我正在尝试实现透明导航栏，在滚动表视图时逐渐变为纯色 . 为此，我将导航栏设置为透明并在其后面放置一个uiview（此UIView也将覆盖状态栏） . 然后我可以在此视图上为alpha设置动画 . 但是，如果我按下一个新的视图控制器然后尝试向后滑动过渡动画似乎很奇怪 . 右上角有一个黑色方块，如此（点击图片查看动画！）：

enter image description here

代码是这样的：

override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
        navigationController?.navigationBar.shadowImage = UIImage()
        navigationController?.navigationBar.isTranslucent = true
}


override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(true)
        if !navCoverViewSet {
            guard let navBarHeight = navBarHeight() else { return }
            navCoverView.backgroundColor = UIColor.blue.withAlphaComponent(0.4)
            navCoverView.translatesAutoresizingMaskIntoConstraints = false
            navCoverView.heightAnchor.constraint(equalToConstant: navBarHeight).isActive = true
            navCoverView.widthAnchor.constraint(equalToConstant: view.frame.size.width).isActive =  true
            navCoverView.bottomAnchor.constraint(equalTo: view.topAnchor, constant: 0)
            view.addSubview(navCoverView)
            navCoverViewSet = true
        }
    }

    func navBarHeight() -> CGFloat? {
        guard let navBarHeight: CGFloat = navigationController?.navigationBar.frame.size.height else { return nil }
        let statusBarSize: CGSize = UIApplication.shared.statusBarFrame.size
        let statusBarHeight: CGFloat = min(statusBarSize.width, statusBarSize.height)
        return navBarHeight + statusBarHeight
}

任何想法为什么会这样？我会喜欢这方面的建议 . 谢谢！

ios swift uinavigationcontroller uinavigationbar