Trait DetectChanges
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§
fn is_changed(&self) -> bool
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().
fn is_added_after(&self, other: Tick) -> bool
fn is_added_after(&self, other: Tick) -> bool
Returns true if this value was added after the other tick.
fn is_changed_after(&self, other: Tick) -> bool
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);
}
}
}fn last_changed(&self) -> Tick
fn last_changed(&self) -> Tick
Returns the change tick recording the time this data was most recently 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 changed_by(&self) -> MaybeLocation
fn changed_by(&self) -> MaybeLocation
The location that last caused this to change.