How can I apply CAGradientLayer to a UINavigationController background - ios

Question

I have a UINavigationController with prefersLargeTitles = true I'd like to apply a background colour to my nav bar, with a gradient mask so the colour essentially fades to a darker version.
I have tried to create a UIView apply the mask and render this. This however involves rendering the UIView as a UIImage and then as a UIColor so I can set the barTintColor.
This works when just rendering a UIView but when setting it on the navigation bar, the behaviour is not as I would like.
I would like that gradient to fill the entire green area.
class BaseViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
configureNavigationBar()
}
override var preferredStatusBarStyle: UIStatusBarStyle {
return .lightContent
}
func hideNavigationBar() {
navigationController?.setNavigationBarHidden(true, animated: false)
}
func showNavigationBar() {
navigationController?.setNavigationBarHidden(false, animated: false)
}
private func configureNavigationBar() {
navigationController?.navigationBar.prefersLargeTitles = true
navigationController?.navigationBar.isTranslucent = false
navigationItem.title = "Home"
let v = BrandedHeader(frame: .zero)
v.frame = navigationController?.navigationBar.frame ?? .zero
navigationController?.navigationBar.barTintColor = UIColor(patternImage: v.asImage()!)
}
}
extension UIImage {
static func usingHex(_ hex: String) -> UIImage {
let color = UIColor.usingHex(hex)
let rect = CGRect(x: 0, y: 0, width: 1, height: 1)
UIGraphicsBeginImageContext(rect.size)
let context = UIGraphicsGetCurrentContext()
context!.setFillColor(color.cgColor)
context!.fill(rect)
let img = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return img!
}
}
extension UIView {
func asImage() -> UIImage? {
if #available(iOS 10.0, *) {
let renderer = UIGraphicsImageRenderer(bounds: bounds)
return renderer.image { rendererContext in
layer.render(in: rendererContext.cgContext)
}
} else {
UIGraphicsBeginImageContextWithOptions(self.bounds.size, self.isOpaque, 0.0)
defer { UIGraphicsEndImageContext() }
guard let currentContext = UIGraphicsGetCurrentContext() else {
return nil
}
self.layer.render(in: currentContext)
return UIGraphicsGetImageFromCurrentImageContext()
}
}
}
class BrandedHeader: UIView {
let gradient: CAGradientLayer = CAGradientLayer()
override init (frame: CGRect) {
super.init(frame: frame)
backgroundColor = UIColor.green
gradient.frame = frame
gradient.colors = [UIColor.clear, UIColor.black.withAlphaComponent(0.3)].map { $0.cgColor }
gradient.locations = [0.0, 0.7]
gradient.startPoint = CGPoint(x: 0.0, y: 0.0)
gradient.endPoint = CGPoint(x: 1.0, y: 0.0)
layer.insertSublayer(gradient, at: 0)
}
required init?(coder aDecoder: NSCoder) {
return nil
}
override func layoutSubviews() {
super.layoutSubviews()
gradient.frame = frame
gradient.removeAllAnimations()
}
}

Answer 1

To answer your question, I don't think gradient.frame = frame in your BrandedHeader init is doing anything. I believe you explicitly need to set the height prop in layoutSubviews.
Something like gradient.frame = CGRect(x: 0, y: 0, width: frame.width, height: 500) - although I haven't tried that so please consider adjusting the values
I'm not sure if this approach is the best approach for what you are trying to achieve, I will comeback and update this answer once I have tried another way to achieve this.

Answer 2

The following code shows how to make a navigation bar with gradient colors. It's tested under Swift 5.
// ViewController.swift //
import UIKit
class ViewController: UIViewController {
// MARK: - Variables
// MARK: - IBOutlet
// MARK: - IBAction
// MARK: - Life cycle
override func viewDidLoad() {
super.viewDidLoad()
let titleString = "Home"
let navBar = navigationController!.navigationBar
let atext = NSMutableAttributedString(string: titleString)
let range = NSMakeRange(0, titleString.count)
atext.addAttributes([NSAttributedString.Key.foregroundColor: UIColor.white], range: range)
atext.addAttributes([NSAttributedString.Key.strokeColor: UIColor.yellow], range: range)
atext.addAttributes([NSAttributedString.Key.strokeWidth: NSNumber.init(value: -1.0)], range: range)
let titleLabel: UILabel = UILabel.init(frame: CGRect(x: 50, y: 3, width: 220-100, height: 44))
titleLabel.attributedText = atext
titleLabel.textAlignment = NSTextAlignment.center
titleLabel.font = UIFont(name: "Helvetica", size: 24.0)
self.navigationItem.titleView = titleLabel
let rect = CGRect(x: 0, y: -20, width: (self.navigationController?.navigationBar.bounds.width)!, height: (self.navigationController?.navigationBar.bounds.height)! + 20)
let colors = [UIColor.blue, UIColor.purple, UIColor.red]
let points: [CGFloat] = [0.1, 0.5, 0.9]
let gradientView = GradientView(frame: rect, backColor: UIColor.white, gradientColors: colors, points: points, isVertical: true)
gradientView.backgroundColor = UIColor.white
navBar.insertSubview(gradientView, at: 1)
navBar.layer.shadowColor = UIColor.black.cgColor
navBar.layer.shadowRadius = 4.0
navBar.layer.shadowOpacity = 0.6
navBar.layer.shadowOffset = CGSize(width: 0.0, height: 2.0)
}
}
// GradientView.swift (subclass of UIView) //
import UIKit
class GradientView: UIView {
var backColor: UIColor
var gradientColors: [UIColor]
var points: [CGFloat]
var isVertical: Bool
init(frame: CGRect, backColor: UIColor, gradientColors: [UIColor], points: [CGFloat], isVertical: Bool) {
self.backColor = backColor
self.gradientColors = gradientColors
self.points = points
self.isVertical = isVertical
super.init(frame: frame)
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func draw(_ rect: CGRect) {
super.draw(rect)
backColor.set()
UIRectFill(rect)
let gradient: CAGradientLayer = CAGradientLayer()
gradient.frame = self.bounds
var colors = [CGColor]()
for i in 0..<gradientColors.count {
let color = gradientColors[i]
colors.append(color.cgColor)
}
gradient.colors = colors
var locations = [CGFloat]()
for i in 0..<points.count {
let point = points[i]
locations.append(point)
}
gradient.locations = locations as [NSNumber]
if !isVertical {
gradient.startPoint = CGPoint(x: 0.0, y: 0.0)
gradient.endPoint = CGPoint(x: 1.0, y: 0.0)
}
layer.addSublayer(gradient)
}
}
If you want to run the colors horizontally (left to right), set the isVertical switch to false.