Switching between Forge2D worlds: Gravity did not work

[ctbx86]

Hi guys!
I have a MainWorld which extends Forge2DWorld with a character inside. When the character moves to the door, a new Forge2dWorld will be loaded. But it is very strange that gravity did not work, the character did not fall due to gravity at all.
How to work around in this situation?

[spydon]

Hi, can you show how you are changing the world?

[spydon]

This is a simplified code I guess, since the constructor name on the second world is wrong?

[ctbx86]

Yes. I have fixed the code. My problem is: character moves between main world and level worlds. But in the example above, the gravity stops working when switching to the DungeonWorld. Ball and Box are just simple BodyComponent

[spydon]

Alright, you're getting an exception when running that right? That's what I get when trying a similar example locally at least.
As a workaround until we've solved that you can do this:

    final oldWorld = world;
    world.removeFromParent();
    oldWorld.removed.then((_) {
      game.world = dungeonWorld;
    });

[ctbx86]

Yes. '0 < _nodeCount is not true' exception was thrown. I replaced with the code above and it works. But how to save the main world state? When remove it from the parent, I think that the state was lost.

[spydon]

If you don't want to remove the state of a specific BodyComponent you have to override BodyComponent.onRemove, you could also override World.destroyBody but then make sure that the bodies that should not persist are destroyed properly.
A better way would be to save down the state that is needed when you remove the world and then re-initialize it in onMount or in onLoad if you're using a new instance.