一、前言

随着开发者的增多和时间的累积，AppStore已经有非常多的应用了，每年都有很多新的APP产生。但是我们手机上留存的应用有限，所以如何吸引用户，成为产品设计的一项重要内容。其中炫酷的动画效果是重要内容之一，我们会发现很多好的应用上面都有许多很炫的效果。可能一提到炫酷的动画，很多人都很头疼，因为动画并不是那么好做，实现一个好的动画需要时间、耐心和好的思路。下面我们就以一个有趣的动画（如下图）为例，抽丝剥茧，看看到底是怎么实现的！

二、分析

上面图中的动画第一眼看起来的确是有点复杂，但是我们来一步步分析，就会发现其实并不是那么难。仔细看一下就会发现，大致步骤如下：

• 1、先出来一个圆
• 2、圆形在水平和竖直方向上被挤压，呈椭圆形状的一个过程，最后恢复成圆形
• 3、圆形的左下角、右下角和顶部分别按顺序凸出一小部分
• 4、圆和凸出部分形成的图形旋转一圈后变成三角形
• 5、三角形的左边先后出来两条宽线，将三角形围在一个矩形中
• 6、矩形由底部向上被波浪状填满
• 7、被填满的矩形放大至全屏，弹出Welcome

动画大致就分为上面几个步骤，拆分后我们一步步来实现其中的效果（下面所示步骤中以Swift代码为例，demo中分别有Objective-C和Swift的实现）。

三、实现圆形以及椭圆的渐变

首先，我们创建了一个新工程后，然后新建了一个名AnimationView的类继承UIView，这个是用来显示动画效果的一个view。然后先添加CircleLayer（圆形layer），随后实现由小变大的效果。

 class AnimationView: UIView {

      let circleLayer = CircleLayer()

      override init(frame: CGRect) {
           super.init(frame: frame)
           backgroundColor = UIColor.clearColor()
           addCircleLayer()
       }

      required init?(coder aDecoder: NSCoder) {
           super.init(coder: aDecoder)
       }

      /**
       add circle layer
       */
      func addCircleLayer() {
           self.layer.addSublayer(circleLayer)
           circleLayer.expand()
       }
  }

其中expand()这个方法如下

    /**
     expand animation function
     */
    func expand() {
        let expandAnimation: CABasicAnimation = CABasicAnimation(keyPath: "path")
        expandAnimation.fromValue = circleSmallPath.CGPath
        expandAnimation.toValue = circleBigPath.CGPath
        expandAnimation.duration = KAnimationDuration
        expandAnimation.fillMode = kCAFillModeForwards
        expandAnimation.removedOnCompletion = false
        self.addAnimation(expandAnimation, forKey: nil)
    }

运行效果如下

第一步做好了，接下来就是呈椭圆形状的变化了，仔细分析就比如一个弹性小球，竖直方向捏一下，水平方向捏一下这样的效果。这其实就是一个组合动画，如下

    /**
     wobbl group animation
     */
    func wobbleAnimate() {
        // 1、animation begin from bigPath to verticalPath
        let animation1: CABasicAnimation = CABasicAnimation(keyPath: "path")
        animation1.fromValue = circleBigPath.CGPath
        animation1.toValue = circleVerticalSquishPath.CGPath
        animation1.beginTime = KAnimationBeginTime
        animation1.duration = KAnimationDuration

        // 2、animation vertical to horizontal
        let  animation2: CABasicAnimation = CABasicAnimation(keyPath: "path")
        animation2.fromValue = circleVerticalSquishPath.CGPath
        animation2.toValue = circleHorizontalSquishPath.CGPath
        animation2.beginTime = animation1.beginTime + animation1.duration
        animation2.duration = KAnimationDuration

        // 3、animation horizontal to vertical
        let  animation3: CABasicAnimation = CABasicAnimation(keyPath: "path")
        animation3.fromValue = circleHorizontalSquishPath.CGPath
        animation3.toValue = circleVerticalSquishPath.CGPath
        animation3.beginTime = animation2.beginTime + animation2.duration
        animation3.duration = KAnimationDuration

        // 4、animation vertical to bigPath
        let  animation4: CABasicAnimation = CABasicAnimation(keyPath: "path")
        animation4.fromValue = circleVerticalSquishPath.CGPath
        animation4.toValue = circleBigPath.CGPath
        animation4.beginTime = animation3.beginTime + animation3.duration
        animation4.duration = KAnimationDuration

        // 5、group animation
        let animationGroup: CAAnimationGroup = CAAnimationGroup()
        animationGroup.animations = [animation1, animation2, animation3, animation4]
        animationGroup.duration = 4 * KAnimationDuration
        animationGroup.repeatCount = 2
        addAnimation(animationGroup, forKey: nil)
    }

上面代码中实现了从 圆 → 椭圆（x方向长轴）→ 椭圆（y方向长轴）→ 圆这一系列的变化，最后组合成一个动画。这一步实现后效果如下

四、实现圆形边缘的凸出部分

关于这个凸出部分，乍一看可能感觉会比较难实现，看起来挺复杂的。其实实现的原理很简单，仔细分析我们会发现这三个凸出部分连起来刚好是一个三角形，那么第一步我们就在之前的基础上先加一个三角形的layer，如下

import UIKit

class TriangleLayer: CAShapeLayer {

    let paddingSpace: CGFloat = 30.0

    override init() {
         super.init()
        fillColor = UIColor.colorWithHexString("#009ad6").CGColor
        strokeColor = UIColor.colorWithHexString("#009ad6").CGColor
        lineWidth = 7.0
        path = smallTrianglePath.CGPath
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    var smallTrianglePath: UIBezierPath {
        let smallPath = UIBezierPath()
        smallPath.moveToPoint(CGPointMake(5.0 + paddingSpace, 95.0))
        smallPath.addLineToPoint(CGPointMake(50.0, 12.5 + paddingSpace))
        smallPath.addLineToPoint(CGPointMake(95.0 - paddingSpace, 95.0))
        smallPath.closePath()
        return smallPath
    }
}

然后设置圆角

        lineCap = kCALineCapRound
        lineJoin = kCALineJoinRound

下面就是来做凸出部分了，原理其实很简单，就是将现在这个三角形保持中心不变，左边向左延伸即可

然后同理，保持中心不变分别按顺序向右和向上拉伸

具体过程是这样的

    /**
     triangle animate function
     */
    func triangleAnimate() {
         // left
        let triangleAnimationLeft: CABasicAnimation = CABasicAnimation(keyPath: "path")
        triangleAnimationLeft.fromValue = smallTrianglePath.CGPath
        triangleAnimationLeft.toValue = leftTrianglePath.CGPath
        triangleAnimationLeft.beginTime = 0.0
        triangleAnimationLeft.duration = 0.3
         // right
        let triangleAnimationRight: CABasicAnimation = CABasicAnimation(keyPath: "path")
        triangleAnimationRight.fromValue = leftTrianglePath.CGPath
        triangleAnimationRight.toValue = rightTrianglePath.CGPath
        triangleAnimationRight.beginTime = triangleAnimationLeft.beginTime + triangleAnimationLeft.duration
        triangleAnimationRight.duration = 0.25
         // top
        let triangleAnimationTop: CABasicAnimation = CABasicAnimation(keyPath: "path")
        triangleAnimationTop.fromValue = rightTrianglePath.CGPath
        triangleAnimationTop.toValue = topTrianglePath.CGPath
        triangleAnimationTop.beginTime = triangleAnimationRight.beginTime + triangleAnimationRight.duration
        triangleAnimationTop.duration = 0.20
         // group
        let triangleAnimationGroup: CAAnimationGroup = CAAnimationGroup()
        triangleAnimationGroup.animations = [triangleAnimationLeft, triangleAnimationRight, triangleAnimationTop]
        triangleAnimationGroup.duration = triangleAnimationTop.beginTime + triangleAnimationTop.duration
        triangleAnimationGroup.fillMode = kCAFillModeForwards
        triangleAnimationGroup.removedOnCompletion = false
        addAnimation(triangleAnimationGroup, forKey: nil)
    }

我们接下来把三角形的颜色改一下

这里颜色相同了我们就可以看到了这个凸出的这个效果，调到正常速率（为了演示，把动画速率调慢了） ，联合之前所有的动作，到现在为止，效果是这样的

到现在为止，看上去还不错，差不多已经完成一半了，继续下一步！

五、实现旋转和矩形

旋转来说很简单了，大家估计都做过旋转动画，这里就是把前面形成的图形旋转一下（当然要注意设置锚点anchorPoint）

    /**
     self transform z
     */
    func transformRotationZ() {
        self.layer.anchorPoint = CGPointMake(0.5, 0.65)
        let rotationAnimation: CABasicAnimation = CABasicAnimation(keyPath: "transform.rotation.z")
        rotationAnimation.toValue = CGFloat(M_PI * 2)
        rotationAnimation.duration = 0.45
        rotationAnimation.removedOnCompletion = true
        layer.addAnimation(rotationAnimation, forKey: nil)
    }

旋转之后原图形被切成了一个三角形，思路就是把原来的大圆，按着这个大三角形的内切圆剪切一下即可

    /**
     contract animation function
     */
    func contract() {
        let contractAnimation: CABasicAnimation = CABasicAnimation(keyPath: "path")
        contractAnimation.fromValue = circleBigPath.CGPath
        contractAnimation.toValue = circleSmallPath.CGPath
        contractAnimation.duration = KAnimationDuration
        contractAnimation.fillMode = kCAFillModeForwards
        contractAnimation.removedOnCompletion = false
        addAnimation(contractAnimation, forKey: nil)
    }

接下来就是画矩形，新建一个RectangleLayer，划线

    /**
     line stroke color change with custom color

     - parameter color: custom color
     */
    func strokeChangeWithColor(color: UIColor) {
        strokeColor = color.CGColor
        let strokeAnimation: CABasicAnimation = CABasicAnimation(keyPath: "strokeEnd")
        strokeAnimation.fromValue = 0.0
        strokeAnimation.toValue = 1.0
        strokeAnimation.duration = 0.4
        addAnimation(strokeAnimation, forKey: nil)
    }

最后面就是经典的水波纹动画了，不多说，直接上代码

    func animate() {
         /// 1
        let waveAnimationPre: CABasicAnimation = CABasicAnimation(keyPath: "path")
        waveAnimationPre.fromValue = wavePathPre.CGPath
        waveAnimationPre.toValue = wavePathStarting.CGPath
        waveAnimationPre.beginTime = 0.0
        waveAnimationPre.duration = KAnimationDuration
         /// 2
        let waveAnimationLow: CABasicAnimation = CABasicAnimation(keyPath: "path")
        waveAnimationLow.fromValue = wavePathStarting.CGPath
        waveAnimationLow.toValue = wavePathLow.CGPath
        waveAnimationLow.beginTime = waveAnimationPre.beginTime + waveAnimationPre.duration
        waveAnimationLow.duration = KAnimationDuration
         /// 3
        let waveAnimationMid: CABasicAnimation = CABasicAnimation(keyPath: "path")
        waveAnimationMid.fromValue = wavePathLow.CGPath
        waveAnimationMid.toValue = wavePathMid.CGPath
        waveAnimationMid.beginTime = waveAnimationLow.beginTime + waveAnimationLow.duration
        waveAnimationMid.duration = KAnimationDuration
         /// 4
        let waveAnimationHigh: CABasicAnimation = CABasicAnimation(keyPath: "path")
        waveAnimationHigh.fromValue = wavePathMid.CGPath
        waveAnimationHigh.toValue = wavePathHigh.CGPath
        waveAnimationHigh.beginTime = waveAnimationMid.beginTime + waveAnimationMid.duration
        waveAnimationHigh.duration = KAnimationDuration
         /// 5
        let waveAnimationComplete: CABasicAnimation = CABasicAnimation(keyPath: "path")
        waveAnimationComplete.fromValue = wavePathHigh.CGPath
        waveAnimationComplete.toValue = wavePathComplete.CGPath
        waveAnimationComplete.beginTime = waveAnimationHigh.beginTime + waveAnimationHigh.duration
        waveAnimationComplete.duration = KAnimationDuration
         /// group animation
        let arcAnimationGroup: CAAnimationGroup = CAAnimationGroup()
        arcAnimationGroup.animations = [waveAnimationPre, waveAnimationLow, waveAnimationMid, waveAnimationHigh, waveAnimationComplete]
        arcAnimationGroup.duration = waveAnimationComplete.beginTime + waveAnimationComplete.duration
        arcAnimationGroup.fillMode = kCAFillModeForwards
        arcAnimationGroup.removedOnCompletion = false
        addAnimation(arcAnimationGroup, forKey: nil)
    }

找几个点控制水波形状，画出贝塞尔曲线即可，到这里基本就完成了。接下来最后一步，放大，并弹出Welcome

    func expandView() {
        backgroundColor = UIColor.colorWithHexString("#40e0b0")
        frame = CGRectMake(frame.origin.x - blueRectangleLayer.lineWidth,
                           frame.origin.y - blueRectangleLayer.lineWidth,
                           frame.size.width + blueRectangleLayer.lineWidth * 2,
                           frame.size.height + blueRectangleLayer.lineWidth * 2)
        layer.sublayers = nil

        UIView.animateWithDuration(0.3, delay: 0.0, options: UIViewAnimationOptions.CurveEaseInOut, animations: {
            self.frame = self.parentFrame
            }, completion: { finished in
                self.delegate?.completeAnimation()
        })

    }

放大完以后设置代理，然后在主的vc中添加Welcome这个Label

    // MARK: -
    // MARK: AnimationViewDelegate
    func completeAnimation() {
        // 1
        animationView.removeFromSuperview()
        view.backgroundColor = UIColor.colorWithHexString("#40e0b0")

        // 2
        let label: UILabel = UILabel(frame: view.frame)
        label.textColor = UIColor.whiteColor()
        label.font = UIFont(name: "HelveticaNeue-Thin", size: 50.0)
        label.textAlignment = NSTextAlignment.Center
        label.text = "Welcome"
        label.transform = CGAffineTransformScale(label.transform, 0.25, 0.25)
        view.addSubview(label)

        // 3
        UIView.animateWithDuration(0.4, delay: 0.0, usingSpringWithDamping: 0.7, initialSpringVelocity: 0.1, options: UIViewAnimationOptions.CurveEaseInOut,animations: ({

                label.transform = CGAffineTransformScale(label.transform, 4.0, 4.0)
            }), completion: { finished in
                self.addTouchButton()
        })

    }

到现在为止，动画全部完成

六、最后

同样，还是提供了两个版本（Objective-C & Swift），你可以在 这里 查看源码！
一直对动画比较感兴趣，希望多研究多深入，有什么意见或者建议的话，可以留言或者私信，如果觉得还好的话，请star支持，谢谢！