Calculate size of uicollectionview

UICollectionView+DynamicCellSize.swift

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        guard let dummyCell: OABSubCategoryMenuCell = Bundle.main.loadNibNamed("OABSubCategoryMenuCell", owner: self, options: nil)?.first as? OABSubCategoryMenuCell else {
            return CGSize.zero
        }
        dummyCell.setContent(subCat: self.subCategories[indexPath.row], isSelected: false)
        dummyCell.setNeedsLayout()
        dummyCell.layoutIfNeeded()
        let size: CGSize = dummyCell.contentView.systemLayoutSizeFitting(UILayoutFittingCompressedSize)
        return size
    }