I would like to populate UICollectionView in reverse order so that the last item of the UICollectionView fills first and then the second last and so on. Actually I'm applying animation and items are showing up one by one. Therefore, I want the last item to show up first.
I'm assuming you are using UICollectionViewFlawLayout, and this doesn't have logic to do that, it only works in a TOP-LEFT BOTTOM-RIGHT order. To do that you have to build your own layout, which you can do creating a new object that inherits from UICollectionViewLayout.
It seems like a lot of work but is not really that much, you have to implement 4 methods, and since your layout is just bottom-up should be easy to know the frames of each cell.