self sizing cell

FlowLayout

flowLayout.estimatedItemSize = UICollectionViewFlowLayoutAutomaticSize

collectionViewCell

class CollectionViewCell: UICollectionViewCell {

    @IBOutlet weak var titleLabel: UILabel! {
        didSet {
            titleLabel.text = nil
        }
    }
    @IBOutlet weak var textLabel: UILabel! {
        didSet {
            textLabel.text = nil
        }
    }
    @IBOutlet weak var separator: UIView!
    @IBOutlet weak var widthLayout: NSLayoutConstraint?

    override func awakeFromNib() {
        super.awakeFromNib()
        // 本当は CollectionView の幅とかを指定したほうが良い
        setCellWidth(UIScreen.main.bounds.width)
    }

    func setCellWidth(_ width: CGFloat) {
        widthLayout?.constant = width
    }

    class func nib() -> UINib {
        return UINib(nibName: "\(self)", bundle: nil)
    }

    override func prepareForReuse() {
        super.prepareForReuse() // Don't forget!
    }
}