<code>

@IBOutlet weak var image1: UIImageView!
@IBOutlet weak var image2: UIImageView!
@IBOutlet weak var target1: UIImageView!
@IBOutlet weak var target2: UIImageView!

var target1flg: Bool!
var target2flg: Bool!

var imageViewOrigin: CGPoint!

override func viewDidLoad() {
    super.viewDidLoad()

    target1flg = true
    target2flg = true

    addPanGesture(v: image1)
    addPanGesture(v: image2)

}

func addPanGesture(v: UIView) {

    let pan = UIPanGestureRecognizer(target: self, action: #selector(sample.handlePan(sender:)))
    v.addGestureRecognizer(pan)
}

@objc func handlePan(sender: UIPanGestureRecognizer) {

    let pannedImageView = sender.view!

    switch sender.state {

    case .began:

        imageViewOrigin = pannedImageView.frame.origin
        view.bringSubview(toFront: pannedImageView)

    case .changed:

        moveViewWithPan(v: pannedImageView, sender: sender)

    case .ended:
        if pannedImageView.frame.intersects(target1.frame) && target1flg == true {
            snapView(v: pannedImageView, targetBox: target1)
            target1flg = false

        }
        else if pannedImageView.frame.intersects(target2.frame) && target2flg == true  {
            snapView(v: pannedImageView, targetBox: target2)
            target2flg = false

        }
        else {
            returnViewToOrigin(v: pannedImageView, loc: imageViewOrigin)
        }

    default:
        break
    }
}


func moveViewWithPan(v: UIView, sender: UIPanGestureRecognizer) {

    let translation = sender.translation(in: view)

    v.center = CGPoint(x: v.center.x + translation.x, y: v.center.y + translation.y)
    sender.setTranslation(CGPoint.zero, in: view)
}


func returnViewToOrigin(v: UIView, loc: CGPoint) {

    UIView.animate(withDuration: 0.3, animations: {
        v.frame.origin = loc
    })
}

func snapView(v:UIView, targetBox:UIImageView){
    UIView.animate(withDuration: 0.3) {

        v.center = CGPoint(x:targetBox.center.x, y: targetBox.center.y)
        v.isUserInteractionEnabled = false
    }
}