Swift：移动后恢复UIView中心

Question

I'm using gestures to zoom and move a UIImageView (like Instagram zoom, for example). When the gesture ends, I want to restore UIImageView initial position, but I cannot get a copy of the initial center because it's a reference type. Using:

let prevCenter = myImage.center

is of course useless. How can I copy it?

Answer 1

On zoom and move apply transform to view. On the end just set .identity value.

Edit

Example:

@IBOutlet weak var butt: UIButton!

var offsetTransform: CGAffineTransform = .identity
var zoomTransform: CGAffineTransform = .identity

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.

    let pan = UIPanGestureRecognizer(target: self, action: #selector(onPan(pan:)))
    pan.minimumNumberOfTouches = 2
    pan.delegate = self
    view.addGestureRecognizer(pan)

    let pinch = UIPinchGestureRecognizer(target: self, action: #selector(onPinch(pinch:)))
    pinch.delegate = self
    view.addGestureRecognizer(pinch)
}

@objc func onPinch(pinch: UIPinchGestureRecognizer) {
    let s = pinch.scale
    zoomTransform = CGAffineTransform(scaleX: s, y: s)
    butt.transform = offsetTransform.concatenating(zoomTransform)
    if (pinch.state == .ended) {
        finish()
    }
}

@objc func onPan(pan: UIPanGestureRecognizer) {
    let t = pan.translation(in: view)
    offsetTransform = CGAffineTransform(translationX: t.x, y: t.y)
}

func updatePos() {
    butt.transform = offsetTransform.concatenating(zoomTransform)
}

func finish() {
    butt.transform = .identity
}

func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
    return true
}

Answer 2

Are you sure that you are not updating the prevCenter somewhere else? center is struct so you shouldn't have problems copying it.

Just make sure to take it (the center) when the view is in original state, before starting to zoom it and after it is drawn with correct frame

let imageView = UIImageView(frame: CGRect(x: 10, y: 10, width: 20, height: 20))

let prevCenter = view.center // 20, 20

imageView.center = CGPoint(x: 50, y: 50)

// imageView.center - 50, 50
// prevCenter - 20, 20

imageView.frame = CGRect(x: 40, y: 40, width: 10, height: 10)
// imageView.center - 45, 45
// prevCenter - 20, 20