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Trait bevy::ecs::prelude::DetectChanges

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pub trait DetectChanges {
    fn is_added(&self) -> bool;
    fn is_changed(&self) -> bool;
    fn set_changed(&mut self);
    fn last_changed(&self) -> u32;
}
Expand description

Types that implement reliable change detection.

Example

Using types that implement DetectChanges, such as ResMut, provide a way to query if a value has been mutated in another system. Normally change detecting is triggered by either DerefMut or AsMut, however it can be manually triggered via DetectChanges::set_changed.

use bevy_ecs::prelude::*;

struct MyResource(u32);

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

   resource.0 = 42; // triggers change detection via [`DerefMut`]
}

Required Methods

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

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

Flags this value as having been changed.

Mutably accessing this smart pointer will automatically flag this value as having been changed. However, mutation through interior mutability requires manual reporting.

Note: This operation cannot be undone.

Returns the change tick recording the previous time this component (or resource) was changed.

Note that components and resources are also marked as changed upon insertion.

For comparison, the previous change tick of a system can be read using the SystemChangeTick SystemParam.

Implementors