Inform system when entity is added or removed

[chrisapril]

Hi, is it possible to inform a system when an entity ist removed or added to the system?

Im currently using artemis and i have systems which are building there own index of entites, for example to receive all entities in an spatial area. Those systems needs to update their index when an entity is added or removed.

Thx,
Christian

[dsaltares]

You can always subscribe your EntitySystem to entity events with the Engine by implementing the EntityListener interface. However, the handler will be called every time any entity enters or leaves the engine.

You can always check whether the added/deleted entity is of interest by doing:

ImmutableArray<Entity> entities = engine.getEntitiesFor(Family.getFor(...));
entities.contains(entity);

Would that be enough?

The EntitySystem class doesn't have an associated family. We could, maybe, add listeners to the engine on a per family basis.

[chrisapril]

Hi,

that wouldnt be enough. Another problem is that when the listener gets informed, i dont have access to the component anymore (when i have understood the ashley code right).

For example i am doing something like this very often:

BehaviourSystem .....

    @Override
    protected void removed(Entity e) {
        super.removed(e);

        Behaviour b = e.getComponent(BehaviourComponent.class).getBehaviour();
        Task task = b.getCurrentTask();
        if(task != null){
            task.removeApplicant(e);
        }
    }

or i a SteeringForceSystem:

@Override
    protected void removed(Entity e) {
        super.removed(e);

        if (spatialMapper.has(e)) {
            Spatial spatial = spatialMapper.get(e);
            spatial.vel.x = 0;
            spatial.vel.y = 0;
        }

        if (steeringForceMapper.has(e)) {
            SteeringForce sf = steeringForceMapper.get(e);
            sf.steeringForce.set(0, 0);
        }
    }

[dsaltares]

Added in f90d129