Function bevy::ecs::schedule::common_conditions::state_exists
source · pub fn state_exists<S>(current_state: Option<Res<'_, State<S>>>) -> boolwhere
S: States,
Expand description
A Condition
-satisfying system that returns true
if the state machine exists.
Example
#[derive(States, Clone, Copy, Default, Eq, PartialEq, Hash, Debug)]
enum GameState {
#[default]
Playing,
Paused,
}
app.add_systems(
// `state_exists` will only return true if the
// given state exists
my_system.run_if(state_exists::<GameState>),
);
fn my_system(mut counter: ResMut<Counter>) {
counter.0 += 1;
}
// `GameState` does not yet exist `my_system` won't run
app.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 0);
world.init_resource::<State<GameState>>();
// `GameState` now exists so `my_system` will run
app.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 1);