ios - CAGradientLayer 不显示

Question

我已经查看了很多其他类似问题的答案，但似乎没有一个答案能解决我的问题，因此寻求一点帮助。

我正在尝试对 UIButton 应用垂直渐变，但渐变层没有显示在我的 View 中。相关代码如下:

let darkPurple = UIColor(displayP3Red: 61.0/255.0, green: 3.0/255.0, blue: 110.0/255.0, alpha: 1.0)
let lightPurple = UIColor(displayP3Red: 90.0/255.0, green: 32.0/255.0, blue: 130.0/255.0, alpha: 1.0)

let addButton = UIButton(frame: CGRect(x: 0, y: 0, width: 0, height: 0))
addButton.title = "Start counting"
addButton.layer.cornerRadius = 30.0
addButton.layer.borderWidth = 1.0
addButton.layer.borderColor = darkPurple.cgColor
addButton.translatesAutoresizingMaskIntoConstraints = false
myView.addSubview(addButton)
addButton.applyGradient(with: [lightPurple, darkPurple], gradientOrientation: .vertical)

...以及应用渐变的代码:

typealias GradientPoints = (startPoint: CGPoint, endPoint: CGPoint)

enum GradientOrientation {
  case topRightBottomLeft
  case topLeftBottomRight
  case horizontal
  case vertical

  var startPoint: CGPoint {
    return points.startPoint
  }

  var endPoint: CGPoint {
    return points.endPoint
  }

  var points: GradientPoints {
    switch self {
    case .topRightBottomLeft:
      return (CGPoint(x: 0.0, y: 1.0), CGPoint(x: 1.0, y: 0.0))
    case .topLeftBottomRight:
      return (CGPoint(x: 0.0, y: 0.0), CGPoint(x: 1.0, y: 1.0))
    case .horizontal:
      return (CGPoint(x: 0.0, y: 0.0), CGPoint(x: 1.0, y: 0.0))
    case .vertical:
      return (CGPoint(x: 0.0, y: 0.0), CGPoint(x: 0.0, y: 1.0))
    }
  }
}

extension UIView {
  func applyGradient(with colors: [UIColor], gradientOrientation orientation: GradientOrientation) {
    let gradient = CAGradientLayer()
    gradient.frame = self.bounds
    gradient.colors = colors.map { $0.cgColor }
    gradient.startPoint = orientation.startPoint
    gradient.endPoint = orientation.endPoint
    gradient.borderColor = self.layer.borderColor
    gradient.borderWidth = self.layer.borderWidth
    gradient.cornerRadius = self.layer.cornerRadius
    gradient.masksToBounds = true
    gradient.isHidden = false

    self.layer.insertSublayer(gradient, at: 0)
  }
}

这是我得到的: empty button

感谢您的帮助!

Answer 1

对于已经花费数小时搜索的人(就像我一样):

请确保您的颜色数组包含 CGColor 而不是 UIColor，根据文档:

colors

An array of CGColorRef objects defining the color of eachgradient stop. Animatable.

https://developer.apple.com/documentation/quartzcore/cagradientlayer/1462403-colors

奖励:这个小代码片段会导致应用程序崩溃，如果您再次错过它(推荐使用#if DEBUG)

extension CAGradientLayer {
    dynamic var colors: [Any]? {
        get { self.value(forKey: "colors") as? [Any] }
        set {
            if let newValue = newValue {
                for color in newValue {
                    if color is UIColor {
                        fatalError("CAGradientLayer.colors must contain only CGColor! UIColor was found")
                    }
                }
            }
            super.setValue(newValue, forKey: "colors")
        }
    }
}