Thanks for your answer but this is not helping.
I don't have any issue with the focus, I'm able to focus all the items of my collectionView.
But when I'm moving the focus on the Y axis I would like to have the row containing the focused item to scroll up to the top of my collectionView. => So far when I'm moving on the Y axis the the row containing the focused item always scroll in order to be vertically centered into my collection which I don't want !