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。
