Reset events metadata when drained

Required to ensure Event readers continue functioning correctly

Author: alice-i-cecile

crates/bevy_ecs/src/event.rs

@@ -218,6 +218,13 @@ impl<T: Component> Events<T> {
             BufferState::B => self.events_a.drain(..).chain(self.events_b.drain(..)),
         };
 
+        // We must reset these values to 0 as all events have been drained
+        self.a_start_event_count = 0;
+        self.b_start_event_count = 0;
+        self.event_count = 0;
+        // Reset to A for consistency with Self::default()
+        self.state = BufferState::A;
+
         event_instances.map(|instance| {
             trace!("Events::drain_with_id -> {}", instance.event_id);
             (instance.event, instance.event_id)

examples/ecs/event_consumer.rs

@@ -51,7 +51,6 @@ fn event_trigger_system(time: Res<Time>, mut my_events: EventWriter<MyEvent>) {
 }
 
 // reads events as soon as they come in
-// FIXME: stops responding after the first time events are consumed
 fn event_listener_system(mut events: EventReader<MyEvent>) {
     for _ in events.iter() {
         info!("I heard an event!");