UIView animation determine center during animation

Question

I\'m using UIView\'s + animateWithDuration:delay:options:animations:completion: method to move my view along a line over the course of a few seconds or so.

Answer 1

I know its too late but maybe it can help somebody else.

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

The code in swift 3

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()
    }
}

Answer 2

UIViews are backed by CALayers, and it is the layer that does the actual animation. CALayer exposes a property presentationLayer which, when accessed, returns a copy of the CALayer that represents, as closely as it can, the current state visible to the user. By asking for the view.layer.presentationLayer.frame you can get the frame of the layer as visible to the user right now, and this corresponds to the frame of the UIView.