如何向Swift中的集合视图添加边框？

let layout = UICollectionViewFlowLayout()
collectionView.collectionViewLayout = layout

layout.sectionInset = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)

class YourViewController: UIViewController, UICollectionViewDelegateFlowLayout {
    // ...
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
        return UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
        return 10
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
        return 10
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        // 返回每个单元格的大小
        return CGSize(width: 100, height: 100)
    }
    
    // ...
}

collectionView.layer.borderWidth = 1
collectionView.layer.borderColor = UIColor.red.cgColor