62 lines
2.2 KiB
Rust
62 lines
2.2 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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use bevy::prelude::*;
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fn main() {
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// Information regarding removed `Component`s is discarded at the end of each frame, so you need
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// to react to the removal before the frame is over.
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//
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// Also, `Components` are removed via a `Command`, which are not applied immediately.
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// So you need to react to the removal at some stage after `apply_deferred` has run,
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// and the Component` is removed.
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//
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// With these constraints in mind we make sure to place the system that removes a `Component` in
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// `Update', and the system that reacts on the removal in `PostUpdate`.
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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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.add_systems(Update, remove_component)
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.add_systems(PostUpdate, 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(mut removed: RemovedComponents<MyComponent>, mut query: Query<&mut Sprite>) {
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// `RemovedComponents<T>::read()` returns an iterator with the `Entity`s that had their
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// `Component` `T` (in this case `MyComponent`) removed at some point earlier during the frame.
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for entity in removed.read() {
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if let Ok(mut sprite) = query.get_mut(entity) {
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sprite.color.set_r(0.0);
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}
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}
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}
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