A Simple UIView Wrapper for CAGradientLayer

GradientView.swift

/// A Simple UIView Wrapper for CAGradientLayer. It is a plain UIView whose layer
/// is a CAGradientLayer. It is useful if using a view is more convenient than using a layer, e.g.
/// because you want to use autoresizing masks.
class GradientView: UIView {
    
    /// The direction to draw the gradient, in a single point coordinate space.
    enum Direction {
        
        /// Draw the gradient from top to bottom.
        case vertical
        
        /// Draw the gradient from left to right.
        case horizontal
        
        // Draw the gradient in a custom direction providing the start and end points.
        case custom(start: CGPoint, end: CGPoint)
       
        /// The start point of the gradient when drawn.
        var startPoint: CGPoint {
            switch self {
            case .vertical:
                return CGPoint(x: 0.5, y: 0)
            case .horizontal:
                return CGPoint(x: 0, y: 0.5)
            case .custom(start: let start, end: _):
                return start
            }
        }
        
        /// The end point of the gradient when drawn.
        var endPoint: CGPoint {
            switch self {
            case .vertical:
                return CGPoint(x: 0.5, y: 1)
            case .horizontal:
                return CGPoint(x: 1, y: 0.5)
            case .custom(start: _, end: let end):
                return end
            }
        }
        
    }
    
    /// The CAGradientLayer instance containing the gradient information to play.
    var gradientLayer: CAGradientLayer {
        //swiftlint:disable force_cast
        return layer as! CAGradientLayer
        //swiftlint:enable force_cast
    }
    
    // Override UIView property. The class used to create the layer for instances of this class.
    override static var layerClass: AnyClass {
        return CAGradientLayer.self
    }
    
    /// An array of UIColor objects defining the color of each gradient stop. Animatable.
    ///
    /// Defaults to nil.
    var colors: [UIColor]? {
        didSet {
            gradientLayer.colors = colors?.map { $0.cgColor }
        }
    }
    
    /// An optional array of Double objects defining the location of each gradient stop. Animatable.
    ///
    /// The gradient stops are specified as values between 0 and 1. 
    /// The values must be monotonically increasing. If nil, the stops are spread uniformly across the range. 
    ///
    /// Defaults to nil.
    var locations: [Double]? {
        didSet {
            gradientLayer.locations = locations?.map(NSNumber.init(value:))
        }
    }
    
    /// The direction to draw the gradient. Animatable.
    ///
    /// Defaults to vertical:
    ///     - startPoint: (0.5, 0.0)
    ///     - endPoint:   (0.5, 1.0)
    var direction: Direction {
        didSet {
            gradientLayer.startPoint = direction.startPoint
            gradientLayer.endPoint   = direction.endPoint
        }
    }
    
    /// Initialise with default values calling didSet to update the underlying gradient layer in the process.
    override init(frame: CGRect) {
        
        self.colors    = nil
        self.direction = .vertical
        self.locations = nil
        
        super.init(frame: frame)
        
    }
    
    /// Not yet implemented.
    required init?(coder aDecoder: NSCoder) {
        fatalError("not implemented")
    }
    
}