[artemis-odb] When does it init Systems?

Engines, Libraries and Tools
#1

hey,
I am working for the first time with artemis-odb and don´t get how/when Systems are injected into other Systems.
The Wiki says that they are at the beginning added but I get always an Nullpointer.


void create(){
      WorldConfiguration builder = new WorldConfigurationBuilder()
                .with(new CameraSystem(1920, 1080, 1), new MapSystem(), new MapRenderSystem())
                .build();

        entityEngine = new World(builder);
}
 public void render() {
        Gdx.gl.glClearColor(1, 0, 0, 1);
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
        entityEngine.setDelta(Gdx.graphics.getDeltaTime());
        entityEngine.process();
    }
public class MapRenderSystem extends BaseSystem {
public MapRenderSystem() {
        this.renderer = new OrthogonalTiledMapRenderer(mapSystem.getCurrentMap().getMap());
    }
}

public class MapSystem extends BaseSystem {
    private IGameMap currentMap;

    public MapSystem() {
        this(0);
    }
    public MapSystem(int id) { 
        changeMap(id);
    }
 public void changeMap(int id) {
        this.currentMap = MapHandler.get(id);
    }
   protected void processSystem(){}

It´s thrown from mapSystem.getCurrentMap(). mapSystem is null, although it should have been injected by artemis.

2nd)
Let´s say I want when an Character has the ChangeMapComponent to change the Map.
Means I will have to extend form BaseEntitySystem? but what then?
processSystem() is once per tick called. But changing the Map is rarely -> so more an Event. How do I get to know that an Character has that Component and then process the System? Or shall I just make an Method in mapSystem for that purpose which is called by something like MovementSystem?, But wouldn´t it be with that pretty useless to even extend from an System?