lol gradients in UIKit 🙃🙃🙃

LinearGradientView.swift

import UIKit

@objc(CLBLinearGradientView)
class LinearGradientView: UIView {
  @objc var layerBacked: Bool {
    didSet {
      switch (layerBacked, layerView) {
      case (true, .none): addLayerView()
      case (false, .some): removeLayerView()
      default: break
      }
    }
  }

  @objc var colors: [UIColor] {
    didSet {
      layerView?.colors = colors
      setNeedsDisplay()
    }
  }

  @objc var locations: [CGFloat] {
    didSet {
      layerView?.locations = locations
      setNeedsDisplay()
    }
  }

  override init(frame: CGRect) {
    self.layerBacked = true
    self.colors = [.clear, .clear]
    self.locations = [0, 1]
    super.init(frame: frame)
    addLayerView()
    backgroundColor = .clear
    isOpaque = false
  }

  private var layerView: LayerBackedGradientView?

  private func addLayerView() {
    let layerView = LayerBackedGradientView()
    layerView.colors = colors
    layerView.locations = locations
    self.layerView = layerView
    addSubview(layerView)
  }

  private func removeLayerView() {
    layerView?.removeFromSuperview()
    layerView = nil
  }

  required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }

  override func layoutSubviews() {
    super.layoutSubviews()
    layerView?.frame = bounds
  }

  override func draw(_ rect: CGRect) {
    if layerBacked {
      super.draw(rect)
    } else {
      guard let context = UIGraphicsGetCurrentContext() else { return }
      let colorSpace = CGColorSpaceCreateDeviceRGB()
      let cgColors = colors.map({ $0.cgColor })
      let cfColors = cgColors as CFArray
      guard let gradient = CGGradient(colorsSpace: colorSpace, colors: cfColors, locations: locations) else { return }
      let end = CGPoint(x: 0, y: rect.maxY)
      context.drawLinearGradient(gradient, start: .zero, end: end, options: [])
    }
  }
}

fileprivate class LayerBackedGradientView: UIView {
  var colors: [UIColor] {
    didSet {
      gradientLayer.colors = colors.map({ $0.cgColor })
    }
  }

  var locations: [CGFloat] {
    didSet {
      gradientLayer.locations = locations as [NSNumber]
    }
  }

  private var gradientLayer: CAGradientLayer! {
    return self.layer as? CAGradientLayer
  }

  override init(frame: CGRect) {
    self.colors = [.clear, .clear]
    self.locations = [0, 1]
    super.init(frame: frame)
    backgroundColor = .clear
    gradientLayer.colors = colors.map({ $0.cgColor })
    gradientLayer.locations = locations as [NSNumber]
  }

  required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }

  override class var layerClass: AnyClass {
    return CAGradientLayer.self
  }
}