过渡UINavigationBar颜色？

class ViewController: UIViewController, UIScrollViewDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let navigationBar = self.navigationController?.navigationBar
        navigationBar?.isTranslucent = true
        navigationBar?.backgroundColor = .clear
        navigationBar?.setBackgroundImage(UIImage(), for: .default)
        navigationBar?.shadowImage = UIImage()
    }
    
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let navigationBar = self.navigationController?.navigationBar
        let alpha = min(max(0, scrollView.contentOffset.y), 100) / 100
        let color = UIColor.black.withAlphaComponent(alpha)
        navigationBar?.titleTextAttributes = [.foregroundColor: color]
        navigationBar?.tintColor = color
    }
}