96a6eee031
# Objective
If the current example is used as is, the `button_pressed` system will
run every update.
Update the example so that it is a more ready to use for people
## Solution
Rewrote most of it.
Another solution would be to just minimally fix the problems
```Rust
.add_systems(Startup, (count_entities, setup).chain())
```
and
```Rust
fn evaluate_callbacks(query: Query<(Entity, &Callback), With<Triggered>>, mut commands: Commands) {
for (entity, callback) in query.iter() {
commands.run_system(callback.0);
commands.entity(entity).remove::<Triggered>();
}
}
```
## Testing
- Did you test these changes? If so, how?
Ran the example and pressed A / B on the keyboard
---
129 lines
3.8 KiB
Rust
129 lines
3.8 KiB
Rust
//! Demonstrates the use of "one-shot systems", which run once when triggered.
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//!
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//! These can be useful to help structure your logic in a push-based fashion,
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//! reducing the overhead of running extremely rarely run systems
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//! and improving schedule flexibility.
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//!
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//! See the [`World::run_system`](World::run_system) or
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//! [`World::run_system_once`](World#method.run_system_once_with)
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//! docs for more details.
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use bevy::{
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ecs::system::{RunSystemOnce, SystemId},
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prelude::*,
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};
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fn main() {
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App::new()
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.add_plugins(DefaultPlugins)
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.add_systems(
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Startup,
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(
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setup_ui,
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setup_with_commands,
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setup_with_world.after(setup_ui), // since we run `system_b` once in world it needs to run after `setup_ui`
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),
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)
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.add_systems(Update, (trigger_system, evaluate_callbacks).chain())
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.run();
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}
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#[derive(Component)]
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struct Callback(SystemId);
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#[derive(Component)]
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struct Triggered;
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#[derive(Component)]
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struct A;
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#[derive(Component)]
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struct B;
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fn setup_with_commands(mut commands: Commands) {
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let system_id = commands.register_one_shot_system(system_a);
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commands.spawn((Callback(system_id), A));
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}
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fn setup_with_world(world: &mut World) {
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// We can run it once manually
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world.run_system_once(system_b);
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// Or with a Callback
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let system_id = world.register_system(system_b);
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world.spawn((Callback(system_id), B));
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}
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/// Tag entities that have callbacks we want to run with the `Triggered` component.
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fn trigger_system(
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mut commands: Commands,
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query_a: Query<Entity, With<A>>,
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query_b: Query<Entity, With<B>>,
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input: Res<ButtonInput<KeyCode>>,
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) {
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if input.just_pressed(KeyCode::KeyA) {
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let entity = query_a.single();
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commands.entity(entity).insert(Triggered);
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}
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if input.just_pressed(KeyCode::KeyB) {
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let entity = query_b.single();
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commands.entity(entity).insert(Triggered);
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}
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}
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/// Runs the systems associated with each `Callback` component if the entity also has a `Triggered` component.
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///
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/// This could be done in an exclusive system rather than using `Commands` if preferred.
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fn evaluate_callbacks(query: Query<(Entity, &Callback), With<Triggered>>, mut commands: Commands) {
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for (entity, callback) in query.iter() {
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commands.run_system(callback.0);
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commands.entity(entity).remove::<Triggered>();
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}
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}
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fn system_a(mut query: Query<&mut Text>) {
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let mut text = query.single_mut();
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text.sections[2].value = String::from("A");
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info!("A: One shot system registered with Commands was triggered");
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}
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fn system_b(mut query: Query<&mut Text>) {
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let mut text = query.single_mut();
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text.sections[2].value = String::from("B");
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info!("B: One shot system registered with World was triggered");
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}
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fn setup_ui(mut commands: Commands) {
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commands.spawn(Camera2dBundle::default());
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commands.spawn(
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TextBundle::from_sections([
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TextSection::new(
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"Press A or B to trigger a one-shot system\n",
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TextStyle {
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font_size: 25.0,
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..default()
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},
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),
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TextSection::new(
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"Last Triggered: ",
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TextStyle {
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font_size: 20.0,
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..default()
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},
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),
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TextSection::new(
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"-",
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TextStyle {
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font_size: 20.0,
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color: bevy::color::palettes::css::ORANGE.into(),
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..default()
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},
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),
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])
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.with_text_justify(JustifyText::Center)
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.with_style(Style {
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align_self: AlignSelf::Center,
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justify_self: JustifySelf::Center,
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..default()
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}),
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);
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}
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