ios - Swift 圆形图像动画

Question

<分区>

Answer 1

您可以通过使用计时器调整 ImageView 上的蒙版来实现这一点。您应该使用一种特殊类型的计时器，即“显示链接”，它具有独特的时间以实现最佳屏幕更新。

例如:

class ViewController: UIViewController {

    @IBOutlet weak var imageView: UIImageView!

    weak var mask: CAShapeLayer?

    override func viewDidLoad() {
        super.viewDidLoad()

        // add mask to imageview and save reference to it

        let mask = CAShapeLayer()
        mask.fillColor = #colorLiteral(red: 1, green: 1, blue: 1, alpha: 1).cgColor
        mask.strokeColor = #colorLiteral(red: 1, green: 1, blue: 1, alpha: 0).cgColor
        imageView.layer.mask = mask
        self.mask = mask
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        // update the mask for the image view for the size of the view (which was unknown at `viewDidLoad`, but is known here)

        if mask != nil {
            updatePath(percent: 0)
        }
    }

    @IBAction func didTapButton(_ sender: Any) {
        // when we tap button, start display link which will drive the animation

        start = CACurrentMediaTime()
        let displayLink = CADisplayLink(target: self, selector: #selector(handleDisplaylink(_:)))
        displayLink.add(to: .main, forMode: .commonModes)
    }

    var start: CFTimeInterval!          // when the animation was started
    let duration: CFTimeInterval = 0.5  // how long will the animation take

    @objc func handleDisplaylink(_ displayLink: CADisplayLink) {
        // calculate, based upon elapsed time, how far along we are

        let percent = CGFloat(min(1, (CACurrentMediaTime() - start) / duration))

        // update the path based upon what percent of the animation has been completed

        updatePath(percent: percent)

        // if we're done, stop display link and go ahead and remove mask now that it's not needed any more

        if percent >= 1 {
            displayLink.invalidate()
            imageView.layer.mask = nil
        }
    }

    /// Update the circular mask for the image view based upon what percent of the animation is done

    private func updatePath(percent: CGFloat) {
        let center = CGPoint(x: imageView.bounds.midX, y: imageView.bounds.midY)
        let startRadius = min(imageView.bounds.width, imageView.bounds.height) * 0.4  // start radius is 40% of smallest dimension
        let endRadius = hypot(imageView.bounds.width, imageView.bounds.height) * 0.5  // stop radius is the distance from the center to the corner of the image view
        let radius = startRadius + (endRadius - startRadius) * percent                // given percent done, what is the radius

        mask?.path = UIBezierPath(arcCenter: center, radius: radius, startAngle: 0, endAngle: .pi * 2, clockwise: true).cgPath
    }

}

即实现: