Gradient Layer not showing on UIButton - swift

Question

I am trying to create a custom UIButton that i can use throughout my application. I would like to apply a gradient as its background however the gradient is not showing up using this very simple Code.
It would be very helpful if someone could point out my mistake in the code below.
class GradientBtn: UIButton {
let gradientLayer = CAGradientLayer()
override init(frame: CGRect) {
super.init(frame: frame)
themeConfig()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
themeConfig()
}
private func themeConfig() {
//shadow
layer.shadowOffset = CGSize.zero
layer.shadowColor = UIColor.gray.cgColor
layer.shadowOpacity = 1.0
//titletext
setTitleColor(Theme.colorWhite, for: .normal)
titleLabel?.font = UIFont(name: Theme.fontAvenir, size: 18)
//rounded corners
layer.cornerRadius = frame.size.height / 2
//gradient
gradientLayer.locations = [0.0, 1.0]
gradientLayer.colors = [Theme.colorlightBlue, Theme.colorMidBlue]
gradientLayer.startPoint = CGPoint(x: 0.0, y: 0.0)
gradientLayer.endPoint = CGPoint(x: 1.0, y: 1.0)
gradientLayer.frame = bounds
layer.insertSublayer(gradientLayer, at: 0)
}
}

Answer 1

Replace
gradientLayer.colors = [Theme.colorlightBlue, Theme.colorMidBlue]
with
gradientLayer.colors = [Theme.colorlightBlue.cgColor, Theme.colorMidBlue.cgColor]
And it's always good to add
override func layoutSubviews() {
super.layoutSubviews()
gradientLayer.frame = self.bounds
}

Answer 2

Sh_Khan is right about the CGColor references, but a few additional refinements:
Rather than adding the gradient as a sublayer, make it the layerClass of the UIButton. This makes animations much better (e.g. if the button changes size on device rotation).
When you do this, remove all attempts to set the frame of the gradientLayer.
In layoutSubviews, you’ll no longer need to update the gradientLayer.frame, so remove that entirely, but you do want to put your corner rounding there.
It’s extremely unlikely to ever matter, but when you set layer.cornerRadius (or any property of the view, its layer, or that layer's sublayers), you should never refer to self.frame. The frame of the view is the CGRect in the superview’s coordinate system. Only refer to the view’s bounds within the subclass; never its frame.
Thus:
class GradientBtn: UIButton {
override class var layerClass: AnyClass { return CAGradientLayer.self }
private var gradientLayer: CAGradientLayer { return layer as! CAGradientLayer }
override init(frame: CGRect = .zero) {
super.init(frame: frame)
themeConfig()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
themeConfig()
}
private func themeConfig() {
//shadow
layer.shadowOffset = .zero
layer.shadowColor = UIColor.gray.cgColor
layer.shadowOpacity = 1
//titletext
setTitleColor(Theme.colorWhite, for: .normal)
titleLabel?.font = UIFont(name: Theme.fontAvenir, size: 18)
//gradient
gradientLayer.locations = [0, 1]
gradientLayer.colors = [Theme.colorlightBlue, Theme.colorMidBlue].map { $0.cgColor }
gradientLayer.startPoint = CGPoint(x: 0, y: 0)
gradientLayer.endPoint = CGPoint(x: 1, y: 1)
}
override func layoutSubviews() {
super.layoutSubviews()
layer.cornerRadius = min(bounds.height, bounds.width) / 2
}
}