How can I set the UINavigationbar with gradient co

问题:

I want to set the UINavigationbar backgroundColor to a gradient color where I would like to set it via an array of colors to create a Gradient, ideally, as accessible methods inside UINavigationBar to change its color to this gradient.

Any suggestions? (Aside from setting an image manually as the background image of the navigation bar)

回答1:

Create gradient layer and add it as background of navigation bar.

    CAGradientLayer *gradient = [CAGradientLayer layer];
    gradient.frame = self.navigationController.navigationBar.bounds;
    gradient.colors = [NSArray arrayWithObjects:(id)[[UIColor whiteColor] CGColor], (id)[[UIColor blackColor] CGColor], nil];
    [self.navigationController.navigationBar setBackgroundImage:[self imageFromLayer:gradient] forBarMetrics:UIBarMetricsDefault];

For creating image from layer.

- (UIImage *)imageFromLayer:(CALayer *)layer
{
    UIGraphicsBeginImageContext([layer frame].size);

    [layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return outputImage;
}

One more thing, there is one library available in github : CRGradientNavigationBar you can also use this library.

回答2:

Details

Xcode 8.3.1, Swift 3.1

Code

extension CAGradientLayer

extension CAGradientLayer {

    convenience init(frame: CGRect, colors: [UIColor]) {
        self.init()
        self.frame = frame
        self.colors = []
        for color in colors {
            self.colors?.append(color.cgColor)
        }
        startPoint = CGPoint(x: 0, y: 0)
        endPoint = CGPoint(x: 0, y: 1)
    }

    func createGradientImage() -> UIImage? {

        var image: UIImage? = nil
        UIGraphicsBeginImageContext(bounds.size)
        if let context = UIGraphicsGetCurrentContext() {
            render(in: context)
            image = UIGraphicsGetImageFromCurrentImageContext()
        }
        UIGraphicsEndImageContext()
        return image
    }

}

extension UINavigationBar

extension UINavigationBar {

    func setGradientBackground(colors: [UIColor]) {

        var updatedFrame = bounds
        updatedFrame.size.height += self.frame.origin.y
        let gradientLayer = CAGradientLayer(frame: updatedFrame, colors: colors)

        setBackgroundImage(gradientLayer.createGradientImage(), for: UIBarMetrics.default)
    }
}

Usage

class ViewController

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        var colors = [UIColor]()
        colors.append(UIColor(red: 221/255, green: 34/255, blue: 13/255, alpha: 1))
        colors.append(UIColor(red: 247/255, green: 113/255, blue: 98/255, alpha: 1))
        navigationController?.navigationBar.setGradientBackground(colors: colors)
    }
}

Main.storyboard

Result

回答3:

In Swift 3 and Swift 4:

let gradient = CAGradientLayer()
let sizeLength = UIScreen.main.bounds.size.height * 2
let defaultNavigationBarFrame = CGRect(x: 0, y: 0, width: sizeLength, height: 64)

gradient.frame = defaultNavigationBarFrame

gradient.colors = [UIColor.white.cgColor, UIColor.black.cgColor]

UINavigationBar.appearance().setBackgroundImage(self.image(fromLayer: gradient), for: .default)

For creating image from layer:

func image(fromLayer layer: CALayer) -> UIImage {
    UIGraphicsBeginImageContext(layer.frame.size)

    layer.render(in: UIGraphicsGetCurrentContext()!)

    let outputImage = UIGraphicsGetImageFromCurrentImageContext()

    UIGraphicsEndImageContext()

    return outputImage!
}

In Swift 2:

let gradient = CAGradientLayer()
let sizeLength = UIScreen.mainScreen().bounds.size.height * 2
let defaultNavigationBarFrame = CGRectMake(0, 0, sizeLength, 64)

gradient.frame = defaultNavigationBarFrame

gradient.colors = [UIColor.whiteColor().CGColor, UIColor.blackColor().CGColor]

UINavigationBar.appearance().setBackgroundImage(self.image(fromLayer: gradient), forBarMetrics: .Default)

For creating image from layer:

func image(fromLayer layer: CALayer) -> UIImage {    
    UIGraphicsBeginImageContext(layer.frame.size)

    layer.renderInContext(UIGraphicsGetCurrentContext()!)

    let outputImage = UIGraphicsGetImageFromCurrentImageContext()

     UIGraphicsEndImageContext()

    return outputImage!
}

回答4:

This is the solution without using an intermediate CAGradientLayer, and just using CoreGraphics, in Swift 3.0.

Essentially, the method creates a UIImage on the fly with the gradient colors passed and sets it.

extension UINavigationBar
{
    /// Applies a background gradient with the given colors
    func apply(gradient colors : [UIColor]) {
        var frameAndStatusBar: CGRect = self.bounds
        frameAndStatusBar.size.height += 20 // add 20 to account for the status bar

        setBackgroundImage(UINavigationBar.gradient(size: frameAndStatusBar.size, colors: colors), for: .default)
    }

    /// Creates a gradient image with the given settings
    static func gradient(size : CGSize, colors : [UIColor]) -> UIImage?
    {
        // Turn the colors into CGColors
        let cgcolors = colors.map { $0.cgColor }

        // Begin the graphics context
        UIGraphicsBeginImageContextWithOptions(size, true, 0.0)

        // If no context was retrieved, then it failed
        guard let context = UIGraphicsGetCurrentContext() else { return nil }

        // From now on, the context gets ended if any return happens
        defer { UIGraphicsEndImageContext() }

        // Create the Coregraphics gradient
        var locations : [CGFloat] = [0.0, 1.0]
        guard let gradient = CGGradient(colorsSpace: CGColorSpaceCreateDeviceRGB(), colors: cgcolors as NSArray as CFArray, locations: &locations) else { return nil }

        // Draw the gradient
        context.drawLinearGradient(gradient, start: CGPoint(x: 0.0, y: 0.0), end: CGPoint(x: size.width, y: 0.0), options: [])

        // Generate the image (the defer takes care of closing the context)
        return UIGraphicsGetImageFromCurrentImageContext()
    }
}

The defer statement makes this so much clean than prior versions. Be noted that CGGradient are available since iOS 8.0.

Also, this creates the gradient from left to right, tweaking the parameters of drawLinearGradient (start and end) moves the locations. This is up for your implementation.

回答5:

In Swift 3

let gradient = CAGradientLayer()
let sizeLength = UIScreen.main.bounds.size.height * 2
let defaultNavigationBarFrame = CGRect(x: 0, y: 0, width: sizeLength, height: 64)
gradient.frame = defaultNavigationBarFrame
gradient.colors = [UIColor.white.cgColor, UIColor.black.cgColor]
UINavigationBar.appearance().setBackgroundImage(self.image(fromLayer: gradient), for: .default)

func image(fromLayer layer: CALayer) -> UIImage {
    UIGraphicsBeginImageContext(layer.frame.size)
    layer.render(in: UIGraphicsGetCurrentContext()!)
    let outputImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return outputImage!
}

回答6:

For Swift 4.2

extension UINavigationBar {
    func setGradientBackground(colors: [Any]) {
        let gradient: CAGradientLayer = CAGradientLayer()
        gradient.locations = [0.0 , 0.5, 1.0]
        gradient.startPoint = CGPoint(x: 0.0, y: 1.0)
        gradient.endPoint = CGPoint(x: 1.0, y: 1.0)

        var updatedFrame = self.bounds
        updatedFrame.size.height += self.frame.origin.y
        gradient.frame = updatedFrame
        gradient.colors = colors;
        self.setBackgroundImage(self.image(fromLayer: gradient), for: .default)
    }

    func image(fromLayer layer: CALayer) -> UIImage {
        UIGraphicsBeginImageContext(layer.frame.size)
        layer.render(in: UIGraphicsGetCurrentContext()!)
        let outputImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return outputImage!
    }
}

How to use

   self.navigationController?.navigationBar.setGradientBackground(colors: [
            UIColor.red.cgColor,
            UIColor.green.cgColor,
            UIColor.blue.cgColor
            ])

回答7:

Objective C solution that works on iPhone X as well:

- (void)addGradientToNavigationBar
{
    CAGradientLayer *gradient = [CAGradientLayer layer];
    CGRect gradientFrame = self.navigationController.navigationBar.bounds;
    gradientFrame.size.height += [UIApplication sharedApplication].statusBarFrame.size.height;
    gradient.frame = gradientFrame;
    gradient.colors = [NSArray arrayWithObjects:(id)[[UIColor colorGradientUp] CGColor], (id)[[UIColor colorGradientDown] CGColor], nil];
    [self.navigationController.navigationBar setBackgroundImage:[self imageFromLayer:gradient] forBarMetrics:UIBarMetricsDefault];
}

- (UIImage *)imageFromLayer:(CALayer *)layer
{
    UIGraphicsBeginImageContext([layer frame].size);

    [layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return outputImage;
}