mirror of
https://github.com/bevyengine/bevy
synced 2024-11-25 22:20:20 +00:00
d85b89b430
Updates old comments from the old `stage::UPDATE` terminology to the new `CoreStage` enum.
74 lines
2.8 KiB
Rust
74 lines
2.8 KiB
Rust
// This example shows how you can know when a `Component` has been removed, so you can react to it.
|
|
|
|
use bevy::prelude::*;
|
|
|
|
fn main() {
|
|
// Information regarding removed `Component`s is discarded at the end of each frame, so you need
|
|
// to react to the removal before the frame is over.
|
|
//
|
|
// Also, `Components` are removed via a `Command`. `Command`s are applied after a stage has
|
|
// finished executing. So you need to react to the removal at some stage after the
|
|
// `Component` is removed.
|
|
//
|
|
// With these constraints in mind we make sure to place the system that removes a `Component` on
|
|
// the `CoreStage::Update' stage, and the system that reacts on the removal on the
|
|
// `CoreStage::PostUpdate` stage.
|
|
App::build()
|
|
.add_plugins(DefaultPlugins)
|
|
.add_startup_system(setup.system())
|
|
.add_system_to_stage(CoreStage::Update, remove_component.system())
|
|
.add_system_to_stage(CoreStage::PostUpdate, react_on_removal.system())
|
|
.run();
|
|
}
|
|
|
|
// This `Struct` is just used for convenience in this example. This is the `Component` we'll be
|
|
// giving to the `Entity` so we have a `Component` to remove in `remove_component()`.
|
|
struct MyComponent;
|
|
|
|
fn setup(
|
|
commands: &mut Commands,
|
|
asset_server: Res<AssetServer>,
|
|
mut materials: ResMut<Assets<ColorMaterial>>,
|
|
) {
|
|
let texture = asset_server.load("branding/icon.png");
|
|
|
|
commands
|
|
.spawn(OrthographicCameraBundle::new_2d())
|
|
.spawn(SpriteBundle {
|
|
material: materials.add(texture.into()),
|
|
..Default::default()
|
|
})
|
|
.with(MyComponent); // Add the `Component`.
|
|
}
|
|
|
|
fn remove_component(
|
|
time: Res<Time>,
|
|
commands: &mut Commands,
|
|
query: Query<Entity, With<MyComponent>>,
|
|
) {
|
|
// After two seconds have passed the `Component` is removed.
|
|
if time.seconds_since_startup() > 2.0 {
|
|
if let Some(entity) = query.iter().next() {
|
|
commands.remove_one::<MyComponent>(entity);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn react_on_removal(
|
|
mut materials: ResMut<Assets<ColorMaterial>>,
|
|
query: Query<(Entity, &Handle<ColorMaterial>)>,
|
|
) {
|
|
// Note: usually this isn't how you would handle a `Query`. In this example it makes things
|
|
// a bit easier to read.
|
|
let (query_entity, material) = query.iter().next().unwrap();
|
|
|
|
// `Query.removed<T>` returns an array with the `Entity`s in the `Query` that had its
|
|
// `Component` `T` (in this case `MyComponent`) removed at some point earlier during the frame.
|
|
for entity in query.removed::<MyComponent>() {
|
|
// We compare the `Entity` that had its `MyComponent` `Component` removed with the `Entity`
|
|
// in the current `Query`. If they match all red is removed from the material.
|
|
if query_entity == *entity {
|
|
materials.get_mut(material).unwrap().color.set_r(0.0);
|
|
}
|
|
}
|
|
}
|