ios - 动画期间的 UIView 中心位置

Question

我想确定，动画期间 UIVIew( View 的中间点)的中心位置是什么。像这样的带有 UIViewPropertyAnimator 的动画:

let animator = UIViewPropertyAnimator(duration: 10, curve: .easeInOut)
 
var circle : UIView!
circle = UIView(frame: CGRect(x: 0.0, y: 0.0, width: 40.0, height: 40.0))
circle.layer.cornerRadius = 20.0
circle.backgroundColor = UIColor.blue
self.view.addSubview(circle)

animator.addAnimations {
    circle.center = CGPoint(x: 100,y: 100)
    //or any other point
}
animator.startAnimation()

如果我在动画期间打印 circle.center 属性，那么我得到的只是动画的目标位置，而不是实际位置。

Timer.scheduledTimer(withTimeInterval: 0.2, repeats: true, block: {
[weak self] (Timer) -> Void in
if let circleCenterPosition = self?.circle.center
{
    print(circleCenterPosition)
}
})

打印后我在控制台上看到了这个:

(100.0, 100.0)

(100.0, 100.0)

...

如何打印动画中的真实位置？

谢谢。

Answer 1

我想出了一个可能的答案。

CALayer有一个 presentation() 函数

func presentation() Returns a copy of the presentation layer object that represents the state of the layer as it currently appears onscreen.

表示层有一个框架属性，即 CGRect，从这里可以轻松计算中点。

演示

代码

class ViewController: UIViewController {
        var circle : UIView!
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        let animator = UIViewPropertyAnimator(duration: 10, curve: .easeInOut)
        circle = UIView(frame: CGRect(x: 0.0, y: 0.0, width: 40.0, height: 40.0))
        circle.layer.cornerRadius = 20.0
        circle.backgroundColor = UIColor.blue
        self.view.addSubview(circle)
        Timer.scheduledTimer(withTimeInterval: 0.2, repeats: true)
        {
            [weak self] (myTimer) -> Void in
            if let movingBlueDotFrame = self?.circle.layer.presentation()?.frame
            {
                let blueDotOriginPoint = movingBlueDotFrame.origin
                let blueDotMiddlePoint = CGPoint(x: blueDotOriginPoint.x + movingBlueDotFrame.width/2, y: blueDotOriginPoint.y + movingBlueDotFrame.height/2)
                print(blueDotMiddlePoint)
                if blueDotMiddlePoint == CGPoint(x:100,y:100){
                    print("Yeeaahh")
                    myTimer.invalidate()
                }
            }
       }
        animator.addAnimations {
            self.circle.center = CGPoint(x: 100,y: 100)
        }
        animator.startAnimation()
    }
}

想法来自这里UIView animation determine center during animation

如果您有更简单或更好的解决方案，请在下面添加。谢谢!