How do I set collection view's cell size via the auto layout

Question

Hi I\'m trying to resize the cell via the auto layout.

I want display the cell by the 3 by 3.

First Cell\'s margin left=0

Last Cell\'s m

Answer 1

Swift 3 version code based on vacawama answer:

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

        let cellsAcross: CGFloat = 3
        let spaceBetweenCells: CGFloat = 1
        let dim = (collectionView.bounds.width - (cellsAcross - 1) * spaceBetweenCells) / cellsAcross

        return CGSize(width: dim, height: dim)
    }