cakeyframeanimation - 如何获取 CAKeyframeAnimation 对象的当前屏幕 xy 位置？

Question

在 iOS 12 beta 12 下的 Swift 4.2 中，我想获取我在CAKeyframeAnimation.

动画的代码是这样的：

    @IBOutlet weak var dot: UIImageView!

    func animateDot() {        
        // Oval path.
        let ovalWidth = UIScreen.main.bounds.width * 0.7
        let ovalHeight = UIScreen.main.bounds.height * 0.75
        let ovalPath = UIBezierPath(ovalIn: CGRect(x: -ovalWidth / 2 , y: -ovalHeight / 2, width: ovalWidth, height: ovalHeight))
        let orbit = CAKeyframeAnimation(keyPath: "position")
        orbit.path = ovalPath.cgPath
        orbit.duration = CFTimeInterval(2.5)
        orbit.isAdditive = true
        orbit.repeatCount = 6
        orbit.calculationMode = kCAAnimationPaced
        orbit.rotationMode = kCAAnimationRotateAuto

        self.dot.layer.add(orbit, forKey: "orbit")
    }

我的问题是：一旦启动并运行，如何在 Swift 中查询动画以获取点中心的当前屏幕 xy？

Answer 1

我发现可以查询与点关联的活动表示层以获取边界点当前位置的框架：

        if (self.dot.layer.presentation() != nil)
        {
            let dotLocation = self.dot.layer.presentation()?.frame
            os_log("self.dot.layer.presentation()?.frame.minX %12f", type: .debug, dotLocation!.minX)
            os_log("self.dot.layer.presentation()?.frame.maxX %12f", type: .debug, dotLocation!.maxX)
            os_log("self.dot.layer.presentation()?.frame.minY %12f", type: .debug, dotLocation!.minY)
            os_log("self.dot.layer.presentation()?.frame.maxY %12f", type: .debug, dotLocation!.maxY)

            var dotScreenLocation: CGPoint = CGPoint(x: 0, y: 0)
            dotScreenLocation.x = dotLocation!.minX + ((dotLocation!.maxX - dotLocation!.minX) / 2)
            dotScreenLocation.y = dotLocation!.minY + ((dotLocation!.maxY - dotLocation!.minY) / 2)
            os_log("self.dot.layer.presentation()?.frame center x,y %12f,%12f", type: .debug, dotScreenLocation.x, dotScreenLocation.y)
}