Struct EventCursor

pub struct EventCursor<E: Event> { /* private fields */ }

Stores the state for an EventReader or EventMutator.

Access to the Events<E> resource is required to read any incoming events.

In almost all cases, you should just use an EventReader or EventMutator, which will automatically manage the state for you.

However, this type can be useful if you need to manually track events, such as when you’re attempting to send and receive events of the same type in the same system.

Example

use bevy_ecs::prelude::*;
use bevy_ecs::event::{Event, Events, EventCursor};

#[derive(Event, Clone, Debug)]
struct MyEvent;

/// A system that both sends and receives events using a [`Local`] [`EventCursor`].
fn send_and_receive_events(
    // The `Local` `SystemParam` stores state inside the system itself, rather than in the world.
    // `EventCursor<T>` is the internal state of `EventMutator<T>`, which tracks which events have been seen.
    mut local_event_reader: Local<EventCursor<MyEvent>>,
    // We can access the `Events` resource mutably, allowing us to both read and write its contents.
    mut events: ResMut<Events<MyEvent>>,
) {
    // We must collect the events to resend, because we can't mutate events while we're iterating over the events.
    let mut events_to_resend = Vec::new();

    for event in local_event_reader.read(&mut events) {
         events_to_resend.push(event.clone());
    }

    for event in events_to_resend {
        events.send(MyEvent);
    }
}

Implementations

impl<E: Event> EventCursor<E>

pub fn read<'a>(&'a mut self, events: &'a Events<E>) -> EventIterator<'a, E>

See EventReader::read

pub fn read_mut<'a>( &'a mut self, events: &'a mut Events<E>, ) -> EventMutIterator<'a, E>

See EventMutator::read

pub fn read_with_id<'a>( &'a mut self, events: &'a Events<E>, ) -> EventIteratorWithId<'a, E>

See EventReader::read_with_id

pub fn read_mut_with_id<'a>( &'a mut self, events: &'a mut Events<E>, ) -> EventMutIteratorWithId<'a, E>

See EventMutator::read_with_id

pub fn len(&self, events: &Events<E>) -> usize

See EventReader::len

pub fn missed_events(&self, events: &Events<E>) -> usize

Amount of events we missed.

pub fn is_empty(&self, events: &Events<E>) -> bool

See EventReader::is_empty()

pub fn clear(&mut self, events: &Events<E>)

See EventReader::clear()

Trait Implementations

impl<E: Event> Clone for EventCursor<E>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<E: Debug + Event> Debug for EventCursor<E>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<E: Event> Default for EventCursor<E>

fn default() -> Self

Returns the “default value” for a type.