Swift UINavigationBar在滚动/转换时更改为意外颜色

我有一个带有透明标题栏的UIView，当用户滚动时，背景慢慢淡入白色

func imageFromColor(color: UIColor, size: CGSize) -> UIImage {
    let rect = CGRect(x: 0, y: 0, width: size.width, height: size.height)
    UIGraphicsBeginImageContext(rect.size)
    let context = UIGraphicsGetCurrentContext()

    context!.setFillColor(color.cgColor)
    context!.fill(rect)

    var image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    UIGraphicsBeginImageContext(size)
    image?.draw(in: rect)
    image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return image!
}

override func viewDidLoad() {
    super.viewDidLoad()

    // remove nav bar bottom border
    navigationController?.navigationBar.shadowImage = UIImage()

    // set nav bar button color
    let image = imageFromColor(color: UIColor(red: 255, green: 255, blue: 255, alpha: 0.0), size: CGSize(width: 1, height: 1))
    navigationController?.navigationBar.setBackgroundImage(image, for: .default)

    navigationController?.navigationBar.tintColor = .white
    navigationController?.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName: UIColor.black.withAlphaComponent(0.0)]

当用户滚动时，我会检测他们在滚动中的位置，并相应地更新导航栏

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    var alpha = (scrollView.contentOffset.y / 200)
    alpha = alpha > 1.0 ? 1.0 : alpha

    if let listName = listName, let navBar = navigationController?.navigationBar {
        let height = listName.frame.maxY - navBar.frame.maxY - 3.0
        if scrollView.contentOffset.y > 0 && scrollView.contentOffset.y >= height, !titleShowing {
            titleShowing = true

            UIView.animate(withDuration: 0.3, delay: 0, options: .curveEaseIn, animations: {
                self.titleLabel?.alpha = 1
                self.titleTopConstraint?.constant = -34.0
                self.titleLabel?.layoutIfNeeded()
            }, completion: nil)
        } else if scrollView.contentOffset.y < height, titleShowing {
            self.titleShowing = false
            self.titleLabel?.alpha = 0

            UIView.animate(withDuration: 0.4, delay: 0, options: .curveEaseIn, animations: {
                self.titleTopConstraint?.constant = 0
                self.titleLabel?.layoutIfNeeded()
            }, completion: nil)
        }
    }

    let image = imageFromColor(color: UIColor(red: 255, green: 255, blue: 255, alpha: alpha), size: CGSize(width: 1, height: 1))
    navigationController?.navigationBar.setBackgroundImage(image, for: .default)

    navigationController?.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName: UIColor.black.withAlphaComponent(alpha)]
}

正如您在下面的gif中所看到的，导航栏跳转为白色而不是清晰的，如果我返回到上一个视图控制器并向上滚动，曾经清晰的导航栏将从白色变为黑色，我无法理解这一点。我在整个VC中没有

.black

的实例

因此，要重申，有两个问题： 1） 滚动后，VC A推送至VC B，VC B的导航条跳转为白色，而不是以清晰开始 2） 滚动后，VC A推到VC B，用户返回VC A并向上滚动，导航栏从白色变为黑色，而不是从白色变为透明

我很乐意在这里帮忙

谢谢

Gif示例：

Edit:经过一些调查，似乎由于

VC A

和

VC B

都有

imageFromColor

函数，在从A转换到B之后，调用A中函数的版本，因为在转换之后技术上调用了

viewditscroll

（奇怪）。这就是为什么它会更新为白色而不是清晰

let image = imageFromColor(color: UIColor(red: 255, green: 255, blue: 255, alpha: 0.0), size: CGSize(width: 1, height: 1))
navigationController?.navigationBar.setBackgroundImage(image, for: .default)