UICollectionView with a sticky header

Simplest solution for iOS 9 + as it doesn’t need of writing subclass of UICollectionViewFlowLayout.

In viewDidLoad of viewController with collectionView use following code:

let layout = collectionView.collectionViewLayout as? UICollectionViewFlowLayout // casting is required because UICollectionViewLayout doesn't offer header pin. Its feature of UICollectionViewFlowLayout
layout?.sectionHeadersPinToVisibleBounds = true