What is the proper way to get Components from Entities in an ITriggerEventsJob?

Questions & Answers
, ,
1

When looking through tutorials (of course older tutorials because I have not found any yet which are updated past ECS 1.0 for triggers), when using a ITriggerEventsJob and getting components from the entities in the trigger they say to use ComponentDataFromEntity. After 1.0, ComponentDataFromEntity is obsolete and Unity says to use ComponentLookup instead. The problem I have here is how to pass in ComponentLookups into the Job struct, when ComponentLookup must be marked as [ReadOnly]. Is there a different way to get Components from Entities here? Or is this the right method, but I need to do something special to give the jobs the ComponentLookups?

Here is the code that I am using:

[UpdateInGroup(typeof(FixedStepSimulationSystemGroup))]
[UpdateAfter(typeof(PhysicsSystemGroup))]
public partial class EnemyTriggerEventSystem : SystemBase
{
    //private SimulationSingleton simulationSingleton;

    protected override void OnUpdate()
    {
        var triggerJob = new TriggerJob()
        {
            meleeComponentEntities = GetComponentLookup<MeleeAttackComponent>(true),
            healthEntities = GetComponentLookup<HealthComponent>(true),
        };
        var jobHandle = triggerJob.Schedule(SystemAPI.GetSingleton<SimulationSingleton>(), Dependency);
        jobHandle.Complete();
    }

    public partial struct TriggerJob : ITriggerEventsJob
    {
        [ReadOnly] public ComponentLookup<MeleeAttackComponent> meleeComponentEntities;
        [ReadOnly] public ComponentLookup<HealthComponent> healthEntities;

        public void Execute(TriggerEvent triggerEvent)
        {
            if (meleeComponentEntities.HasComponent(triggerEvent.EntityA) && healthEntities.HasComponent(triggerEvent.EntityB))
            {
                var melee = meleeComponentEntities.GetRefRO(triggerEvent.EntityA);
                var health = healthEntities.GetRefRW(triggerEvent.EntityB);

                if (melee.ValueRO.team == health.ValueRO.team)
                    return;

                health.ValueRW.value -= melee.ValueRO.damage;
            }

            if (meleeComponentEntities.HasComponent(triggerEvent.EntityB) && healthEntities.HasComponent(triggerEvent.EntityB))
            {
                var melee = meleeComponentEntities.GetRefRO(triggerEvent.EntityB);
                var health = healthEntities.GetRefRW(triggerEvent.EntityA);

                if (melee.ValueRO.team == health.ValueRO.team)
                    return;

                health.ValueRW.value -= melee.ValueRO.damage;
            }
        }
    }
}

Here is the error if I don’t use the [ReadOnly] tag:

InvalidOperationException: The ComponentLookup
riggerJob.UserJobData.meleeComponentEntities must be marked [ReadOnly] in the job EnemyTriggerEventSystem:TriggerJob, because the container itself is marked read only.

And here is the error if I do use the [ReadOnly] tag:

InvalidOperationException: The ComponentLookup has been declared as [ReadOnly] in the job, but you are writing to it.

2

You are writing here to a

that is marked and sourced as RO. This is not allowed. Make it RW in both places and exception will go away.