UIView center position during animation

Question

I would like to determine, what is the center position of a UIVIew (the middle point of the view) during an animation. An animation with UIViewPropertyAnimator like this:

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()

If I print the circle.center property during the animation then I got just the destination position of the animation not the real position.

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

After this print I saw this on the console:

(100.0, 100.0)

(100.0, 100.0)

...

How can I print the real position during the animation?

Thanks.

Tickler

What are you trying to achieve? If you want to add the circle to the center of your view, you can do this circle.center = self.view.center – Meek

I would like to know what is the exact position (CGPoint) of my circle during the animation. If I print the circle.center postion to the console, it will show just the start (0.0) and the end position (100,100). – Tickler

Answer 1

I figured out a possible answer.

CALayer has a presentation() function

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

the presentation layer has a frame property what is a CGRect and from here easy the calculate the midpoint.

Demo

Code

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()
    }
}

The idea came from here UIView animation determine center during animation

If you have some simpler or nicer solution, please add below. Thanks!

Tickler