老規矩先上圖和demo地址：

剛看到這個動畫的時候，腦海裡出現了兩個方案，一種是通過drawRect畫出來，然後配合CADisplayLink不停的繪制線的樣式；第二種是通過CAShapeLayer配合CAAnimation來實現動畫效果。再三考慮覺得使用後者，因為前者需要計算很多，比較復雜，而且經過測試前者相比於後者消耗更多的CPU，下面將我的思路寫下來：<喎?/kf/ware/vc/" target="_blank" class="keylink">vcD4NCjxoMSBpZD0="相關配置和初始化方法">相關配置和初始化方法

在寫這個動畫之前，我們把先需要的屬性寫好，比如線條的粗細，動畫的時間等等，下面是相關的配置和初識化方法：

    //線的寬度
    var lineWidth:CGFloat = 0
    //線的長度
    var lineLength:CGFloat = 0
    //邊距
    var margin:CGFloat = 0
    //動畫時間
    var duration:Double = 2
    //動畫的間隔時間
    var interval:Double = 1
    //四條線的顏色
    var colors:[UIColor] = [UIColor.init(rgba: "#9DD4E9") , UIColor.init(rgba: "#F5BD58"),  UIColor.init(rgba: "#FF317E") , UIColor.init(rgba: "#6FC9B5")]
    //動畫的狀態
    private(set) var status:AnimationStatus = .Normal
    //四條線
    private var lines:[CAShapeLayer] = []

    enum AnimationStatus {
        //普通狀態
        case Normal
        //動畫中
        case Animating
        //暫停
        case pause
    }

     //MARK: Initial Methods
    convenience init(fram: CGRect , colors: [UIColor]) {
        self.init()
        self.frame = frame
        self.colors = colors
        config()
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        config()
    }

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

    private func config() {
        lineLength = max(frame.width, frame.height)
        lineWidth  = lineLength/6.0
        margin     = lineLength/4.5 + lineWidth/2
        drawLineShapeLayer()
        transform = CGAffineTransformRotate(CGAffineTransformIdentity, angle(-30))
    }

通過CAShapeLayer繪制線條

看到這個線條我就想到了用CAShapeLayer來處理，因為CAShapeLayer完全可以實現這種效果，而且它的strokeEnd的屬性可以用來實現線條的長度變化的動畫，下面上繪制四根線條的代碼：

//MARK: 繪制線
    /**
     繪制四條線
     */
    private func drawLineShapeLayer() {
        //開始點
        let startPoint = [point(lineWidth/2, y: margin),
                          point(lineLength - margin, y: lineWidth/2),
                          point(lineLength - lineWidth/2, y: lineLength - margin),
                          point(margin, y: lineLength - lineWidth/2)]
        //結束點
        let endPoint   = [point(lineLength - lineWidth/2, y: margin) ,
                         point(lineLength - margin, y: lineLength - lineWidth/2) ,
                         point(lineWidth/2, y: lineLength - margin) ,
                         point(margin, y: lineWidth/2)]
        for i in 0...3 {
            let line:CAShapeLayer = CAShapeLayer()
            line.lineWidth   = lineWidth
            line.lineCap     = kCALineCapRound
            line.opacity     = 0.8
            line.strokeColor = colors[i].CGColor
            line.path        = getLinePath(startPoint[i], endPoint: endPoint[i]).CGPath
            layer.addSublayer(line)
            lines.append(line)
        }

    }

    /**
     獲取線的路徑

     - parameter startPoint: 開始點
     - parameter endPoint:   結束點

     - returns: 線的路徑
     */
    private func getLinePath(startPoint: CGPoint, endPoint: CGPoint) -> UIBezierPath {
        let path = UIBezierPath()
        path.moveToPoint(startPoint)
        path.addLineToPoint(endPoint)
        return path
    }

    private func point(x:CGFloat , y:CGFloat) -> CGPoint {
        return CGPointMake(x, y)
    }

    private func angle(angle: Double) -> CGFloat {
        return CGFloat(angle *  (M_PI/180))
    }

執行完後就跟上圖一樣的效果了~~~

動畫分解

經過分析，可以將動畫分為四個步驟：

畫布的旋轉動畫，旋轉兩圈 線條由長變短的動畫，更畫布選擇的動畫一起執行，旋轉一圈的時候結束 線條的位移動畫，線條逐漸向中間靠攏，再畫筆旋轉完一圈的時候執行，兩圈的時候結束 線條由短變長的動畫，畫布旋轉完兩圈的時候執行

第一步畫布旋轉動畫

這裡我們使用CABasicAnimation基礎動畫，keyPath作用於畫布的transform.rotation.z，以z軸為目標進行旋轉，下面是效果圖和代碼：

//MARK: 動畫步驟
    /**
     旋轉的動畫，旋轉兩圈
     */
    private func angleAnimation() {
        let angleAnimation                 = CABasicAnimation.init(keyPath: "transform.rotation.z")
        angleAnimation.fromValue           = angle(-30)
        angleAnimation.toValue             = angle(690)
        angleAnimation.fillMode            = kCAFillModeForwards
        angleAnimation.removedOnCompletion = false
        angleAnimation.duration            = duration
        angleAnimation.delegate            = self
        layer.addAnimation(angleAnimation, forKey: "angleAnimation")
    }

第二步線條由長變短的動畫

這裡我們還是使用CABasicAnimation基礎動畫，keyPath作用於線條的strokeEnd屬性，讓strokeEnd從1到0來實現線條長短的動畫，下面是效果圖和代碼：

/**
     線的第一步動畫，線長從長變短
     */
    private func lineAnimationOne() {
        let lineAnimationOne                 = CABasicAnimation.init(keyPath: "strokeEnd")
        lineAnimationOne.duration            = duration/2
        lineAnimationOne.fillMode            = kCAFillModeForwards
        lineAnimationOne.removedOnCompletion = false
        lineAnimationOne.fromValue           = 1
        lineAnimationOne.toValue             = 0
        for i in 0...3 {
            let lineLayer = lines[i]
            lineLayer.addAnimation(lineAnimationOne, forKey: "lineAnimationOne")
        }
    }

第三步線條的位移動畫

這裡我們也是使用CABasicAnimation基礎動畫，keyPath作用於線條的transform.translation.x和transform.translation.y屬性，來實現向中間聚攏的效果，下面是效果圖和代碼：

/**
     線的第二步動畫，線向中間平移
     */
    private func lineAnimationTwo() {
        for i in 0...3 {
            var keypath = "transform.translation.x"
            if i%2 == 1 {
                keypath = "transform.translation.y"
            }
            let lineAnimationTwo = CABasicAnimation.init(keyPath: keypath)
            lineAnimationTwo.beginTime = CACurrentMediaTime() + duration/2
            lineAnimationTwo.duration = duration/4
            lineAnimationTwo.fillMode = kCAFillModeForwards
            lineAnimationTwo.removedOnCompletion = false
            lineAnimationTwo.autoreverses = true
            lineAnimationTwo.fromValue = 0
            if i < 2 {
                lineAnimationTwo.toValue = lineLength/4
            }else {
                lineAnimationTwo.toValue = -lineLength/4
            }
            let lineLayer = lines[i]
            lineLayer.addAnimation(lineAnimationTwo, forKey: "lineAnimationTwo")
        }

        //三角形兩邊的比例
        let scale = (lineLength - 2*margin)/(lineLength - lineWidth)
        for i in 0...3 {
            var keypath = "transform.translation.y"
            if i%2 == 1 {
                keypath = "transform.translation.x"
            }
            let lineAnimationTwo = CABasicAnimation.init(keyPath: keypath)
            lineAnimationTwo.beginTime = CACurrentMediaTime() + duration/2
            lineAnimationTwo.duration = duration/4
            lineAnimationTwo.fillMode = kCAFillModeForwards
            lineAnimationTwo.removedOnCompletion = false
            lineAnimationTwo.autoreverses = true
            lineAnimationTwo.fromValue = 0
            if i == 0 || i == 3 {
                lineAnimationTwo.toValue = lineLength/4 * scale
            }else {
                lineAnimationTwo.toValue = -lineLength/4 * scale
            }
            let lineLayer = lines[i]
            lineLayer.addAnimation(lineAnimationTwo, forKey: "lineAnimationThree")
        }
    }

第四步線條恢復的原來長度的動畫

這裡我們還是使用CABasicAnimation基礎動畫，keyPath作用於線條的strokeEnd屬性，讓strokeEnd從0到1來實現線條長短的動畫，下面是效果圖和代碼：

/**
     線的第三步動畫，線由短變長
     */
    private func lineAnimationThree() {
        //線移動的動畫
        let lineAnimationFour                 = CABasicAnimation.init(keyPath: "strokeEnd")
        lineAnimationFour.beginTime            = CACurrentMediaTime() + duration
        lineAnimationFour.duration            = duration/4
        lineAnimationFour.fillMode            = kCAFillModeForwards
        lineAnimationFour.removedOnCompletion = false
        lineAnimationFour.fromValue           = 0
        lineAnimationFour.toValue             = 1
        for i in 0...3 {
            if i == 3 {
                lineAnimationFour.delegate = self
            }
            let lineLayer = lines[i]
            lineLayer.addAnimation(lineAnimationFour, forKey: "lineAnimationFour")
        }
    }

最後一步需要將動畫組合起來

關於動畫組合我沒用到CAAnimationGroup，因為這些動畫並不是加到同一個layer上，再加上動畫類型有點多加起來也比較麻煩，我就通過動畫的beginTime屬性來控制動畫的執行順序，還加了動畫暫停和繼續的功能，效果和代碼見下圖：

//MARK: Public Methods
    /**
     開始動畫
     */
    func startAnimation() {
        angleAnimation()
        lineAnimationOne()
        lineAnimationTwo()
        lineAnimationThree()
    }

    /**
      暫停動畫
     */
    func pauseAnimation() {
        layer.pauseAnimation()
        for lineLayer in lines {
            lineLayer.pauseAnimation()
        }
        status = .pause
    }

    /**
     繼續動畫
     */
    func resumeAnimation() {
        layer.resumeAnimation()
        for lineLayer in lines {
            lineLayer.resumeAnimation()
        }
        status = .Animating
    }

    extension CALayer {
    //暫停動畫
    func pauseAnimation() {
        // 將當前時間CACurrentMediaTime轉換為layer上的時間, 即將parent time轉換為localtime
        let pauseTime = convertTime(CACurrentMediaTime(), fromLayer: nil)
        // 設置layer的timeOffset, 在繼續操作也會使用到
        timeOffset    = pauseTime
        // localtime與parenttime的比例為0, 意味著localtime暫停了
        speed         = 0;
    }

    //繼續動畫
    func resumeAnimation() {
        let pausedTime = timeOffset
        speed          = 1
        timeOffset     = 0;
        beginTime      = 0
        // 計算暫停時間
        let sincePause = convertTime(CACurrentMediaTime(), fromLayer: nil) - pausedTime
        // local time相對於parent time時間的beginTime
        beginTime      = sincePause
    }
}

//MARK: Animation Delegate
    override func animationDidStart(anim: CAAnimation) {
        if let animation = anim as? CABasicAnimation {
            if animation.keyPath == "transform.rotation.z" {
                status = .Animating
            }
        }
    }

    override func animationDidStop(anim: CAAnimation, finished flag: Bool) {
        if let animation = anim as? CABasicAnimation {
            if animation.keyPath == "strokeEnd" {
                if flag {
                    status = .Normal
                    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(interval) * Int64(NSEC_PER_SEC)), dispatch_get_main_queue(), {
                        if self.status != .Animating {
                            self.startAnimation()
                        }
                    })
                }
            }
        }
    }

     //MARK: Override
    override func touchesEnded(touches: Set, withEvent event: UIEvent?) {
        switch status {
        case .Animating:
            pauseAnimation()
        case .pause:
            resumeAnimation()
        case .Normal:
            startAnimation()
        }
    }

總結

動畫看起來挺復雜，但是細細劃分出來也就那麼回事，在寫動畫之前要先想好動畫的步驟，這個很關鍵，希望大家通過這篇博客可以學到東西，有什麼好的建議可以隨時提出來，謝謝大家閱讀~~demo地址