Ordering against an `OnEnter` system not working as expected | Bevy | Page 1

zenith turret Jan 24, 2025, 10:12 PM

#

I have this add_systems call:

.add_systems(
    StateTransition,
    on_exit_item_screen.before(super::on_enter_root_menu),
)

where on_enter_root_menu's system is added like this:

.add_systems(OnEnter(PauseScreenState::Root), on_enter_root_menu)

and I thought that would work, since, at least as far as I can tell, the OnEnter schedules run within the StateTransition schedule. But this doesn't work. Here's an example run where I added a log to the top of each system:

2025-01-24T22:05:41.629673Z DEBUG game::map::pause_screen: on_enter_root_menu
2025-01-24T22:05:41.641341Z DEBUG game::map::pause_screen::item_screen: on_exit_item_screen

What am I not getting right here?

For the record, I'm not using OnExit with on_exit_item_screen because the enum variant in question looks like ShowItems(ItemCategory) and I haven't found a way to use those systems with a non-unit enum variant.

frail glacier Jan 24, 2025, 10:19 PM

#

i have a state that looks like this

enum Scene {
  MainMenu,
  Day(usize)
}

and i'm able to use OnEnter(Day(20)) and OnExit(Day(20)), etc

#

does ItemCategory implement Hash, Eq and Clone?

zenith turret Jan 25, 2025, 5:51 AM

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frail glacier i have a state that looks like this ```rust enum Scene { MainMenu, Day(usiz...

That's not what I need though, I need OnEnter(PauseScreenState::ShowItems(_)), as in, any inner value, not a specific inner value. But yes, Hash, Eq and Clone are implemented.

#

Which is why the system is like this, basically:

fn on_enter_item_screen(
    mut commands: Commands,
    mut events: EventReader<StateTransitionEvent<PauseScreenState>>,
) {
    for transition in events.read() {
        let Some(PauseScreenState::ShowItems(item_category)) = transition.entered else {
            continue;
        };
        // <the rest of the code, using `item_category`
    }
}

#

For whatever reason, it didn't occur to me to try this until just now, but this seems to work:

.add_systems(
    StateTransition,
    on_exit_item_screen.in_set(StateTransitionSteps::ExitSchedules),
)

I'm still incredibly confused as to why the original code didn't work though; without an explicit in_set, you'd think Bevy would be free to order the system exactly where it needs to go to be run before the other one.

frail glacier Jan 25, 2025, 10:05 AM

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You can create a substate with the source being ShowItems(_)

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Or a computed state

zenith turret Jan 25, 2025, 11:36 AM

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Oh, that's a thought. Thanks, I'll give that a shot. 😄

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The most embarrassing part is that I've already solved this problem in other parts of my code using ComputedStates before. 😳 Oh well, it doesn't hurt to regain lost knowledge. 😅 Thanks for the suggestions!

#Ordering against an `OnEnter` system not working as expected