UI* prefix is reserved by UIKit

[lukeredpath]

Its generally considered good practice to use your own two/three letter prefix - should Apple introduce a UICollectionViewWaterfallLayout class in a future release of iOS, this will cause issues. Besides that, its generally helpful to have a unique prefix so there is no confusion around the origin of the class - using the UI prefix gives the impression that this is a native UIKit class.

[chiahsien]

Totally agree with you!
I will change the prefix.

Best wishes,
Nelson