Exception when adding an entity in EntityListener.entityRemoved

[wingman87]

Hi all, this time I've created a JUnit test to be more helpful:

package wingman.tests;

import org.junit.Test;

import com.badlogic.ashley.core.Component;
import com.badlogic.ashley.core.Engine;
import com.badlogic.ashley.core.Entity;
import com.badlogic.ashley.core.EntityListener;
import com.badlogic.ashley.core.Family;

public class AshleyTests {

    @Test
    public void addEntityListener_Family_Remove() {
        final Engine engine = new Engine();

        Entity e = new Entity();
        e.add(new PositionComponent());
        engine.addEntity(e);

        @SuppressWarnings("unchecked")
        Family family = Family.getFor(PositionComponent.class);
        engine.addEntityListener(family, new EntityListener() {

            public void entityRemoved(Entity entity) {
                engine.addEntity(new Entity());
            }

            public void entityAdded(Entity entity) {

            }
        });

        engine.removeEntity(e);
    }

    @Test
    public void addEntityListener_Family_Add() {
        final Engine engine = new Engine();

        Entity e = new Entity();
        e.add(new PositionComponent());

        @SuppressWarnings("unchecked")
        Family family = Family.getFor(PositionComponent.class);
        engine.addEntityListener(family, new EntityListener() {

            public void entityRemoved(Entity entity) {

            }

            public void entityAdded(Entity entity) {
                engine.addEntity(new Entity());
            }
        });

        engine.addEntity(e);
    }

    @Test
    public void addEntityListener_NoFamily_Remove() {
        final Engine engine = new Engine();

        Entity e = new Entity();
        e.add(new PositionComponent());
        engine.addEntity(e);

        @SuppressWarnings("unchecked")
        final Family family = Family.getFor(PositionComponent.class);
        engine.addEntityListener(new EntityListener() {

            public void entityRemoved(Entity entity) {
                if(family.matches(entity))
                    engine.addEntity(new Entity());
            }

            public void entityAdded(Entity entity) {

            }
        });

        engine.removeEntity(e);
    }

    @Test
    public void addEntityListener_NoFamily_Add() {
        final Engine engine = new Engine();

        Entity e = new Entity();
        e.add(new PositionComponent());

        @SuppressWarnings("unchecked")
        final Family family = Family.getFor(PositionComponent.class);
        engine.addEntityListener(new EntityListener() {

            public void entityRemoved(Entity entity) {

            }

            public void entityAdded(Entity entity) {
                if(family.matches(entity))
                    engine.addEntity(new Entity());
            }
        });

        engine.addEntity(e);
    }

    public class PositionComponent extends Component { }

}

If you run this tests, the addEntityListener_Family_Remove (and _Add) will fail with the following exception:

com.badlogic.gdx.utils.GdxRuntimeException: #iterator() cannot be used nested.
    at com.badlogic.gdx.utils.ObjectMap$Entries.hasNext(ObjectMap.java:690)
    at com.badlogic.ashley.core.Engine.removeEntityInternal(Engine.java:285)
    at com.badlogic.ashley.core.Engine.removeEntity(Engine.java:130)
    at wingman.tests.AshleyTests.addEntityListener_Family(AshleyTests.java:34)

As you can see the addEntityListener_NoFamily_Remove (and _Add) will not fail so I think the exception must be related to how the families are iterated when handling the entity removal event.

[dsaltares]

Thanks for reporting and the JUnit test. I could reproduce the issue on my end and will look into a fix.