swift實現顏色漸變以及轉換動畫
本文是通過結合使用CAGradientLayer、CABasicAnimation以及CAAnimationDelegate來達到顏色漸變以及轉換的動畫，下面是今天要達成的效果圖：
首先創建一個CAGradientLayer和幾個自己喜歡的顏色，讓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()
接下來為gradient賦值，將其frame等同於視圖的大小，然後顏色先設置為colorOne和colorTwo，起始點和結束點分別為CGPoint(x:0, y:0)和CGPoint(x:1, y:1)，並設置讓其在後臺線程異步繪制，最後添加到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)
現在運行後會得到下面的結果：
顏色漸變是做到瞭，那麼如何做到顏色漸變的轉換呢?這裡還是需要用到CABasicAnimation.
在gradient創建完之後，添加並調用一個方法animateGradient，在裡面添加一個keyPath為colors的CABasicAnimation，設置動畫時長為3s，設置結束值等一系列屬性。
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")
}
這裡就完成瞭轉換動畫。但是這裡有個問題就是這裡隻轉換瞭一次，無法轉換多次顏色。那麼這裡就需要設置好toValue，讓每次的toValue都不一樣。
創建一個currentGradient和gradientSet讓VC持有。
var currentGradient: Int = 0 var gradientSet = [[CGColor]]()
在animateGradient中每次調用的時候，都對currentGradient的值進行判斷和處理。
if currentGradient < gradientSet.count - 1 {
currentGradient += 1
} else {
currentGradient = 0
}
並修改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")
這裡運行後發現還是不行，還是隻有一種顏色的轉換，這是因為這裡隻調用瞭一次animateGradient()。那麼如何在合適的時機，也就是動畫結束的時候再調用一次animateGradient呢？這裡就需要用到CAAnimationDelegate。
在CAAnimationDelegate的animationDidStop方法中重新調用animateGradient。註意這裡的gradient.colors 也要改變，否則就會一直是[colorOne, colorTwo]到其他顏色的變換。
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()
}
}
完整代碼：
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內容，希望對大傢的學習有所幫助，也希望大傢多多支持WalkonNet。