GradientView.swift

import UIKit

class GradientView: UIView {

  @IBInspectable var startColor: UIColor?
  @IBInspectable var endColor: UIColor?
  @IBInspectable var horizontal: Bool = true {
    didSet {
      let horizontalStartPoint = CGPoint(x: 0, y: 0.5)
      let horizontalEndPoint = CGPoint(x: 1, y: 0.5)
      let verticalStartPoint = CGPoint(x: 0.5, y: 0)
      let verticalEndPoint = CGPoint(x: 0.5, y: 1)
      gradientLayer.startPoint = horizontal ? horizontalStartPoint : verticalStartPoint
      gradientLayer.endPoint = horizontal ? horizontalEndPoint : verticalEndPoint
    }
  }

  var colors: [UIColor] {
    set {
      gradientLayer.colors = newValue.map({ $0.CGColor })
    }
    get {
      guard let cgColors = gradientLayer.colors as? [CGColor] else {
        return []
      }
      return cgColors.map({ UIColor(CGColor: $0) })
    }
  }

  override func awakeFromNib() {
    super.awakeFromNib()

    if let start = startColor, let end = endColor {
      colors = [start, end]
    }
  }
}

extension GradientView {

  override class func layerClass() -> AnyClass {
    return CAGradientLayer.self
  }

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

}