从案例出发，由浅到深了解 iOS 动画

收录：原文地址

前言

iOS 的动画框架很成熟，提供必要的信息，譬如动画的起始位置与终止位置，动画效果就出来了

动画的实现方式挺多的，

有系统提供的简单 API ，直接提供动画般的交互效果。

有手动设置交互效果，看起来像是动画，一般要用到插值。

至于动画框架，有 UIView 级别的，有功能强劲的 CALayer 级别的动画。

CALayer 级别的动画通过灵活设置的 CoreAnimation，CoreAnimation 的常规操作，就是自定义路径

当然有苹果推了几年的 UIViewPropertyAnimator， 动画可交互性做得比较好；

话不多说；直接来看案例

• • *

例子一：导航栏动画

navigationController?.hidesBarsOnSwipe = true

简单设置 hidesBarsOnSwipe 属性，就可以了。

该属性，除了可以调节头部导航栏，还可以调节底部标签工具栏 toolbar

• • *

例子二：屏幕开锁效果

一眼看起来有点炫，实际设置很简单

func openLock() {
        UIView.animate(withDuration: 0.4, delay: 1.0, options: [], animations: {

            // Rotate keyhole.
            self.lockKeyhole.transform = CGAffineTransform(rotationAngle: CGFloat.pi)

            }, completion: { _ in

                UIView.animate(withDuration: 0.5, delay: 0.2, options: [], animations: {

                    // Open lock.
                    let yDelta = self.lockBorder.frame.maxY

                    self.topLock.center.y -= yDelta
                    self.lockKeyhole.center.y -= yDelta
                    self.lockBorder.center.y -= yDelta
                    self.bottomLock.center.y += yDelta

                    }, completion: { _ in
                        self.topLock.removeFromSuperview()
                        self.lockKeyhole.removeFromSuperview()
                        self.lockBorder.removeFromSuperview()
                        self.bottomLock.removeFromSuperview()
                })
        })
    }

总共有四个控件，先让中间的锁控件旋转一下，然后对四个控件，做移位操作

用简单的关键帧动画，处理要优雅一点

• • *

例子三：地图定位波动

看上去有些眼花的动画，可以分解为三个动画

一波未平，一波又起，做一个动画效果的叠加，就成了动画的第一幅动画

一个动画波动效果，效果用到了透明度的变化，还有范围的变化

范围的变化，用的就是 CoreAnimation 的路径 path

CoreAnimation 简单设置，就是指明 from 、to，动画的起始状态，和动画终止状态，然后选择使用哪一种动画效果。

动画的起始状态，一般是起始位置。简单的动画，就是让他动起来

func sonar(_ beginTime: CFTimeInterval) {
        let circlePath1 = UIBezierPath(arcCenter: self.center, radius: CGFloat(3), startAngle: CGFloat(0), endAngle:CGFloat.pi * 2, clockwise: true)

        let circlePath2 = UIBezierPath(arcCenter: self.center, radius: CGFloat(80), startAngle: CGFloat(0), endAngle:CGFloat.pi * 2, clockwise: true)

        let shapeLayer = CAShapeLayer()
        shapeLayer.strokeColor = ColorPalette.green.cgColor
        shapeLayer.fillColor = ColorPalette.green.cgColor
        shapeLayer.path = circlePath1.cgPath
        self.layer.addSublayer(shapeLayer)

        // 两个动画

        let pathAnimation = CABasicAnimation(keyPath: "path")
        pathAnimation.fromValue = circlePath1.cgPath
        pathAnimation.toValue = circlePath2.cgPath

        let alphaAnimation = CABasicAnimation(keyPath: "opacity")
        alphaAnimation.fromValue = 0.8
        alphaAnimation.toValue = 0

        // 组动画
        let animationGroup = CAAnimationGroup()
        animationGroup.beginTime = beginTime
        animationGroup.animations = [pathAnimation, alphaAnimation]

        // 时间有讲究
        animationGroup.duration = 2.76

        // 不断重复
        animationGroup.repeatCount = Float.greatestFiniteMagnitude
        animationGroup.isRemovedOnCompletion = false
        animationGroup.fillMode = CAMediaTimingFillMode.forwards

        // Add the animation to the layer.
        // key 用来 debug
        shapeLayer.add(animationGroup, forKey: "sonar")
    }

波动效果调用了三次

func startAnimation() {
        // 三次动画，效果合成，
        sonar(CACurrentMediaTime())
        sonar(CACurrentMediaTime() + 0.92)
        sonar(CACurrentMediaTime() + 1.84)
    }

• • *

例子四：加载动画

这是 UIView 框架自带的动画，看起来不错，就是做了一个简单的缩放，通过 transform 属性做仿射变换

func startAnimation() {

        dotOne.transform = CGAffineTransform(scaleX: 0.01, y: 0.01)
        dotTwo.transform = CGAffineTransform(scaleX: 0.01, y: 0.01)
        dotThree.transform = CGAffineTransform(scaleX: 0.01, y: 0.01)

        // 三个不同的 delay, 渐进时间
        UIView.animate(withDuration: 0.6, delay: 0.0, options: [.repeat, .autoreverse], animations: {
            self.dotOne.transform = CGAffineTransform.identity
            }, completion: nil)

        UIView.animate(withDuration: 0.6, delay: 0.2, options: [.repeat, .autoreverse], animations: {
            self.dotTwo.transform = CGAffineTransform.identity
            }, completion: nil)

        UIView.animate(withDuration: 0.6, delay: 0.4, options: [.repeat, .autoreverse], animations: {
            self.dotThree.transform = CGAffineTransform.identity
            }, completion: nil)
    }

• • *

例子五：下划线点击转移动画

这个也是 UIView 的动画

动画的实现效果，是通过更改约束。

约束动画要注意的是，确保动画的起始位置准确，起始的时候，一般要调用其父视图的 layoutIfNeeded 方法，确保视图的实际位置与约束设置的一致。

这里的约束动画，是通过 NSLayoutAnchor 做得。

一般我们用的是 SnapKit 设置约束，调用也差不多。

func animateContraintsForUnderlineView(_ underlineView: UIView, toSide: Side) {

        switch toSide {
        case .left:

            for constraint in underlineView.superview!.constraints {
                if constraint.identifier == ConstraintIdentifiers.centerRightConstraintIdentifier {

                    constraint.isActive = false

                    let leftButton = optionsBar.arrangedSubviews[0]
                    let centerLeftConstraint = underlineView.centerXAnchor.constraint(equalTo: leftButton.centerXAnchor)
                    centerLeftConstraint.identifier = ConstraintIdentifiers.centerLeftConstraintIdentifier

                    NSLayoutConstraint.activate([centerLeftConstraint])
                }
            }

        case .right:

            for constraint in underlineView.superview!.constraints {
                if constraint.identifier == ConstraintIdentifiers.centerLeftConstraintIdentifier {
                    // 先失效，旧的约束
                    constraint.isActive = false
                    // 再新建约束，并激活
                    let rightButton = optionsBar.arrangedSubviews[1]
                    let centerRightConstraint = underlineView.centerXAnchor.constraint(equalTo: rightButton.centerXAnchor)
                    centerRightConstraint.identifier = ConstraintIdentifiers.centerRightConstraintIdentifier

                    NSLayoutConstraint.activate([centerRightConstraint])

                }
            }
        }

        UIView.animate(withDuration: 0.6, delay: 0.0, usingSpringWithDamping: 0.6, initialSpringVelocity: 0.0, options: [], animations: {
            self.view.layoutIfNeeded()
            }, completion: nil)

    }

• • *

例子六：列表视图的头部拉伸效果

这个没有用到动画框架，就是做了一个交互插值

就是补插连续的函数 scrollViewDidScroll, 及时更新列表视图头部的位置、尺寸

override func scrollViewDidScroll(_ scrollView: UIScrollView) {
        updateHeaderView()
    }

    func updateHeaderView() {
        var headerRect = CGRect(x: 0, y: -tableHeaderHeight, width: tableView.bounds.width, height: tableHeaderHeight)
        // 决定拉动的方向
        if tableView.contentOffset.y < -tableHeaderHeight {
            // 就是改 frame
            headerRect.origin.y = tableView.contentOffset.y
            headerRect.size.height = -tableView.contentOffset.y
        }

        headerView.frame = headerRect
    }

• • *

例子七：进度绘制动画

用到了 CoreAnimation，也用到了插值。

每一段插值都是一个 CoreAnimation 动画，进度的完成分为多次插值。

这里动画效果的主要用到 strokeEnd 属性, 笔画结束

插值的时候，要注意，下一段动画的开始，正是上一段动画的结束

// 这个用来，主要的效果
    let progressLayer = CAShapeLayer()
   // 这个用来，附加的颜色
    let gradientLayer = CAGradientLayer()

    // 给个默认值，外部设置
    var range: CGFloat = 128

    var curValue: CGFloat = 0 {
        didSet {
            animateStroke()
        }
    }

    func setupLayers() {

        progressLayer.position = CGPoint.zero
        progressLayer.lineWidth = 3.0
        progressLayer.strokeEnd = 0.0
        progressLayer.fillColor = nil
        progressLayer.strokeColor = UIColor.black.cgColor

        let radius = CGFloat(bounds.height/2) - progressLayer.lineWidth
        let startAngle = CGFloat.pi * (-0.5)
        let endAngle = CGFloat.pi * 1.5

        let width = bounds.width
        let height = bounds.height
        let modelCenter = CGPoint(x: width / 2, y: height / 2)
        let path = UIBezierPath(arcCenter: modelCenter, radius: radius, startAngle: startAngle, endAngle: endAngle, clockwise: true)
        //  指定路径
        progressLayer.path = path.cgPath

        layer.addSublayer(progressLayer)
        // 有一个渐变
        gradientLayer.frame = CGRect(x: 0.0, y: 0.0, width: bounds.width, height: bounds.height)

        //  teal, 蓝绿色

        gradientLayer.colors = [ColorPalette.teal.cgColor, ColorPalette.orange.cgColor, ColorPalette.pink.cgColor]
        gradientLayer.startPoint = CGPoint(x: 0.5, y: 0)
        gradientLayer.endPoint = CGPoint(x: 0.5, y: 1)

        gradientLayer.mask = progressLayer // Use progress layer as mask for gradient layer.
        layer.addSublayer(gradientLayer)
    }

    func animateStroke() {
        // 前一段的终点
        let fromValue = progressLayer.strokeEnd
        let toValue = curValue / range

        let animation = CABasicAnimation(keyPath: "strokeEnd")
        animation.fromValue = fromValue
        animation.toValue = toValue
        progressLayer.add(animation, forKey: "stroke")
        progressLayer.strokeEnd = toValue
    }

}

// 动画路径，结合插值

• • *

例子八：渐变动画

这个渐变动画，主要用到了渐变图层 CAGradientLayer 的 locations 位置属性，用来调整渐变区域的分布

另一个关键点是用了图层 CALayer 的遮罩 mask,

简单理解，把渐变图层全部蒙起来，只露出文本的形状，就是那几个字母的痕迹

class LoadingLabel: UIView {

    let gradientLayer: CAGradientLayer = {
        let gradientLayer = CAGradientLayer()

        gradientLayer.startPoint = CGPoint(x: 0.0, y: 0.5)
        gradientLayer.endPoint = CGPoint(x: 1.0, y: 0.5)

        // 灰， 白， 灰
        let colors = [UIColor.gray.cgColor, UIColor.white.cgColor, UIColor.gray.cgColor]
        gradientLayer.colors = colors

        let locations = [0.25, 0.5, 0.75]
        gradientLayer.locations = locations as [NSNumber]?

        return gradientLayer
    }()

    // 文字转图片，然后绘制到视图上

    // 通过设置渐变图层的遮罩 `mask` , 为指定文字，来设置渐变闪烁的效果

    @IBInspectable var text: String! {
          didSet {
               setNeedsDisplay()

                UIGraphicsBeginImageContextWithOptions(frame.size, false, 0)
                text.draw(in: bounds, withAttributes: textAttributes)
                let image = UIGraphicsGetImageFromCurrentImageContext()
                UIGraphicsEndImageContext()
               // 从文字中，抽取图片

                 let maskLayer = CALayer()
                 maskLayer.backgroundColor = UIColor.clear.cgColor
                 maskLayer.frame = bounds.offsetBy(dx: bounds.size.width, dy: 0)
                 maskLayer.contents = image?.cgImage

                 gradientLayer.mask = maskLayer
            }
      }

    // 设置位置与尺寸
    override func layoutSubviews() {
        gradientLayer.frame = CGRect(x: -bounds.size.width, y: bounds.origin.y, width: 2 * bounds.size.width, height: bounds.size.height)
    }

    override func didMoveToWindow() {
        super.didMoveToWindow()

        layer.addSublayer(gradientLayer)

        let gradientAnimation = CABasicAnimation(keyPath: "locations")
        gradientAnimation.fromValue = [0.0, 0.0, 0.25]
        gradientAnimation.toValue = [0.75, 1.0, 1.0]
        gradientAnimation.duration = 1.7

        // 一直循环
        gradientAnimation.repeatCount = Float.infinity
        gradientAnimation.isRemovedOnCompletion = false
        gradientAnimation.fillMode = CAMediaTimingFillMode.forwards

        gradientLayer.add(gradientAnimation, forKey: nil)
    }

}

• • *

例子九：下拉刷新动画

首先通过方法 scrollViewDidScroll 和 scrollViewWillEndDragging 做插值

extension PullRefreshView: UIScrollViewDelegate{

    // MARK: - UIScrollViewDelegate

       func scrollViewDidScroll(_ scrollView: UIScrollView) {
           let offsetY = CGFloat(max(-(scrollView.contentOffset.y + scrollView.contentInset.top), 0.0))
           self.progress = min(max(offsetY / frame.size.height, 0.0), 1.0)

           // 做互斥的状态管理
           if !isRefreshing {
               redrawFromProgress(self.progress)
           }
       }

       func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
           if !isRefreshing && self.progress >= 1.0 {
               delegate?.PullRefreshViewDidRefresh(self)
               beginRefreshing()
           }
       }

}

画面中飞碟动来动去，是通过 CAKeyframeAnimation(keyPath: "position") ，关键帧动画的位置属性，设置的

func redrawFromProgress(_ progress: CGFloat) {

        /* PART 1 ENTER ANIMATION */

        let enterPath = paths.start

        // 动画指定路径走
        let pathAnimation = CAKeyframeAnimation(keyPath: "position")
        pathAnimation.path = enterPath.cgPath
        pathAnimation.calculationMode = CAAnimationCalculationMode.paced
        pathAnimation.timingFunctions = [CAMediaTimingFunction(name: CAMediaTimingFunctionName.easeOut)]
        pathAnimation.beginTime = 1e-100

        pathAnimation.duration = 1.0
        pathAnimation.timeOffset = CFTimeInterval() + Double(progress)
        pathAnimation.isRemovedOnCompletion = false
        pathAnimation.fillMode = CAMediaTimingFillMode.forwards

        flyingSaucerLayer.add(pathAnimation, forKey: nil)
        flyingSaucerLayer.position = enterPath.currentPoint

        let sizeAlongEnterPathAnimation = CABasicAnimation(keyPath: "transform.scale")
        sizeAlongEnterPathAnimation.fromValue = 0
        sizeAlongEnterPathAnimation.toValue = progress
        sizeAlongEnterPathAnimation.beginTime = 1e-100

        sizeAlongEnterPathAnimation.duration = 1.0
        sizeAlongEnterPathAnimation.isRemovedOnCompletion = false
        sizeAlongEnterPathAnimation.fillMode = CAMediaTimingFillMode.forwards

        flyingSaucerLayer.add(sizeAlongEnterPathAnimation, forKey: nil)

    }

//  设置路径
   func customPaths(frame: CGRect = CGRect(x: 4, y: 3, width: 166, height: 74)) -> ( UIBezierPath, UIBezierPath) {

        // 两条路径

        let startY = 0.09459 * frame.height
        let enterPath = UIBezierPath()
        // ...
        enterPath.addCurve(to: CGPoint(x: frame.minX + 0.21694 * frame.width, y: frame.minY + 0.85855 * frame.height), controlPoint1: CGPoint(x: frame.minX + 0.04828 * frame.width, y: frame.minY + 0.68225 * frame.height), controlPoint2: CGPoint(x: frame.minX + 0.21694 * frame.width, y: frame.minY + 0.85855 * frame.height))

        enterPath.addCurve(to: CGPoint(x: frame.minX + 0.36994 * frame.width, y: frame.minY + 0.92990 * frame.height), controlPoint1: CGPoint(x: frame.minX + 0.21694 * frame.width, y: frame.minY + 0.85855 * frame.height), controlPoint2: CGPoint(x: frame.minX + 0.33123 * frame.width, y: frame.minY + 0.93830 * frame.height))
        // ...
        enterPath.usesEvenOddFillRule = true

        let exitPath = UIBezierPath()
        exitPath.move(to: CGPoint(x: frame.minX + 0.98193 * frame.width, y: frame.minY + 0.15336 * frame.height))
        exitPath.addLine(to: CGPoint(x: frame.minX + 0.51372 * frame.width, y: frame.minY + 0.28558 * frame.height))
        // ... 
        exitPath.miterLimit = 4
        exitPath.usesEvenOddFillRule = true

        return (enterPath, exitPath)
    }

}

这个动画比较复杂，需要做大量的数学计算，还要调试，具体看文尾的 git repo.

一般这种动画，我们用 Lottie

• • *

例子十：文本变换动画

这个动画有些复杂，重点使用了 CoreAnimation 的组动画，叠加了五种效果，缩放、尺寸、布局、位置与透明度。

具体看文尾的 git repo.

class func animation(_ layer: CALayer, duration: TimeInterval, delay: TimeInterval, animations: (() -> ())?, completion: ((_ finished: Bool)-> ())?) {

        let animation = CLMLayerAnimation()

        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + Double(Int64(delay * Double(NSEC_PER_SEC))) / Double(NSEC_PER_SEC)) {

            var animationGroup: CAAnimationGroup?
            let oldLayer = self.animatableLayerCopy(layer)
            animation.completionClosure = completion

            if let layerAnimations = animations {
                CATransaction.begin()
                CATransaction.setDisableActions(true)
                layerAnimations()
                CATransaction.commit()
            }

            animationGroup = groupAnimationsForDifferences(oldLayer, newLayer: layer)

            if let differenceAnimation = animationGroup {
                differenceAnimation.timingFunction = CAMediaTimingFunction(name: CAMediaTimingFunctionName.easeInEaseOut)
                differenceAnimation.duration = duration
                differenceAnimation.beginTime = CACurrentMediaTime()
                layer.add(differenceAnimation, forKey: nil)
            }
            else {
                if let completion = animation.completionClosure {
                    completion(true)
                }
            }

        }        
    }

    class func groupAnimationsForDifferences(_ oldLayer: CALayer, newLayer: CALayer) -> CAAnimationGroup? {
        var animationGroup: CAAnimationGroup?
        var animations = [CABasicAnimation]()

        // 叠加了五种效果

        if !CATransform3DEqualToTransform(oldLayer.transform, newLayer.transform) {
            let animation = CABasicAnimation(keyPath: "transform")
            animation.fromValue = NSValue(caTransform3D: oldLayer.transform)
            animation.toValue = NSValue(caTransform3D: newLayer.transform)
            animations.append(animation)
        }

        if !oldLayer.bounds.equalTo(newLayer.bounds) {
            let animation = CABasicAnimation(keyPath: "bounds")
            animation.fromValue = NSValue(cgRect: oldLayer.bounds)
            animation.toValue = NSValue(cgRect: newLayer.bounds)
            animations.append(animation)
        }

        if !oldLayer.frame.equalTo(newLayer.frame) {
            let animation = CABasicAnimation(keyPath: "frame")
            animation.fromValue = NSValue(cgRect: oldLayer.frame)
            animation.toValue = NSValue(cgRect: newLayer.frame)
            animations.append(animation)
        }

        if !oldLayer.position.equalTo(newLayer.position) {
            let animation = CABasicAnimation(keyPath: "position")
            animation.fromValue = NSValue(cgPoint: oldLayer.position)
            animation.toValue = NSValue(cgPoint: newLayer.position)
            animations.append(animation)
        }

        if oldLayer.opacity != newLayer.opacity {
            let animation = CABasicAnimation(keyPath: "opacity")
            animation.fromValue = oldLayer.opacity
            animation.toValue = newLayer.opacity
            animations.append(animation)
        }

        if animations.count > 0 {
            animationGroup = CAAnimationGroup()
            animationGroup!.animations = animations
        }

        return animationGroup
    }

• • *

例子十一：动态图动画

从 gif 文件里面取出每桢图片，算出持续时间，设置动画图片

internal class func animatedImageWithSource(_ source: CGImageSource) -> UIImage? {

        // 需要喂图片，
        // 喂动画持续时间

        let count = CGImageSourceGetCount(source)

        var data: (images: [CGImage], delays: [Int]) = ([CGImage](), [Int]())

        // Fill arrays
        for i in 0..<count {
            // Add image
            if let image = CGImageSourceCreateImageAtIndex(source, i, nil) {
                data.images.append(image)
            }

            let delaySeconds = UIImage.delayForImageAtIndex(Int(i),
                source: source)
            data.delays.append(Int(delaySeconds * 1000.0)) // Seconds to ms
        }

        // Calculate full duration
        let duration: Int = {
            var sum = 0
            for val: Int in data.delays {
                sum += val
            }
            return sum
        }()

        let gcd = gcdForArray(data.delays)
        var frames = [UIImage]()

        var frame: UIImage
        var frameCount: Int
        for i in 0..<count {
            frame = UIImage(cgImage: data.images[Int(i)])
            frameCount = Int(data.delays[Int(i)] / gcd)

            for _ in 0..<frameCount {
                frames.append(frame)
            }
        }

        let animation = UIImage.animatedImage(with: frames,
            duration: Double(duration) / 1000.0)

        return animation
    }

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