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Added App::with_component_hooks #16977

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Added App::with_component_hooks #16977

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Objective

  • Fixes make register_component_hooks method for App #16921
  • Right now, to add component hooks, you either have to implement them in the Component trait implementation, or use app.world_mut().register_component_hooks(), which is somewhat clunky. This PR aims to introduce a more concise way to add component hooks directly from the app interface

Solution

  • I could not find a good way to implement the interface proposed in the solution directly, since the user would need to not only pass the hook itself, but also specify which hook method (on_add, on_insert, etc.) they want to add the hook to. Plus there's the issue of fallible hook add methods.
  • The proposed solution is similar to methods such as with_children on the EntityCommands, passing a closure that will mutate the target (in this case -- &mut ComponentHooks) and return the parent, allowing it to chain nicely into the multitude of calls usually associated with App.

Testing

  • I tested this by creating a new example called with_component_hooks.rs in the ecs section of examples. It works identically to the component_hooks example, but uses the new API

Showcase

Here's a snipped from the component_hooks.rs example and the comparison to the with_component_hooks.rs example

While a showcase should aim to be brief and digestible, you can use a toggleable section to save space on longer showcases:

// === component_hooks.rs ===

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, trigger_hooks)
        .init_resource::<MyComponentIndex>()
        .add_event::<MyEvent>()
        .run();
}

fn setup(world: &mut World) {
    world
        .register_component_hooks::<MyComponent>()
        .on_add(|mut world, entity, component_id| {
            let value = world.get::<MyComponent>(entity).unwrap().0;
            println!("Component: {component_id:?} added to: {entity:?} with value {value:?}");
            world
                .resource_mut::<MyComponentIndex>()
                .insert(value, entity);
            world.send_event(MyEvent);
        })
        .on_insert(|world, _, _| {
            println!("Current Index: {:?}", world.resource::<MyComponentIndex>());
        })
        .on_replace(|mut world, entity, _| {
            let value = world.get::<MyComponent>(entity).unwrap().0;
            world.resource_mut::<MyComponentIndex>().remove(&value);
        })
        .on_remove(|mut world, entity, component_id| {
            let value = world.get::<MyComponent>(entity).unwrap().0;
            println!("Component: {component_id:?} removed from: {entity:?} with value {value:?}");
            world.commands().entity(entity).despawn();
        });
}
// === with_component_hooks.rs ===

// The setup function is no longer needed in this instance
fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Update, trigger_hooks)
        .with_component_hooks::<MyComponent>(|hooks| {
            hooks
                .on_add(|mut world, entity, component_id| {
                    let value = world.get::<MyComponent>(entity).unwrap().0;
                    println!(
                        "Component: {component_id:?} added to: {entity:?} with value {value:?}"
                    );
                    world
                        .resource_mut::<MyComponentIndex>()
                        .insert(value, entity);
                    world.send_event(MyEvent);
                })
                .on_insert(|world, _, _| {
                    println!("Current Index: {:?}", world.resource::<MyComponentIndex>());
                })
                .on_replace(|mut world, entity, _| {
                    let value = world.get::<MyComponent>(entity).unwrap().0;
                    world.resource_mut::<MyComponentIndex>().remove(&value);
                })
                .on_remove(|mut world, entity, component_id| {
                    let value = world.get::<MyComponent>(entity).unwrap().0;
                    println!(
                        "Component: {component_id:?} removed from: {entity:?} with value {value:?}"
                    );
                    world.commands().entity(entity).despawn();
                });
        })
        .init_resource::<MyComponentIndex>()
        .add_event::<MyEvent>()
        .run();
}

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You added a new example but didn't add metadata for it. Please update the root Cargo.toml file.

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The generated examples/README.md is out of sync with the example metadata in Cargo.toml or the example readme template. Please run cargo run -p build-templated-pages -- update examples to update it, and commit the file change.

@alice-i-cecile alice-i-cecile added A-ECS Entities, components, systems, and events C-Usability A targeted quality-of-life change that makes Bevy easier to use S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels Dec 26, 2024
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make register_component_hooks method for App
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