快速的方法

This answer builds on the answers above and provides implementation for dealing with the problem of the gradient not being properly applied during rotation. It satisfies this problem by changing the gradient layer to a square so that rotation in all directions results in a correct gradient. The function signature includes a Swift variadic argument that allows one to pass in as many CGColorRef's (CGColor) as needed (see sample usage). Also provided is an example as a Swift extension so that one can apply a gradient to any UIView.

   func configureGradientBackground(colors:CGColorRef...){

        let gradient: CAGradientLayer = CAGradientLayer()
        let maxWidth = max(self.view.bounds.size.height,self.view.bounds.size.width)
        let squareFrame = CGRect(origin: self.view.bounds.origin, size: CGSizeMake(maxWidth, maxWidth))
        gradient.frame = squareFrame

        gradient.colors = colors
        view.layer.insertSublayer(gradient, atIndex: 0)
    }

使用方法:

在viewDidLoad ...

  override func viewDidLoad() {
        super.viewDidLoad()
        configureGradientBackground(UIColor.redColor().CGColor, UIColor.whiteColor().CGColor)
  }

扩展的实现

extension CALayer {


    func configureGradientBackground(colors:CGColorRef...){

        let gradient = CAGradientLayer()

        let maxWidth = max(self.bounds.size.height,self.bounds.size.width)
        let squareFrame = CGRect(origin: self.bounds.origin, size: CGSizeMake(maxWidth, maxWidth))
        gradient.frame = squareFrame

        gradient.colors = colors

        self.insertSublayer(gradient, atIndex: 0)
    }

}

扩展用例示例:

 override func viewDidLoad() {
        super.viewDidLoad()

        self.view.layer.configureGradientBackground(UIColor.purpleColor().CGColor, UIColor.blueColor().CGColor, UIColor.whiteColor().CGColor)
 }

这意味着渐变背景现在可以应用到任何UIControl，因为所有的控件都是UIViews(或子类)，所有的UIViews都有calayer。

斯威夫特4

扩展的实现

extension CALayer {
    public func configureGradientBackground(_ colors:CGColor...){

        let gradient = CAGradientLayer()

        let maxWidth = max(self.bounds.size.height,self.bounds.size.width)
        let squareFrame = CGRect(origin: self.bounds.origin, size: CGSize(width: maxWidth, height: maxWidth))
        gradient.frame = squareFrame

        gradient.colors = colors

        self.insertSublayer(gradient, at: 0)
    }    
}

扩展用例示例:

override func viewDidLoad() {
    super.viewDidLoad()

    self.view.layer.configureGradientBackground(UIColor.purple.cgColor, UIColor.blue.cgColor, UIColor.white.cgColor)
}

你要找的是CAGradientLayer。每个UIView都有一个层-在这个层中你可以添加子层，就像你可以添加子视图一样。一个特定的类型是CAGradientLayer，在这里你给它一个颜色数组来渐变。

一个例子是这个简单的渐变视图包装器:

http://oleb.net/blog/2010/04/obgradientview-a-simple-uiview-wrapper-for-cagradientlayer/

注意，为了访问UIView的所有层部分，你需要包括QuartZCore框架。

在Swift 3.1中 我已经添加了这个扩展到UIView

import Foundation
import UIKit
import CoreGraphics


extension UIView {
    func gradientOfView(withColours: UIColor...) {

        var cgColours = [CGColor]()

        for colour in withColours {
            cgColours.append(colour.cgColor)
        }
        let grad = CAGradientLayer()
        grad.frame = self.bounds
        grad.colors = cgColours
        self.layer.insertSublayer(grad, at: 0)
    }
}

然后我用它来调用

    class OverviewVC: UIViewController {

        override func viewDidLoad() {
            super.viewDidLoad()

            self.view.gradientOfView(withColours: UIColor.red,UIColor.green, UIColor.blue)

        }
}

objective - c:

UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 50)];
CAGradientLayer *gradient = [CAGradientLayer layer];

gradient.frame = view.bounds;
gradient.colors = @[(id)[UIColor whiteColor].CGColor, (id)[UIColor blackColor].CGColor];

[view.layer insertSublayer:gradient atIndex:0];

迅速:

let view = UIView(frame: CGRect(x: 0, y: 0, width: 320, height: 50))
let gradient = CAGradientLayer()

gradient.frame = view.bounds
gradient.colors = [UIColor.white.cgColor, UIColor.black.cgColor]

view.layer.insertSublayer(gradient, at: 0)

信息:使用startPoint和endPoint改变梯度的方向。

如果有任何其他视图添加到这个UIView(比如一个UILabel)，你可能想要考虑设置那些UIView的背景色为[UIColor clearColor]，这样渐变视图就会呈现而不是子视图的背景色。使用clearColor会对性能造成轻微的影响。

这是我推荐的方法。

为了提高可重用性，我建议创建一个CAGradientLayer类别，并添加所需的渐变作为类方法。在头文件中像这样指定它们:

#import <QuartzCore/QuartzCore.h>

@interface CAGradientLayer (SJSGradients)

+ (CAGradientLayer *)redGradientLayer;
+ (CAGradientLayer *)blueGradientLayer;
+ (CAGradientLayer *)turquoiseGradientLayer;
+ (CAGradientLayer *)flavescentGradientLayer;
+ (CAGradientLayer *)whiteGradientLayer;
+ (CAGradientLayer *)chocolateGradientLayer;
+ (CAGradientLayer *)tangerineGradientLayer;
+ (CAGradientLayer *)pastelBlueGradientLayer;
+ (CAGradientLayer *)yellowGradientLayer;
+ (CAGradientLayer *)purpleGradientLayer;
+ (CAGradientLayer *)greenGradientLayer;

@end

然后在你的实现文件中，用下面的语法指定每个渐变:

+ (CAGradientLayer *)flavescentGradientLayer
{
    UIColor *topColor = [UIColor colorWithRed:1 green:0.92 blue:0.56 alpha:1];
    UIColor *bottomColor = [UIColor colorWithRed:0.18 green:0.18 blue:0.18 alpha:1];

    NSArray *gradientColors = [NSArray arrayWithObjects:(id)topColor.CGColor, (id)bottomColor.CGColor, nil];
    NSArray *gradientLocations = [NSArray arrayWithObjects:[NSNumber numberWithInt:0.0],[NSNumber numberWithInt:1.0], nil];

    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.colors = gradientColors;
    gradientLayer.locations = gradientLocations;

    return gradientLayer;
}

然后简单地将这个类别导入你的ViewController或任何其他所需的子类，并像这样使用它:

CAGradientLayer *backgroundLayer = [CAGradientLayer purpleGradientLayer];
backgroundLayer.frame = self.view.frame;
[self.view.layer insertSublayer:backgroundLayer atIndex:0];

我已经在代码中实现了这一点。

UIView *view1 = [[UIView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, self.view.frame.size.width, 31.0f)];
view1.backgroundColor = [UIColor clearColor];
CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = view1.bounds;
UIColor *topColor = [UIColor colorWithRed:132.0/255.0 green:222.0/255.0 blue:109.0/255.0 alpha:1.0];
UIColor *bottomColor = [UIColor colorWithRed:31.0/255.0 green:150.0/255.0 blue:99.0/255.0 alpha:1.0];
gradient.colors = [NSArray arrayWithObjects:(id)[topColor CGColor], (id)[bottomColor CGColor], nil];


[view1.layer insertSublayer:gradient atIndex:0];

现在我可以在视图中看到渐变。