Function bevy::prelude::apply_state_transition

pub fn apply_state_transition<S>(
    event: EventWriter<'_, StateTransitionEvent<S>>,
    commands: Commands<'_, '_>,
    current_state: Option<ResMut<'_, State<S>>>,
    next_state: Option<ResMut<'_, NextState<S>>>
)
where
    S: FreelyMutableState,

If a new state is queued in NextState<S>, this system:

• Takes the new state value from NextState<S> and updates State<S>.
• Sends a relevant StateTransitionEvent
• Runs the [OnExit(exited_state)] schedule, if it exists.
• Runs the OnTransition { from: exited_state, to: entered_state }, if it exists.
• Derive any dependent states through the [ComputeDependantStates::<S>] schedule, if it exists.
• Runs the [OnEnter(entered_state)] schedule, if it exists.

If the State<S> resource does not exist, it does nothing. Removing or adding states should be done at App creation or at your own risk.

For SubStates - it only applies the state if the SubState currently exists. Otherwise, it is wiped. When a SubState is re-created, it will use the result of it’s should_exist method.