Creator 3.8 - Collider2D can't get collision direction on BEGIN_CONTACT?

Cocos Creator
1

Hi, I’m using Creator 3.8.5 & handling 2d collision - to get direction of 2 objects when they collide
My physics engine is 'Box2D based 2D physics system"

I followed this article

and my code goes here

ballColliderComp.on(Contact2DType.BEGIN_CONTACT, (selfCollider: Collider2D, otherCollider: Collider2D, contact: IPhysics2DContact | null) => {
              const normal = contact.getWorldManifold().normal;
              log(`normal = `, normal);
              const points = contact.getWorldManifold().points;
              log(`points = `, points);
 });

But normal always return null & points always return an empty array []

Could anyone please tell me if I did something wrong?
Thanks!

image

2

I have just found the problem why normal & points were all empty
My 2 colldiers of 2 objects both have “sensor” checked, it looks like for sensor colliders, no normal or points in worldManifold is calculated!