navigationController의 [hidesBarsOnSwipe , hidesBarsOnTap, hidesBarsWhenKeyboardAppears, hidesBarsWhenVerticallyCompact] 알아봅시다.

StoryBoard

onSwipe, onTap, When Keyboard Appears, When Vertically Compact 4가지 옵션이 있습니다. 

programmatically

navigationController?.hidesBarsOnSwipe = true 

navigationController?.hidesBarsOnTap = true 

navigationController?.hidesBarsWhenKeyboardAppears = true 

navigationController?.hidesBarsWhenVerticallyCompact = true