How to use add_observer "On"

[cqh963852]

I'm trying out observer, but the behavior seems strange, and I'm wondering when the On Bundle property of this will work?

I checked the documentation, but it made me even more confused. https://bevy.org/news/bevy-0-17/#component-lifecycle-events

The docs says On<Add, Player> works.

but why On<GroundClick,Ground> not work?

They are both EntityEvent + Component.

My code snippet is as follows

#[derive(EntityEvent)]
struct GroundClick {
    entity: Entity,
}

fn on_click_add_point(
    mut commands: Commands,
    ground: Single<Entity, With<Ground>>,
    mouse_input: Res<ButtonInput<MouseButton>>,
) {
    if !mouse_input.just_pressed(MouseButton::Left) {
        return;
    }
    info!("test test 1");

    let entity = *ground;
    commands.trigger(GroundClick { entity });
}

impl Plugin for DrawRoadPlugin {
    fn build(&self, app: &mut App) {
        app
            .add_systems(Update, on_click_add_point)
            .add_observer(
                // won't run
                |ground_click: On<GroundClick,Ground>| {
                    info!("test test2");
                },
            )
            .add_observer(
                // can run
                |ground_click: On<GroundClick>| {
                    info!("test test3");
                },
            );
    }
}

[Zeenobit]

This is because Add uses an EntityComponentTrigger, whereas your GroundClick event uses an EntityTrigger.

You can sort of fix this by using:

#[derive(EntityEvent)]
#[entity_event(trigger = EntityComponentsTrigger<'a>)]
struct GrouncClick { ... }

To trigger it, you then need to use Commands::trigger_with, and then pass an EntityComponentsTrigger with the appropriate component ID(s).