Nested custom UIScrollViews animations

Question

I would like to understand how to achieve the following kind of animations in nested scroll views. You can see these animations in the iOS Weather app. Check out this video were I show you the different animations: https://dl.dropboxusercontent.com/u/615295/Weather.mov

1. Flexible header with variable alpha
2. Fixed position of the per-hour forecast, only when scrolling down
3. All these animations are smooth event when the scroll view is decelerating (the scroll velocity is respected)

Answer 1

It seems like it is implemented with UICollectionView and custom CollectionViewlayout. the Header is actually supplementary view that cant stick and the top header is showing/viewing in according to the scroll position of the collection view.