GroupEventType.OnEntityRemoved is also triggered when replacing a component

[jraselin]

Hi,

Below is the project configuration :

• 2 components Position and PlayerSelectActionAttack
• MonoBehaviour script AttackPointerController with 2 observers on Matcher.AllOf(Matcher.PlayerSelectActionAttack, Matcher.Position)
• MonoBehaviour script AttackController to create / destroy the entity with the 2 components
• Entitas System PlayerSelectActionAttackSystem with a group on Matcher.AllOf(Matcher.PlayerSelectActionAttack, Matcher.Position)

Position

public class PositionComponent : IComponent {
      public float x;
      public float y;
}

PlayerSelectActionAttack

public class PlayerSelectActionAttackComponent : IComponent {
}

AttackPointerController

public class AttackPointerController : MonoBehaviour {
    Vector3 position;
    GroupObserver onAdded;
    GroupObserver onRemoved;

    void Awake () {
        Pool pool = Pools.pool;
        Group group = pool.GetGroup(Matcher.AllOf(Matcher.PlayerSelectActionAttack, Matcher.Position));

        onAdded = group.CreateObserver (GroupEventType.OnEntityAdded);
        onRemoved = group.CreateObserver (GroupEventType.OnEntityRemoved);

        position = transform.position;
    }

    void Update(){
        foreach (Entity entity in onAdded.collectedEntities) {

            position.x = entity.position.x;
            position.y = entity.position.y;
            Debug.Log ("Show Attack Pointer Position To " + position);
            transform.position = position;
        }

        foreach (Entity entity in onRemoved.collectedEntities) {
            Debug.Log ("Hide Attack Pointer");
        }

    }
}

AttackController

public class AttackController : MonoBehaviour {
    Pool pool;
    Entity attackSelectedEntity;
    Toggle toggleView;


    void Awake () {
        toggleView = GetComponent<Toggle> ();
        pool = Pools.pool;      
    }

    public void onAttackCheckedValueChanged(){
        if (toggleView.isOn && attackSelectedEntity == null) {      
                attackSelectedEntity = pool.CreateEntity().IsPlayerSelectActionAttack(true).AddPosition(0,0);       
        } else if(attackSelectedEntity != null){
            Debug.Log("Destroy entity");
            pool.DestroyEntity(attackSelectedEntity);
            attackSelectedEntity = null;
        }
    }
}

PlayerSelectActionAttackSystem

public class PlayerSelectActionAttackSystem : IExecuteSystem , ISetPool {
    Group _group;

    public void SetPool(Pool pool) {
        _group = pool.GetGroup(Matcher.AllOf(Matcher.PlayerSelectActionAttack, Matcher.Position));
    }

    public void Execute() {
        foreach (Entity entity in _group.GetEntities()) {               
            Vector3 point = Camera.main.ScreenToWorldPoint (Input.mousePosition);
            entity.ReplacePosition (point.x, point.y);      
        }
    }
}

Expected behaviours

1. User clicks on Attack button, AttackController is called ONCE and creates new Entity pool.CreateEntity().IsPlayerSelectActionAttack(true).AddPosition(0,0);
2. AttackPointerController onAdded observer is updated with the created Entity and Console shows Show Attack Pointer Position To [Entity.position]
3. PlayerSelectActionAttackSystem _group field is updated with the created Entity and entity position's is replace on each frame

Console Log

AttackPointerController onRemoved.collectedEntities must be empty but the console log shows :

Show Attack Pointer Position To (-1.3, -4.3, -4.1)
Hide Attack Pointer
Show Attack Pointer Position To (-1.3, -4.3, -4.1)
Hide Attack Pointer
Show Attack Pointer Position To (-1.3, -4.3, -4.1)
Hide Attack Pointer
Show Attack Pointer Position To (-1.3, -4.3, -4.1)
Hide Attack Pointer
...

It seems like observers ignores the GroupEventType and populate onRemoved = group.CreateObserver (GroupEventType.OnEntityRemoved); with the newly created entity

Another issue

When the Entity created in AttackController is destroyed (pool.DestroyEntity(attackSelectedEntity)), there are an Exception on AttackPointerController

EntityDoesNotHaveComponentException: Cannot get component at index 11 from Entity_2()
Entity does not have a component at index 11
Entitas.Entity.GetComponent (Int32 index) (at Assets/Lib/Entitas/Entity.cs:87)
Entitas.Entity.get_position () (at Assets/Sources/Generated/PositionComponentGeneratedExtension.cs:5)
AttackPointerController.Update () (at Assets/Scripts/AttackPointerController.cs:25)

Regards

[chrischu]

The thing about groups (at least as far as I know) they do not really respond to the entity being added/removed but to each individual component.

So in your PlayerSelectActionAttackSytem you replace the position of the entity, therefore triggering all the groups again. In effect the replace triggers the remove event first (since the old position is removed) and then the add event (since the new position is added).

I hope that makes things a little bit clearer and helps you solve the problem.

[sschmid]

An entity is part of a group, when it fulfills the requirements of the matcher. In your case

Group group = pool.GetGroup(Matcher.AllOf(Matcher.PlayerSelectActionAttack, Matcher.Position));
onAdded = group.CreateObserver (GroupEventType.OnEntityAdded);
onRemoved = group.CreateObserver (GroupEventType.OnEntityRemoved);

an entity belongs to a group when it has a PlayerSelectActionAttackComponent and a PositionComponent.
Whenever you replace either of those it will be removed from the group (intentionally), because the idea is to remove the old component (=> entity doesn't match anymore) and the replace it with the new component (=> entity matches again). As a result e.ReplaceXyz will always trigger OnEntityAdded AND OnEntityRemoved

[sschmid]

Btw, AttackPointerController looks like it should be a ReactiveSystem rather than a MonoBehaviour. A ReactiveSystem is using a GroupObserver under the hood, so you don't have to mess with it. If you still want to use GroupObservers don't forget to call observer.ClearCollectedEntities()
You can get the most out of Entitas if you try putting all your logic into dedicated systems doing only one thing.

[jraselin]

Thanks for yours responses

Now, I understand the concept of ReplaceComponent

You can get the most out of Entitas if you try putting all your logic into dedicated systems doing only one thing.

Ok, I will remove all UI Logic and create dedicated systems

Regards