GradientView.swift

import UIKit

@IBDesignable public class GradientView: UIView {

    // MARK: - Internal

    @IBInspectable public var color1: UIColor = UIColor.magentaColor()
    @IBInspectable public var color2: UIColor = UIColor.cyanColor()
    @IBInspectable public var color3: UIColor = UIColor.clearColor()
    @IBInspectable public var color4: UIColor = UIColor.clearColor()
    @IBInspectable public var color5: UIColor = UIColor.clearColor()
    @IBInspectable public var color6: UIColor = UIColor.clearColor()
    @IBInspectable public var color7: UIColor = UIColor.clearColor()

    @IBInspectable var location1: CGFloat = 0.0
    @IBInspectable var location2: CGFloat = 1.0
    @IBInspectable var location3: CGFloat = 1.0
    @IBInspectable var location4: CGFloat = 1.0
    @IBInspectable var location5: CGFloat = 1.0
    @IBInspectable var location6: CGFloat = 1.0
    @IBInspectable var location7: CGFloat = 1.0

    // MARK: - Overrides

    override public init(frame: CGRect) {
        super.init(frame: frame)
        layer.addSublayer(gradientLayer)
    }

    required public init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        layer.addSublayer(gradientLayer)
    }

    override public func drawRect(rect: CGRect) {
        super.drawRect(rect)

        gradientLayer.colors = [color1.CGColor, color2.CGColor, color3.CGColor, color4.CGColor, color5.CGColor, color6.CGColor, color7.CGColor]
        gradientLayer.locations = [location1, location2, location3, location4, location5, location6, location7]
        gradientLayer.frame = frame
        gradientLayer.bounds = bounds
    }

    // MARK: - Private

    private let gradientLayer = CAGradientLayer()

    private func updatePercentForLocation(location: CGPoint) {
        location2 = min(1.0, max(0.0, location.y) / bounds.height)
        setNeedsDisplay()
    }
}

extension GradientView {

    override public func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
        super.touchesMoved(touches, withEvent: event)

        guard let location = touches.first?.locationInView(self) else { return }

        updatePercentForLocation(location)
    }

    override public func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        super.touchesBegan(touches, withEvent: event)

        guard let location = touches.first?.locationInView(self) else { return }

        updatePercentForLocation(location)
    }
}