LayoutGroup OnLayout?

Hi, just wondering if it's possible to catch an event after layout has been performed on a LayoutGroup?

seems that layout isn't calculated immediately, or I can't find a way to force a layout.

I'm adding children dynamically to a HorizontalLayoutGroup object, which is then controlled by a ScrollRect.
I need to size the group to fit the size of the children so the scroll rect can operate correctly.

Using a single frame coroutine seems to work, but wondering if there's a better way...