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);
}
Limitations
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)
pub fn send(&mut self, event: E)
Sends an event
, which can later be read by EventReader
s.
See Events
for details.
sourcepub fn send_batch(&mut self, events: impl IntoIterator<Item = E>)
pub fn send_batch(&mut self, events: impl IntoIterator<Item = 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.
See Events
for details.
sourcepub fn send_default(&mut self)where
E: Default,
pub fn send_default(&mut self)where E: Default,
Sends the default value of the event. Useful when the event is an empty struct.
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§fn new_archetype(
state: &mut Self::State,
archetype: &Archetype,
system_meta: &mut SystemMeta
)
fn new_archetype( state: &mut Self::State, archetype: &Archetype, system_meta: &mut SystemMeta )
Archetype
, registers the components accessed by this SystemParam
(if applicable).source§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§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>where ResMut<'w, Events<E>>: ReadOnlySystemParam,
Auto Trait Implementations§
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.