Trait bevy::ecs::change_detection::DetectChanges
pub trait DetectChanges {
type Inner: ?Sized;
fn is_added(&self) -> bool;
fn is_changed(&self) -> bool;
fn set_changed(&mut self);
fn last_changed(&self) -> u32;
fn set_last_changed(&mut self, last_change_tick: u32);
fn bypass_change_detection(&mut self) -> &mut Self::Inner;
}
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::*;
#[derive(Resource)]
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 Associated Types§
Required Methods§
fn is_changed(&self) -> bool
fn is_changed(&self) -> bool
Returns true
if this value was added or mutably dereferenced after the system last ran.
fn set_changed(&mut self)
fn set_changed(&mut self)
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.
fn last_changed(&self) -> u32
fn last_changed(&self) -> u32
Returns the change tick recording the previous time this data 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
.
fn set_last_changed(&mut self, last_change_tick: u32)
fn set_last_changed(&mut self, last_change_tick: u32)
Manually sets the change tick recording the previous time this data was mutated.
Warning
This is a complex and error-prone operation, primarily intended for use with rollback networking strategies.
If you merely want to flag this data as changed, use set_changed
instead.
If you want to avoid triggering change detection, use bypass_change_detection
instead.
fn bypass_change_detection(&mut self) -> &mut Self::Inner
fn bypass_change_detection(&mut self) -> &mut Self::Inner
Manually bypasses change detection, allowing you to mutate the underlying value without updating the change tick.
Warning
This is a risky operation, that can have unexpected consequences on any system relying on this code. However, it can be an essential escape hatch when, for example, you are trying to synchronize representations using change detection and need to avoid infinite recursion.