How can I create a horizontal gradient background

问题:

I know how to set a navigation bar background color (with barTintColor), but now I am working on an iOS app that calls for a horizontal gradient (not the typical vertical gradient).

How can I create a navigation bar with a horizontal gradient background?

回答1:

If you want to programmatically set the gradient of a given UINavigationBar I have a solution for you.

First setup a CAGradientLayer with your desired colors and locations.

CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = navigationBar.bounds;
gradientLayer.colors = @[ (__bridge id)[UIColor greenColor].CGColor,
                          (__bridge id)[UIColor blueColor].CGColor ];
gradientLayer.startPoint = CGPointMake(0.0, 0.5);
gradientLayer.endPoint = CGPointMake(1.0, 0.5);

Then grab the UImage for that layer.

UIGraphicsBeginImageContext(gradientLayer.bounds.size);
[gradientLayer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *gradientImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

Set the gradientImage as the backgroundImage for your UINavigationBar.

[navigationBar setBackgroundImage:gradientImage forBarMetrics:UIBarMetricsDefault];

Swift Solution:

[![// Setup the gradient
let gradientLayer = CAGradientLayer()
gradientLayer.frame = navigationBar.bounds
gradientLayer.colors = [UIColor.green.cgColor, UIColor.blue.cgColor]
gradientLayer.startPoint = CGPoint(x: 0.0, y: 0.5)
gradientLayer.endPoint = CGPoint(x: 1.0, y: 0.5)

// Render the gradient to UIImage
UIGraphicsBeginImageContext(gradientLayer.bounds.size)
gradientLayer.render(in: UIGraphicsGetCurrentContext()!)
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

 Set the UIImage as background property
navigationBar.setBackgroundImage(image, for: UIBarMetrics.default)

回答2:

Updated @JulianM answer for iOS 10 / swift 3.0:

let gradientLayer = CAGradientLayer()
var updatedFrame = self.navigationController!.navigationBar.bounds
updatedFrame.size.height += 20
gradientLayer.frame = updatedFrame
gradientLayer.colors = [UIColor.green.cgColor, UIColor.blue.cgColor]
gradientLayer.startPoint = CGPoint(x: 0.0, y: 0.5)
gradientLayer.endPoint = CGPoint(x: 1.0, y: 0.5)

UIGraphicsBeginImageContext(gradientLayer.bounds.size)
gradientLayer.render(in: UIGraphicsGetCurrentContext()!)
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

self.navigationController!.navigationBar.setBackgroundImage(image, for: UIBarMetrics.default)

回答3:

You can use that :

[[UINavigationBar appearance] setBackgroundImage:[UIImage imageNamed:@"gardientImage"] forBarMetrics:UIBarMetricsDefault];

for ios 7 navigation bar height is 64px