UIInputViewController how to configure for custom size UIInputView

UIInputView documentation says for the property allowsSelfResizing:

When the value of this property is

false

(the default), UIKit determines an appropriate size of the input view based on its current layout. When the value of this property is

true

, UIKit honors the value returned by the

systemLayoutSizeFitting(_:)

method of the input view.

I set up a subclass of UIInputView, but the systemLayoutSizeFitting never gets called. Is anyone aware of other steps I need to take to support this feature of having a custom keyboard view height.