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

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.
    ///
    /// Source: [John Sundell - Custom UIView backing layers](https://twitter.com/johnsundell/status/1000099872580816897)
    override class var layerClass: AnyClass {
        return CAGradientLayer.self
    }

    var colors: [UIColor] = [] {
        didSet {
            gradientLayer?.colors = colors.map({ $0.cgColor })
        }
    }

    // MARK: - Private properties

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

    // MARK: - Constructor

    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)
    }
}