Adding inner shadow to top of UIView

Question

I looked up but I couldn't find how I can add an inner shadow to UIView, only top (from top to bottom) for Swift. What is the best way add inner circle in Swift?

Edit: I've found some questions & answers on SO however they are either in obj-c or looks so complicated. I was just looking for a more Swifty way, if there is any

What I want to achieve:

Answer 1

Here's a pure Swift version that I whipped up:

public class EdgeShadowLayer: CAGradientLayer {

    public enum Edge {
        case Top
        case Left
        case Bottom
        case Right
    }

    public init(forView view: UIView,
                edge: Edge = Edge.Top,
                shadowRadius radius: CGFloat = 20.0,
                toColor: UIColor = UIColor.white,
                fromColor: UIColor = UIColor.black) {
        super.init()
        self.colors = [fromColor.cgColor, toColor.cgColor]
        self.shadowRadius = radius

        let viewFrame = view.frame

        switch edge {
            case .Top:
                startPoint = CGPoint(x: 0.5, y: 0.0)
                endPoint = CGPoint(x: 0.5, y: 1.0)
                self.frame = CGRect(x: 0.0, y: 0.0, width: viewFrame.width, height: shadowRadius)
            case .Bottom:
                startPoint = CGPoint(x: 0.5, y: 1.0)
                endPoint = CGPoint(x: 0.5, y: 0.0)
                self.frame = CGRect(x: 0.0, y: viewFrame.height - shadowRadius, width: viewFrame.width, height: shadowRadius)
            case .Left:
                startPoint = CGPoint(x: 0.0, y: 0.5)
                endPoint = CGPoint(x: 1.0, y: 0.5)
                self.frame = CGRect(x: 0.0, y: 0.0, width: shadowRadius, height: viewFrame.height)
            case .Right:
                startPoint = CGPoint(x: 1.0, y: 0.5)
                endPoint = CGPoint(x: 0.0, y: 0.5)
                self.frame = CGRect(x: viewFrame.width - shadowRadius, y: 0.0, width: shadowRadius, height: viewFrame.height)
        }
    }

    required public init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }   
}

To use it,

let topShadow = EdgeShadowLayer(forView: targetView, edge: .Top)
targetView.layer.addSublayer(topShadow)

Note that it defaults to a black-to-white gradient that's 20 points deep.

The full code, with a sample UIViewController that lets you toggle shadows on all four corners of a view, can be found at https://github.com/jrtibbetts/Tenebrae. I've also documented the EdgeShadowLayer pretty thoroughly.