Trait DetectChanges

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pub trait DetectChanges {
    // Required methods
    fn is_added(&self) -> bool;
    fn is_changed(&self) -> bool;
    fn is_added_after(&self, other: Tick) -> bool;
    fn is_changed_after(&self, other: Tick) -> bool;
    fn last_changed(&self) -> Tick;
    fn added(&self) -> Tick;
    fn changed_by(&self) -> MaybeLocation;
}

Expand description

Types that can read change detection information. This change detection is controlled by DetectChangesMut types such as ResMut.

§Example

Using types that implement DetectChanges, such as Res, provide a way to query if a value has been mutated in another system.

use bevy_ecs::prelude::*;

#[derive(Resource)]
struct MyResource(u32);

fn my_system(mut resource: Res<MyResource>) {
    if resource.is_changed() {
        println!("My component was mutated!");
    }
}

Required Methods§

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fn is_added(&self) -> bool

Returns true if this value was added after the system last ran.

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fn is_changed(&self) -> bool

Returns true if this value was added or mutably dereferenced either since the last time the system ran or, if the system never ran, since the beginning of the program.

To check if the value was mutably dereferenced only, use this.is_changed() && !this.is_added().

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fn is_added_after(&self, other: Tick) -> bool

Returns true if this value was added after the other tick.

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fn is_changed_after(&self, other: Tick) -> bool

Returns true if this value was added or mutably dereferenced after the other tick.

§Example

fn system(query: Query<(Ref<Source>, &mut Target)>) {
    for (source, mut target) in query {
        // Only convert the source to the target if the source is newer
        if source.is_changed_after(target.last_changed()) {
            *target = Target::from_source(&source);
        }
    }
}

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