Struct bevy::ecs::event::EventWriter

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

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);
}

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

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

pub fn send(&mut self, event: E)

Sends an event, which can later be read by EventReaders.

See Events for details.

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 EventReaders. This is more efficient than sending each event individually.

See Events for details.

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

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

type State = FetchState<E>

Used to store data which persists across invocations of a system.

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.

fn init_state( world: &mut World, system_meta: &mut SystemMeta ) -> <EventWriter<'_, E> as SystemParam>::State

Registers any World access used by this SystemParam and creates a new instance of this param’s State.

fn new_archetype( state: &mut <EventWriter<'_, E> as SystemParam>::State, archetype: &Archetype, system_meta: &mut SystemMeta )

For the specified Archetype, registers the components accessed by this SystemParam (if applicable).

fn apply( state: &mut <EventWriter<'_, 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.

unsafe fn get_param<'w, 's>( state: &'s mut <EventWriter<'_, E> as SystemParam>::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'w>, change_tick: Tick ) -> <EventWriter<'_, E> as SystemParam>::Item<'w, 's>

Creates a parameter to be passed into a SystemParamFunction.

impl<'w, 's, E> ReadOnlySystemParam for EventWriter<'w, E>where E: Event, ResMut<'w, Events<E>>: ReadOnlySystemParam,