Implement UIKitDynamics for dragging view off screen

Question

I\'m trying to figure out implement UIKit Dynamics that are similar to those in Jelly\'s app (specifically swiping down to drag view off-screen).

See the animation:

Answer 1

SWIFT 3.0 :

import UIKit

class SwipeToDisMissView: UIView {

var animator : UIDynamicAnimator?

func initSwipeToDismissView(_ parentView:UIView)  {
    let panGesture = UIPanGestureRecognizer(target: self, action: #selector(SwipeToDisMissView.panGesture))
    self.addGestureRecognizer(panGesture)
    animator = UIDynamicAnimator(referenceView: parentView)
}

func panGesture(_ gesture:UIPanGestureRecognizer)  {
    var attachment : UIAttachmentBehavior?
    var lastTime = CFAbsoluteTime()
    var lastAngle: CGFloat = 0.0
    var angularVelocity: CGFloat = 0.0

    if gesture.state == .began {
        self.animator?.removeAllBehaviors()
        if let gestureView = gesture.view {
            let pointWithinAnimatedView = gesture.location(in: gestureView)
            let offset = UIOffsetMake(pointWithinAnimatedView.x - gestureView.bounds.size.width / 2.0, pointWithinAnimatedView.y - gestureView.bounds.size.height / 2.0)
            let anchor = gesture.location(in: gestureView.superview!)
            // create attachment behavior
            attachment = UIAttachmentBehavior(item: gestureView, offsetFromCenter: offset, attachedToAnchor: anchor)
            // code to calculate angular velocity (seems curious that I have to calculate this myself, but I can if I have to)
            lastTime = CFAbsoluteTimeGetCurrent()
            lastAngle = self.angleOf(gestureView)
            weak var weakSelf = self
            attachment?.action = {() -> Void in
                let time = CFAbsoluteTimeGetCurrent()
                let angle: CGFloat = weakSelf!.angleOf(gestureView)
                if time > lastTime {
                    angularVelocity = (angle - lastAngle) / CGFloat(time - lastTime)
                    lastTime = time
                    lastAngle = angle
                }
            }
            self.animator?.addBehavior(attachment!)
        }
    }
    else if gesture.state == .changed {
        if let gestureView = gesture.view {
            if let superView = gestureView.superview {
                let anchor = gesture.location(in: superView)
                if let attachment = attachment {
                    attachment.anchorPoint = anchor
                }
            }
        }
    }
    else if gesture.state == .ended {
        if let gestureView = gesture.view {
            let anchor = gesture.location(in: gestureView.superview!)
            attachment?.anchorPoint = anchor
            self.animator?.removeAllBehaviors()
            let velocity = gesture.velocity(in: gestureView.superview!)
            let dynamic = UIDynamicItemBehavior(items: [gestureView])
            dynamic.addLinearVelocity(velocity, for: gestureView)
            dynamic.addAngularVelocity(angularVelocity, for: gestureView)
            dynamic.angularResistance = 1.25
            // when the view no longer intersects with its superview, go ahead and remove it
            weak var weakSelf = self
            dynamic.action = {() -> Void in
                if !gestureView.superview!.bounds.intersects(gestureView.frame) {
                    weakSelf?.animator?.removeAllBehaviors()
                    gesture.view?.removeFromSuperview()
                }
            }
            self.animator?.addBehavior(dynamic)

            let gravity = UIGravityBehavior(items: [gestureView])
            gravity.magnitude = 0.7
            self.animator?.addBehavior(gravity)
        }
    }
}

func angleOf(_ view: UIView) -> CGFloat {
    return atan2(view.transform.b, view.transform.a)
}
}