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

如果你想使用HEX而不是RGBA，只需拖动一个新的空的.swift并添加下面提到的代码:

     import UIKit

    extension UIColor {
        convenience init(rgba: String) {
            var red:   CGFloat = 0.0
            var green: CGFloat = 0.0
            var blue:  CGFloat = 0.0
            var alpha: CGFloat = 1.0

            if rgba.hasPrefix("#") {
                let index   = advance(rgba.startIndex, 1)
                let hex     = rgba.substringFromIndex(index)
                let scanner = NSScanner(string: hex)
                var hexValue: CUnsignedLongLong = 0
                if scanner.scanHexLongLong(&hexValue) {
                    switch (count(hex)) {
                    case 3:
                        red   = CGFloat((hexValue & 0xF00) >> 8)       / 15.0
                        green = CGFloat((hexValue & 0x0F0) >> 4)       / 15.0
                        blue  = CGFloat(hexValue & 0x00F)              / 15.0
                    case 4:
                        red   = CGFloat((hexValue & 0xF000) >> 12)     / 15.0
                        green = CGFloat((hexValue & 0x0F00) >> 8)      / 15.0
                        blue  = CGFloat((hexValue & 0x00F0) >> 4)      / 15.0
                        alpha = CGFloat(hexValue & 0x000F)             / 15.0
                    case 6:
                        red   = CGFloat((hexValue & 0xFF0000) >> 16)   / 255.0
                        green = CGFloat((hexValue & 0x00FF00) >> 8)    / 255.0
                        blue  = CGFloat(hexValue & 0x0000FF)           / 255.0
                    case 8:
                        red   = CGFloat((hexValue & 0xFF000000) >> 24) / 255.0
                        green = CGFloat((hexValue & 0x00FF0000) >> 16) / 255.0
                        blue  = CGFloat((hexValue & 0x0000FF00) >> 8)  / 255.0
                        alpha = CGFloat(hexValue & 0x000000FF)         / 255.0
                    default:
                        print("Invalid RGB string, number of characters after '#' should be either 3, 4, 6 or 8")
                    }
                } else {
                    println("Scan hex error")
                }
            } else {
                print("Invalid RGB string, missing '#' as prefix")
            }
            self.init(red:red, green:green, blue:blue, alpha:alpha)
        }
}

类似地，拖动另一个空的.swift文件并添加下面提到的代码:

    class Colors {
    let colorTop = UIColor(rgba: "##8968CD").CGColor
    let colorBottom = UIColor(rgba: "#5D478B").CGColor

    let gl: CAGradientLayer

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

然后在视图控制器中，在类下面实例化你的Color类，像这样:

let colors = Colors()

添加一个新函数:

func refresh() {
        view.backgroundColor = UIColor.clearColor()
        var backgroundLayer = colors.gl
        backgroundLayer.frame = view.frame
        view.layer.insertSublayer(backgroundLayer, atIndex: 0)
    }

在viewDidLoad中声明函数:

refresh()

你完成了:)) 如果与RGBA相比，使用HEX太容易了。: D

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)

在Swift3试试这个:

 func addGradient(){

    let gradient:CAGradientLayer = CAGradientLayer()
    gradient.frame.size = self.viewThatHoldsGradient.frame.size
    gradient.colors = [UIColor.white.cgColor,UIColor.white.withAlphaComponent(0).cgColor] //Or any colors
    self.viewThatHoldsGradient.layer.addSublayer(gradient)

}

易于使用的扩展swift 3

extension CALayer {
    func addGradienBorder(colors:[UIColor] = [UIColor.red,UIColor.blue], width:CGFloat = 1) {
        let gradientLayer = CAGradientLayer()
        gradientLayer.frame =  CGRect(origin: .zero, size: self.bounds.size)
        gradientLayer.startPoint = CGPoint(x:0.0, y:0.5)
        gradientLayer.endPoint = CGPoint(x:1.0, y:0.5)
        gradientLayer.colors = colors.map({$0.cgColor})

        let shapeLayer = CAShapeLayer()
        shapeLayer.lineWidth = width
        shapeLayer.path = UIBezierPath(rect: self.bounds).cgPath
        shapeLayer.fillColor = nil
        shapeLayer.strokeColor = UIColor.black.cgColor
        gradientLayer.mask = shapeLayer

        self.addSublayer(gradientLayer)
    }
}

用你的观点，例子

yourView.addGradienBorder(color: UIColor.black, opacity: 0.1, offset: CGSize(width:2 , height: 5), radius: 3, viewCornerRadius: 3.0)

我做了一个UIView扩展应用一个基本的渐变到任何视图

extension UIView {
    func layerGradient() {
        let layer : CAGradientLayer = CAGradientLayer()
        layer.frame.size = self.frame.size
        layer.frame.origin = CGPointMake(0.0,0.0)
        layer.cornerRadius = CGFloat(frame.width / 20)

        let color0 = UIColor(red:250.0/255, green:250.0/255, blue:250.0/255, alpha:0.5).CGColor
        let color1 = UIColor(red:200.0/255, green:200.0/255, blue: 200.0/255, alpha:0.1).CGColor
        let color2 = UIColor(red:150.0/255, green:150.0/255, blue: 150.0/255, alpha:0.1).CGColor
        let color3 = UIColor(red:100.0/255, green:100.0/255, blue: 100.0/255, alpha:0.1).CGColor
        let color4 = UIColor(red:50.0/255, green:50.0/255, blue:50.0/255, alpha:0.1).CGColor
        let color5 = UIColor(red:0.0/255, green:0.0/255, blue:0.0/255, alpha:0.1).CGColor
        let color6 = UIColor(red:150.0/255, green:150.0/255, blue:150.0/255, alpha:0.1).CGColor

        layer.colors = [color0,color1,color2,color3,color4,color5,color6]
        self.layer.insertSublayer(layer, atIndex: 0)
    }
}