Fade a UIView in iOS using Gradient (Swift Extension)

FadeView.swift

//
// This program is free software. It comes without any warranty, to
// the extent permitted by applicable law. You can redistribute it
// and/or modify it under the terms of the Do What The Fuck You Want
// To Public License, Version 2, as published by Sam Hocevar. See
//
//              http://sam.zoy.org/wtfpl/COPYING
//
// for more details.
//

///
/// With this extension you can call .fadeView(style: ) on any view to create a fading effect.
/// Very useful when trying to fade a UIScrollView, UITableView or UICollectionView
/// This way also takes care of the "white or black" transparent gradient that happens as described here: https://stackoverflow.com/questions/24882361/ios-white-to-transparent-gradient-layer-is-gray
/// This solution is a swift implementation of the following stackoverflow question in Swift, adding more styles: https://stackoverflow.com/questions/17774761/how-to-create-a-top-fade-effect-using-uiscrollview/25408833#25408833
///
extension UIView {
	
	enum UIViewFadeStyle {
		case bottom
		case top
		case left
		case right
		
		case vertical
		case horizontal
	}
	
	func fadeView(style: UIViewFadeStyle = .bottom, percentage: Double = 0.07) {
		let gradient = CAGradientLayer()
		gradient.frame = bounds
		gradient.colors = [UIColor.white.cgColor, UIColor.clear.cgColor]
		
		let startLocation = percentage
		let endLocation = 1 - percentage
		
		switch style {
		case .bottom:
			gradient.startPoint = CGPoint(x: 0.5, y: endLocation)
			gradient.endPoint = CGPoint(x: 0.5, y: 1)
		case .top:
			gradient.startPoint = CGPoint(x: 0.5, y: startLocation)
			gradient.endPoint = CGPoint(x: 0.5, y: 0.0)
		case .vertical:
			gradient.startPoint = CGPoint(x: 0.5, y: 0.0)
			gradient.endPoint = CGPoint(x: 0.5, y: 1.0)
			gradient.colors = [UIColor.clear.cgColor, UIColor.white.cgColor, UIColor.white.cgColor, UIColor.clear.cgColor]
			gradient.locations = [0.0, startLocation, endLocation, 1.0] as [NSNumber]
			
		case .left:
			gradient.startPoint = CGPoint(x: startLocation, y: 0.5)
			gradient.endPoint = CGPoint(x: 0.0, y: 0.5)
		case .right:
			gradient.startPoint = CGPoint(x: endLocation, y: 0.5)
			gradient.endPoint = CGPoint(x: 1, y: 0.5)
		case .horizontal:
			gradient.startPoint = CGPoint(x: 0.0, y: 0.5)
			gradient.endPoint = CGPoint(x: 1.0, y: 0.5)
			gradient.colors = [UIColor.clear.cgColor, UIColor.white.cgColor, UIColor.white.cgColor, UIColor.clear.cgColor]
			gradient.locations = [0.0, startLocation, endLocation, 1.0] as [NSNumber]
		}
		
		layer.mask = gradient
	}

}