Struct bevy_ecs::event::EventWriter
source · pub struct EventWriter<'w, 's, E: Event> { /* private fields */ }
Expand description
Sends events of type T
.
Usage
EventWriter
s are usually declared as a SystemParam
.
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 flushed
// at the end of the current stage.
commands.add(|w: &mut World| {
let mut events_resource = w.resource_mut::<Events<_>>();
events_resource.send(MyEvent);
});
}
Note that this is considered non-idiomatic, and should only be used when EventWriter
will not work.
Implementations§
source§impl<'w, 's, E: Event> EventWriter<'w, 's, E>
impl<'w, 's, E: Event> EventWriter<'w, 's, E>
sourcepub fn send(&mut self, event: E)
pub fn send(&mut self, event: E)
Sends an event
. EventReader
s can then read the event.
See Events
for details.
pub fn send_batch(&mut self, events: impl IntoIterator<Item = E>)
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<'w, 's, E: Event> SystemParam for EventWriter<'w, 's, E>
impl<'w, 's, E: Event> SystemParam for EventWriter<'w, 's, E>
Auto Trait Implementations§
impl<'w, 's, E> RefUnwindSafe for EventWriter<'w, 's, E>where
E: RefUnwindSafe,
impl<'w, 's, E> Send for EventWriter<'w, 's, E>
impl<'w, 's, E> Sync for EventWriter<'w, 's, E>
impl<'w, 's, E> Unpin for EventWriter<'w, 's, E>
impl<'w, 's, E> !UnwindSafe for EventWriter<'w, 's, E>
Blanket Implementations§
source§impl<T> Downcast for Twhere
T: Any,
impl<T> Downcast for Twhere
T: Any,
source§fn into_any(self: Box<T, Global>) -> Box<dyn Any + 'static, Global>
fn into_any(self: Box<T, Global>) -> Box<dyn Any + 'static, Global>
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
. Read moresource§fn into_any_rc(self: Rc<T>) -> Rc<dyn Any + 'static>
fn into_any_rc(self: Rc<T>) -> Rc<dyn Any + 'static>
Convert
Rc<Trait>
(where Trait: Downcast
) to Rc<Any>
. Rc<Any>
can then be
further downcast
into Rc<ConcreteType>
where ConcreteType
implements Trait
. Read moresource§fn as_any(&self) -> &(dyn Any + 'static)
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. Read moresource§fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)
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. Read more