本文是通过结合使用CAGradientLayer、CABasicAnimation以及CAAnimationDelegate来达到颜色渐变以及转换的动画，下面是今天要达成的效果图：
首先创建一个CAGradientLayer和几个自己喜欢的颜色，让VC持有。
let colorOne = #colorLiteral(red: 0.2392156869, green: 0.6745098233, blue: 0.9686274529, alpha: 1).cgColor
let colorTwo = #colorLiteral(red: 0.8078431487, green: 0.02745098062, blue: 0.3333333433, alpha: 1).cgColor
let colorThree = #colorLiteral(red: 0.9607843161, green: 0.7058823705, blue: 0.200000003, alpha: 1).cgColor
let gradient = CAGradientLayer()接下来为gradient赋值，将其frame等同于视图的大小，然后颜色先设置为colorOne和colorTwo，起始点和结束点分别为CGPoint(x:0, y:0)和CGPoint(x:1, y:1)，并设置让其在后台线程异步绘制，最后添加到view的layer的sublayer中。
gradient.frame = self.view.bounds
gradient.colors = [colorOne,colorTwo]
gradient.startPoint = CGPoint(x:0, y:0)
gradient.endPoint = CGPoint(x:1, y:1)
gradient.drawsAsynchronously = true
self.view.layer.insertSublayer(gradient, at: 0)现在运行后会得到下面的结果：
颜色渐变是做到了，那么如何做到颜色渐变的转换呢?这里还是需要用到CABasicAnimation.
在gradient创建完之后，添加并调用一个方法animateGradient，在里面添加一个keyPath为colors的CABasicAnimation，设置动画时长为3s，设置结束值等一系列属性。
func animateGradient() {
let gradientChangeAnimation = CABasicAnimation(keyPath: "colors")
gradientChangeAnimation.duration = 3.0
gradientChangeAnimation.toValue = [colorTwo,colorThree]
gradientChangeAnimation.fillMode = CAMediaTimingFillMode.forwards
gradientChangeAnimation.isRemovedOnCompletion = false
gradient.add(gradientChangeAnimation, forKey: "gradientChangeAnimation")
}这里就完成了转换动画。但是这里有个问题就是这里只转换了一次，无法转换多次颜色。那么这里就需要设置好toValue，让每次的toValue都不一样。
创建一个currentGradient和gradientSet让VC持有。
var currentGradient: Int = 0
var gradientSet = [[CGColor]]()在animateGradient中每次调用的时候，都对currentGradient的值进行判断和处理。
if currentGradient < gradientSet.count - 1 {
currentGradient += 1
} else {
currentGradient = 0
}并修改gradientChangeAnimation的toValue：
let gradientChangeAnimation = CABasicAnimation(keyPath: "colors")
gradientChangeAnimation.duration = 3.0
gradientChangeAnimation.toValue = gradientSet[currentGradient]
gradientChangeAnimation.fillMode = CAMediaTimingFillMode.forwards
gradientChangeAnimation.isRemovedOnCompletion = false
gradientChangeAnimation.repeatCount = Float.infinity
gradient.add(gradientChangeAnimation, forKey: "gradientChangeAnimation")这里运行后发现还是不行，还是只有一种颜色的转换，这是因为这里只调用了一次animateGradient()。那么如何在合适的时机，也就是动画结束的时候再调用一次animateGradient呢？这里就需要用到CAAnimationDelegate。
在CAAnimationDelegate的animationDidStop方法中重新调用animateGradient。注意这里的gradient.colors 也要改变，否则就会一直是[colorOne, colorTwo]到其他颜色的变换。
func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
// if our gradient animation ended animating, restart the animation by changing the color set
if flag {
gradient.colors = gradientSet[currentGradient]
animateGradient()
}
}完整代码：
import UIKit
class ViewController: UIViewController, CAAnimationDelegate {
let colorOne = #colorLiteral(red: 0.2392156869, green: 0.6745098233, blue: 0.9686274529, alpha: 1).cgColor
let colorTwo = #colorLiteral(red: 0.8078431487, green: 0.02745098062, blue: 0.3333333433, alpha: 1).cgColor
let colorThree = #colorLiteral(red: 0.9607843161, green: 0.7058823705, blue: 0.200000003, alpha: 1).cgColor
let gradient = CAGradientLayer()
var currentGradient: Int = 0
var gradientSet = [[CGColor]]()
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
NotificationCenter.default.addObserver(self, selector: #selector(handleEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
createGradientView()
}
@objc private func handleEnterForeground() {
animateGradient()
}
func animateGradient() {
// cycle through all the colors, feel free to add more to the set
if currentGradient < gradientSet.count - 1 {
currentGradient += 1
} else {
currentGradient = 0
}
// animate over 3 seconds
let gradientChangeAnimation = CABasicAnimation(keyPath: "colors")
gradientChangeAnimation.duration = 3.0
gradientChangeAnimation.toValue = gradientSet[currentGradient]
gradientChangeAnimation.fillMode = CAMediaTimingFillMode.forwards
gradientChangeAnimation.isRemovedOnCompletion = false
//gradientChangeAnimation.repeatCount = Float.infinity
gradientChangeAnimation.delegate = self
gradient.add(gradientChangeAnimation, forKey: "gradientChangeAnimation")
}
func createGradientView() {
// overlap the colors and make it 3 sets of colors
gradientSet.append([colorOne, colorTwo])
gradientSet.append([colorTwo, colorThree])
gradientSet.append([colorThree, colorOne])
// set the gradient size to be the entire screen
gradient.frame = self.view.bounds
gradient.colors = gradientSet[currentGradient]
gradient.startPoint = CGPoint(x:0, y:0)
gradient.endPoint = CGPoint(x:1, y:1)
gradient.drawsAsynchronously = true
self.view.layer.insertSublayer(gradient, at: 0)
animateGradient()
}
func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
// if our gradient animation ended animating, restart the animation by changing the color set
if flag {
gradient.colors = gradientSet[currentGradient]
animateGradient()
}
}
}以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持编程网。
