Instantiate and getting properties

Unity Engine
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1

Hi,

I have a test class setup like this:

public class BoundsTest : MonoBehaviour
{
    [SerializeField] private BoxCollider2D boxCollider;
    public Bounds Bounds => boxCollider.bounds;
}

Another class is instantiating a prefab of the above. After instantiation I want to move the object, and get the updated Bounds. I realize that it may take some time for the box collider to update thus I’m waiting for a frame to get its values.

    public class BoundsChecker : MonoBehaviour
    {
        [...]
        //I'm running this as StartCoroutine(TestWithWait());
        private IEnumerator TestWithWait()
        {
            instance = Instantiate(prefab);           
            Debug.Log("Bounds center before: " + instance.Bounds.center); //Logs (0,0,0)

            instance.transform.position += new Vector3(2, 0);        
            Debug.Log("Bounds center after: " + instance.Bounds.center); //Logs (0,0,0)

            yield return null;            
            Debug.Log("Bounds center after wait: " + instance.Bounds.center); //Logs (0,0,0), sometimes (2,0,0)
        }
    }

The problem I’m facing is getting the bounds center is not consistent at all. The logged center right after the position change is the same as before moving as I expected. The problem is even though I wait for the end of the frame the bounds are sometimes still not updated. 9 times out of 10 it logs out the default value. Sometimes I get lucky and logs out the correct center.

Waiting for some seconds does the trick. By that time the bounds are updated but I obviously don’t want to wait for that long.

Is there a way to get consistent results without having to wait too long and clutter my code with hardcoded wait values?

Thanks in advance

2

According to chatgpt

This delay happens because physics updates, including collider bounds recalculations, occur during the physics update step, which happens right after the end of a frame (during the FixedUpdate phase).

yield return new WaitForFixedUpdate() does indeed solve the problem.

3

CAUTION: using the Renderer.bounds (or Collider.bounds) property is frequently confusing and/or surprising.

Remember: it is an Axis-Aligned Bounding Box (AABB)!!

1 Like
4

Thanks for the heads up. Encapsulate() seems quite handy!