How to insert resources?

[cacilhas]

I’m not sure whether it’s something I’m doing wrong or an actual bug.

I have the following system:

impl NanpurePlugin {

    fn setup(
        mut commands: Commands,
        assets: Res<AssetServer>,
    ) -> Result {
        let easy_mode: EasyMode = false.into();
        commands.insert_resource(ClearColor(BACKGROUND_COLOR));
        commands.insert_resource(easy_mode);
        commands.insert_resource(TitleFont::new(&assets)?);
        Ok(())
    }
}

And another system that uses that TitleFont resource:

impl MainMenu {

    pub fn spawn(
        mut commands: Commands,
        font: Res<TitleFont>,
    ) {
        commands
            .spawn(Self)
            .insert(Text::new(TITLE))
            .insert(TextFont {
                font: (**font).clone(),
                font_size: 120.0,
                ..default()
            })
            .insert(TextLayout::new_with_justify(JustifyText::Center))
            .insert(TextColor(TITLE_COLOR))
            .insert(Node {
                position_type: PositionType::Relative,
                justify_self: JustifySelf::Center,
                ..default()
            })
        ;
    }

    ...
}

Then I added the first system in the Main schedule and the second one in the OnEnter(GameState::MainMenu):

impl Plugin for NanpurePlugin {

    fn build(&self, app: &mut App) {
        app
            .add_systems(Main, Self::setup)
            .init_state::<GameState>()

            // Main menu
            .add_systems(OnEnter(GameState::MainMenu), MainMenu::spawn)
            .add_systems(OnExit(GameState::MainMenu), MainMenu::despawn)
        ;
    }
}

But I’m getting the following error:

thread 'main' panicked at ~/.cargo/git/checkouts/bevy-50d7e162b728c6c6/f7c27b5/crates/bevy_ecs/src/system/function_system.rs:216:28:
nanpure::main_menu::MainMenu::spawn could not access system parameter Res<TitleFont>

Shouldn’t Res<TitleFont> exist since Main performs before OnEnter(GameState::MainMenu)?

What am I doing wrong?

[NiklasEi]

You probably want to add setup to Startup, not to Main. Take a look at https://bevy-cheatbook.github.io/programming/schedules.html#the-main-schedule.

[cacilhas]

I had tried that before using Main, with the same outcome.

I changed from Startup to Main to see whether loading the resource earlier would make it available, unsuccessfully.

[NiklasEi]

I am guessing that the MainMenu state is the initial state? That case I can reproduce. It seems that the first run of the OnEnter schedule happens before Startup/Main. That kind of makes sense to have the correct state already available during the first run of the Main schedule.
I would consider moving the setup into some "Setup" state before MainMenu.

This works for me (instead of in Startup, you could also run the setup in OnEnter of Setup state now):

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .init_state::<MyStates>()
        .add_systems(Startup, setup)
        .add_systems(OnEnter(MyStates::Next), expect)
        .run();
}

fn setup(mut commands: Commands, mut state: ResMut<NextState<MyStates>>) {
    info!("ran");
    commands.insert_resource(Test);
    state.set(MyStates::Next);
}

fn expect(test: Res<Test>) {
    info!("works");
}

#[derive(Resource)]
struct Test;

#[derive(Clone, Eq, PartialEq, Debug, Hash, Default, States)]
enum MyStates {
    #[default]
    Setup,
    Next,
}

[cacilhas]

I see.

I finally made it work, but I cannot explain how. 😬

I had the following NanpurePlugin::build method:

    fn build(&self, app: &mut App) {
        app
            .init_state::<GameState>()
            .add_systems(Startup, Self::setup)

            // Main menu
            .add_systems(OnEnter(GameState::MainMenu), MainMenu::spawn)
            .add_systems(OnExit(GameState::MainMenu), MainMenu::despawn)
        ;
    }

It wasn’t working… missing Res<TitleFont>. Then I change it to:

    fn build(&self, app: &mut App) {
        app
            .init_state::<GameState>()
            .add_systems(Startup, Self::setup)
            .add_systems(PostStartup, MainMenu::spawn)

            // Main menu
            //.add_systems(OnEnter(GameState::MainMenu), MainMenu::spawn)
            .add_systems(OnExit(GameState::MainMenu), MainMenu::despawn)
        ;
    }

And then it started working.

After that test, I reverted the changes back to the previous code and… it’s still working!

I tried to cargo clean so I could check whether it was cache or not, and it’s still working though.

Aftermath I just can’t tell what was going on. 🤷

Anyway, thanks for the help, @NiklasEi! I’m closing this issue, I guess there’s nothing more to do with it.

[cacilhas]

I found out why!

I had created a new GameState::Loading as default, and I’m using NanpurePlugin::setup now to change to GameState::MainMenu – and I had forgot that. 😬