An image view containing a vertical gradient as background.

VerticalGradientImageView.swift

//
//  VerticalGradientImageView.swift
//
//  Created by Felix Mau on 23/09/18.
//  Copyright © 2018 Felix Mau. All rights reserved.
//

import UIKit

final class VerticalGradientImageView: UIImageView {

  // MARK: - Public Properties

  /// > By overriding `layerClass` you can tell UIKit what CALayer class to use for a UIView's backing layer.
  /// > That way you can reduce the amount of layers, and don't have to do any manual layout.
  ///
  /// [John Sundell - Custom UIView backing layers](https://twitter.com/johnsundell/status/1000099872580816897)
  override class var layerClass: AnyClass {
    CAGradientLayer.self
  }

  var colors = [UIColor]() {
    didSet {
      gradientLayer?.colors = colors.map(\.cgColor)
    }
  }

  // MARK: - Private Properties

  private var gradientLayer: CAGradientLayer? {
    layer as? CAGradientLayer
  }

  // MARK: - Instance Lifecycle

  override init(frame: CGRect) {
    super.init(frame: frame)

    setUpGradientLayer()
  }

  required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)

    setUpGradientLayer()
  }

  // MARK: - Private Methods

  private func setUpGradientLayer() {
    gradientLayer?.startPoint = .zero
    gradientLayer?.endPoint = CGPoint(x: 0, y: 1)
  }
}