Adding Inertia to a UIView Pan with UIDynamicBehavior

Question

I am trying to pan 'blockView' with UIPanGestureRecognizer. When the pan is 'Ended', want the 'blockView' to decelerate with inertia, just as a UIScrollView would end scrolling with inertia.

override func viewDidLoad() {
    super.viewDidLoad()
    self.dynamicAnimator = UIDynamicAnimator(referenceView: self.view)

    let collider = UICollisionBehavior(items: [self.magnifiedView!])
    collider.collisionDelegate = self
    collider.collisionMode = .Boundaries
    collider.translatesReferenceBoundsIntoBoundary = true
    self.dynamicAnimator.addBehavior(collider)

    self.dynamicProperties = UIDynamicItemBehavior(items: [self.magnifiedView!])
    //self.dynamicProperties.elasticity = 1.0
    //self.dynamicProperties.friction = 0.0
    self.dynamicProperties.allowsRotation = false
    //self.dynamicProperties.resistance = 10.0
    self.dynamicAnimator.addBehavior(self.dynamicProperties)

}


func panBlockView (panGesture: UIPanGestureRecognizer) {
    switch panGesture {
    case .Began:
        self.blockViewLocation = (self.blockView.center)!
    case .Changed:
        let translation = panGesture.translationInView(self.view)
        self.blockView.center = CGPointMake(self.blockViewLocation.x + translation.x, self.self.blockViewLocation.y + translation.y)
    case .Ended, .Cancelled:
        self.dynamicAnimator.addLinearVelocity(panGesture.velocityInView(self.view), forItem: self.blockView)
    }
}

Issue: As I pan the view, 'blockView' tries to snap to the origin where the pan was originated from. When the pan 'Ends', it creates inertia, but it starts from the origin of the pan (after snapping to pan origin).

NOTE: Above code works without issues just to PAN THE VIEW.

Answer 1

Adding a Snap Behavior and have it snap fixed the issue.