如何在swift中修复导航栏的透明度？

self.navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
self.navigationController?.navigationBar.shadowImage = UIImage()
self.navigationController?.navigationBar.isTranslucent = true

self.navigationController?.navigationBar.alpha = 0.5 // 设置透明度为0.5

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    let offsetY = scrollView.contentOffset.y
    let maxOffsetY = CGFloat(200) // 设置滚动的最大偏移量
    let alpha = offsetY / maxOffsetY
    self.navigationController?.navigationBar.alpha = alpha
}