When a child UIViewController is added within one of it’s parent’s subviews, there can be an issue where it doesn’t expand to fill it. This can often happen when we only tested on a specific device size.

The fix involves preventing the auto-resizing mask from being turned into constraints and ensuring the child view controller’s anchor constraints are all attached to the edge’s of its container view.

addChild(child)
containerView.addSubview(child.view)
child.view.translatesAutoresizingMaskIntoConstraints = false
child.view.attachAnchors(to: containerView)
child.didMove(toParent: self)

Thanks for reading and happy coding! 🙏