如何在UICollectionViewCell中将UIActivityIndicatorView居中？

class CustomCollectionViewCell: UICollectionViewCell {
    let activityIndicatorView = UIActivityIndicatorView(style: .gray)
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        // 配置UIActivityIndicatorView
        activityIndicatorView.color = UIColor.black
        
        // 将UIActivityIndicatorView添加到contentView中
        contentView.addSubview(activityIndicatorView)
        
        // 使用Auto Layout布局
        activityIndicatorView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            activityIndicatorView.centerXAnchor.constraint(equalTo: contentView.centerXAnchor),
            activityIndicatorView.centerYAnchor.constraint(equalTo: contentView.centerYAnchor)
        ])
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}