snapBehavior.swift

class ViewController: UIViewController {
    
    @IBOutlet private weak var cardView: UIView!
    
    private var animator: UIDynamicAnimator!
    
    private var snapping: UISnapBehavior!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        animator = UIDynamicAnimator(referenceView: view)
        snapping = UISnapBehavior(item: cardView, snapTo: view.center)
        animator.addBehavior(snapping)
        
        let panGesture = UIPanGestureRecognizer(target: self, action: #selector(pannedView))
        cardView.addGestureRecognizer(panGesture)
        cardView.isUserInteractionEnabled = true
        
    }
    
    
    @objc func pannedView(recognizer: UIPanGestureRecognizer) {
        
        switch recognizer.state {
            
        case .began:
            animator.removeBehavior(snapping)
            
        case .changed:
            let translation = recognizer.translation(in: view)
            cardView.center = CGPoint(x: cardView.center.x + translation.x, y: cardView.center.y + translation.y)
            recognizer.setTranslation(.zero, in: view)
        
        case .ended, .cancelled, .failed:
            animator.addBehavior(snapping)
        case .possible:
            break
        }
        
    }
}