ddf466603c
# Objective The removal detection example shows an outdated pattern. ## Solution Show how to do this with observers.
61 lines
2.3 KiB
Rust
61 lines
2.3 KiB
Rust
//! This example shows how you can know when a [`Component`] has been removed, so you can react to it.
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//!
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//! When a [`Component`] is removed from an [`Entity`], all [`Observer`] with an [`OnRemove`] trigger for
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//! that [`Component`] will be notified. These observers will be called immediately after the
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//! [`Component`] is removed. For more info on observers, see the
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//! [observers example](https://github.com/bevyengine/bevy/blob/main/examples/ecs/observers.rs).
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//!
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//! Advanced users may also consider using a lifecycle hook
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//! instead of an observer, as it incurs less overhead for a case like this.
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//! See the [component hooks example](https://github.com/bevyengine/bevy/blob/main/examples/ecs/component_hooks.rs).
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use bevy::prelude::*;
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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(Startup, setup)
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// This system will remove a component after two seconds.
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.add_systems(Update, remove_component)
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// This observer will react to the removal of the component.
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.observe(react_on_removal)
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.run();
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}
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/// This `struct` is just used for convenience in this example. This is the [`Component`] we'll be
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/// giving to the `Entity` so we have a [`Component`] to remove in `remove_component()`.
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#[derive(Component)]
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struct MyComponent;
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fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
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commands.spawn(Camera2dBundle::default());
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commands.spawn((
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SpriteBundle {
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texture: asset_server.load("branding/icon.png"),
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..default()
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},
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// Add the `Component`.
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MyComponent,
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));
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}
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fn remove_component(
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time: Res<Time>,
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mut commands: Commands,
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query: Query<Entity, With<MyComponent>>,
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) {
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// After two seconds have passed the `Component` is removed.
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if time.elapsed_seconds() > 2.0 {
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if let Some(entity) = query.iter().next() {
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commands.entity(entity).remove::<MyComponent>();
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}
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}
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}
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fn react_on_removal(trigger: Trigger<OnRemove, MyComponent>, mut query: Query<&mut Sprite>) {
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// The `OnRemove` trigger was automatically called on the `Entity` that had its `MyComponent` removed.
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let entity = trigger.entity();
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if let Ok(mut sprite) = query.get_mut(entity) {
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sprite.color = Color::srgb(0.5, 1., 1.);
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}
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}
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