { /* private fields */ }
Expand description
Sends events of type T
.
§Usage
EventWriter
s 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 Observer
s 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§
source§impl<'w, E: Event> EventWriter<'w, E>
impl<'w, E: Event> EventWriter<'w, E>
sourcepub fn send(&mut self, event: E) -> EventId<E>
pub fn send(&mut self, event: E) -> EventId<E>
Sends an event
, which can later be read by EventReader
s.
This method returns the ID of the sent event
.
See Events
for details.
sourcepub fn send_batch(
&mut self,
events: impl IntoIterator<Item = E>
) -> SendBatchIds<E> ⓘ
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 EventReader
s.
This is more efficient than sending each event individually.
This method returns the IDs of the sent events
.
See Events
for details.
Trait Implementations§
source§impl<E: Event> SystemParam for EventWriter<'_, E>
impl<E: Event> SystemParam for EventWriter<'_, E>
§type Item<'w, 's> = EventWriter<'w, E>
type Item<'w, 's> = EventWriter<'w, 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 moreimpl<'w, 's, E: Event> ReadOnlySystemParam for EventWriter<'w, E>
Auto Trait Implementations§
impl<'w, E> Freeze for EventWriter<'w, E>
impl<'w, E> RefUnwindSafe for EventWriter<'w, E>where
E: RefUnwindSafe,
impl<'w, E> Send for EventWriter<'w, E>
impl<'w, E> Sync for EventWriter<'w, E>
impl<'w, E> Unpin for EventWriter<'w, E>
impl<'w, E> !UnwindSafe for EventWriter<'w, E>
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
source§impl<T> Downcast for Twhere
T: Any,
impl<T> Downcast for Twhere
T: Any,
source§fn into_any(self: Box<T>) -> Box<dyn Any>
fn into_any(self: Box<T>) -> Box<dyn Any>
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>
fn into_any_rc(self: Rc<T>) -> Rc<dyn Any>
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)
fn as_any(&self) -> &(dyn Any + 'static)
&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)
fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)
&mut Trait
(where Trait: Downcast
) to &Any
. This is needed since Rust cannot
generate &mut Any
’s vtable from &mut Trait
’s.