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];
}

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)

SwiftUI:你可以使用线性梯度结构作为ZStack的第一个元素。作为ZStack的“底部”，它将作为背景色。AngularGradient和RadialGradient也可用。

import SwiftUI

struct ContentView: View {
    var body: some View {
        ZStack {
            LinearGradient(gradient: Gradient(colors: [.red, .blue]), startPoint: .top, endPoint: .bottom)
                .edgesIgnoringSafeArea(.all)
            // Put other content here; it will appear on top of the background gradient
        }
    }
}

你提供给渐变的颜色必须是CGColor类型。设置CGColor数组为gl。colors。

正确的代码是:

class Colors {
    var gl:CAGradientLayer!

    init() {
        let colorTop = UIColor(red: 192.0 / 255.0, green: 38.0 / 255.0, blue: 42.0 / 255.0, alpha: 1.0).cgColor
        let colorBottom = UIColor(red: 35.0 / 255.0, green: 2.0 / 255.0, blue: 2.0 / 255.0, alpha: 1.0).cgColor

        self.gl = CAGradientLayer()
        self.gl.colors = [colorTop, colorBottom]
        self.gl.locations = [0.0, 1.0]
    }
}

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

如果你有视图集合(多视图)，请这样做

  func setGradientBackground() {
    let v:UIView
    for v in viewgradian
    //here viewgradian is your view Collection Outlet name
    {
        let layer:CALayer
        var arr = [AnyObject]()
        for layer in v.layer.sublayers!
        {
           arr.append(layer)
        }

        let colorTop = UIColor(red: 216.0/255.0, green: 240.0/255.0, blue: 244.0/255.0, alpha: 1.0).cgColor
        let colorBottom = UIColor(red: 255.0/255.0, green: 255.0/255.0, blue: 255.0/255.0, alpha: 1.0).cgColor
        let gradientLayer = CAGradientLayer()
        gradientLayer.colors = [ colorBottom, colorTop]
        gradientLayer.startPoint = CGPoint(x: 1.0, y: 0.0)
        gradientLayer.endPoint = CGPoint(x: 0.0, y: 1.0)
        gradientLayer.frame = v.bounds
        v.layer.insertSublayer(gradientLayer, at: 0)
    }
}