用这个自定义类扩展UIView。

GradientView.swift

import UIKit

class GradientView: UIView {

    // Default Colors
    var colors:[UIColor] = [UIColor.redColor(), UIColor.blueColor()]

    override func drawRect(rect: CGRect) {

        // Must be set when the rect is drawn
        setGradient(colors[0], color2: colors[1])
    }

    func setGradient(color1: UIColor, color2: UIColor) {

        let context = UIGraphicsGetCurrentContext()
        let gradient = CGGradientCreateWithColors(CGColorSpaceCreateDeviceRGB(), [color1.CGColor, color2.CGColor], [0, 1])!

        // Draw Path
        let path = UIBezierPath(rect: CGRectMake(0, 0, frame.width, frame.height))
        CGContextSaveGState(context)
        path.addClip()
        CGContextDrawLinearGradient(context, gradient, CGPointMake(frame.width / 2, 0), CGPointMake(frame.width / 2, frame.height), CGGradientDrawingOptions())
        CGContextRestoreGState(context)
    }

    override func layoutSubviews() {

        // Ensure view has a transparent background color (not required)
        backgroundColor = UIColor.clearColor()
    }

}

使用

gradientView。colors = [uiccolor . blackcolor ().colorWithAlphaComponent(0.8)， uiccolor . clearcolor ()]

结果

对于那些想要Objective C版本的答案的人。经过测试，在iOS13上运行

// Done here so that constraints have completed and the frame is correct.
- (void) viewDidLayoutSubviews { 
    [super viewDidLayoutSubviews];
    UIColor *colorTop = [UIColor colorWithRed:(CGFloat)192.0/255.0 green: 38.0/255.0 blue: 42.0/255.0 alpha:1.0];
    UIColor *colorBottom = [UIColor colorWithRed: 35.0/255.0 green: 2.0/255.0 blue: 2.0/255.0 alpha: 1.0];
    CAGradientLayer *gl = [CAGradientLayer new];
    [gl setColors:@[(id)[colorTop CGColor], (id)[colorBottom CGColor]]];
    [gl setLocations:@[@0.0f, @1.0f]];
    self.view.backgroundColor = [UIColor clearColor];
    CALayer *backgroundLayer = gl;
    backgroundLayer.frame = self.view.frame;
    [self.view.layer insertSublayer:backgroundLayer atIndex:0];
}

我注意到的一件事是，你不能在不清除文本的情况下给UILabel添加渐变。一个简单的解决方法是使用UIButton并禁用用户交互。

Swift 3 -只使用纹理和SKSpriteNode，不需要UIView

import Foundation
import SpriteKit

class GradientSpriteNode : SKSpriteNode
{
    convenience init(size: CGSize, colors: [UIColor], locations: [CGFloat])
    {
        let texture = GradientSpriteNode.texture(size: size, colors: colors, locations: locations)
        self.init(texture: texture, color:SKColor.clear, size: texture.size())
    }

    private override init(texture: SKTexture!, color: SKColor, size: CGSize) {
        super.init(texture: texture, color: color, size: size)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    private static func texture(size: CGSize, colors: [UIColor], locations: [CGFloat]) -> SKTexture
    {
        UIGraphicsBeginImageContext(size)
        let context = UIGraphicsGetCurrentContext()!
        let gradient = CGGradient(colorsSpace: CGColorSpaceCreateDeviceRGB(), colors: colors.map{$0.cgColor} as CFArray, locations: locations)!
        context.drawLinearGradient(gradient, start: CGPoint(x: size.width / 2, y: 0), end: CGPoint(x: size.width / 2, y: size.height), options: CGGradientDrawingOptions())
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return SKTexture(image: image!)

    }
}

用法:

let gradient = GradientSpriteNode(
        size: CGSize(width: 100, height: 100),
        colors: [UIColor.red, UIColor.blue],
        locations: [0.0, 1.0])
addChild(gradient)

只需要指定视图的框架，你想在其中显示渐变颜色。

let firstColor =  UIColor(red: 69/255, green: 90/255, blue: 195/255, alpha: 1.0).CGColor

 let secondColor = UIColor(red: 230/255, green: 44/255, blue: 75/255, alpha: 1.0).CGColor

    let gradientLayer = CAGradientLayer()
    gradientLayer.colors = [ firstColor, secondColor]
    gradientLayer.locations = [ 0.0, 1.0]
    gradientLayer.frame = CGRectMake(0, 0, 375, 64)// You can mention frame here

    self.view.layer.addSublayer(gradientLayer)

有一个名为Chameleon (https://github.com/viccalexander/Chameleon)的库可以用于渐变颜色。它甚至有渐变的风格来实现。这就是如何在swift 4 podfile中添加它 “变色龙框架/Swift”，:git => 'https://github.com/ViccAlexander/Chameleon.git'，:branch => 'wip/swift4'

import ChameleonFramework

let colors:[UIColor] = [
  UIColor.flatPurpleColorDark(), 
  UIColor.flatWhiteColor()
]
view.backgroundColor = GradientColor(.TopToBottom, frame: view.frame, colors: colors)