如何在UINavigationBar上应用渐变颜色？

// 导航栏渐变颜色起始值
let startColor = UIColor(red: 0.0, green: 0.5, blue: 1.0, alpha: 1.0)
// 导航栏渐变颜色结束值
let endColor = UIColor(red: 0.0, green: 0.8, blue: 1.0, alpha: 1.0)

// 创建CAGradientLayer对象
let gradientLayer = CAGradientLayer()
gradientLayer.colors = [startColor.cgColor, endColor.cgColor]

// 设置渐变的起始点和结束点
gradientLayer.startPoint = CGPoint(x: 0.0, y: 0.5)
gradientLayer.endPoint = CGPoint(x: 1.0, y: 0.5)

// 设置渐变层的尺寸和位置，与导航栏一致
gradientLayer.frame = navigationController?.navigationBar.bounds ?? CGRect.zero

// 将渐变层添加到导航栏的layer中
navigationController?.navigationBar.layer.addSublayer(gradientLayer)