In iOS 9.0.x, UICollectionView in a custom UIViewController container will get incorrect top content inset. The value does not honor status bar height and navigation bar height.
For example in the code, I set the contentInset of collectionView to be (10, 0, 10, 0). In iOS simulator or device with iOS version other than 9.0.x, the collectionView's contentInset will be (74, 0, 10, 0) when view controller willLayoutSubviews. However, in iOS 9.0.x, the contentInset will always be (10, 0, 10, 0)
This repository demostrated the issue and provided a temporary fix by manually adding the values.
Please let me know if you have a better solution for this problem.
Note: The solution only works for iOS 8.0 and later. For iOS 7.1 or earlier version, check solutions of checking system version here: http://nshipster.com/swift-system-version-checking/