andresbrun

modalViewExitBehaviour = UIDynamicItemBehavior(items: [targetView])
// Action is called in every animation step
modalViewExitBehaviour.action = { [unowned self] _ in
    // Check if all views are outside of the reference frame
    if !self.allViews.contains(where: { $0.frame.intersects(self.superview.bounds) }) {
        self.onDismiss?()
    }
}
animator?.addBehavior(modalViewExitBehaviour)    
        

andresbrun

let pushBehaviour = UIPushBehavior(items: [mainModalView], mode: .instantaneous)
pushBehaviour.pushDirection = velocity.vector * Constants.pushForceRatio
pushBehaviour.setTargetOffsetFromCenter(offset, for: mainModalView)
animator.addBehavior(pushBehaviour)

animator.addBehavior(gravityBehaviour)

animator.removeBehaviors(itemsAttachmentBehaviours)

// Handy extension

andresbrun

class BallView: UIImageView {
    init(size: CGFloat) {
        super.init(frame: CGRect(origin: .zero, size: CGSize(width: size, height: size)))
        image = UIImage(named: "basketball-png-0")
        contentMode = .scaleToFill
        layer.cornerRadius = size * 0.5
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")

andresbrun

let dynamicBehaviour = UIDynamicItemBehavior(items: balls)
dynamicBehaviour.elasticity = 0.8
dynamicBehaviour.friction = 5.0
animator.addBehavior(dynamicBehaviour)

andresbrun

let slidingBehaviour = UIAttachmentBehavior.slidingAttachment(with: targetView, 
                                                              attachedTo: draggableView, 
                                                              attachmentAnchor: targetView.center, 
                                                              axisOfTranslation: CGVector(dx: 1, dy: 0))
animator.addBehavior(slidingBehaviour)

andresbrun

import UIKit
import XCPlayground

public class DynamicModalBehaviour: NSObject {
    private var animator: UIDynamicAnimator?
    private var dragAttachmentBehaviour: UIAttachmentBehavior!
    private var itemsCollisionBehaviour: UICollisionBehavior!
    private var modalViewExitBehaviour: UIDynamicItemBehavior!
    private var itemsAttachmentBehaviours: [UIAttachmentBehavior]!
    private var snapBehaviours: [UISnapBehavior]!

andresbrun

// Dragging an element with a PanGestureRecognizer for instance
let dragAttachmentBehaviour = UIAttachmentBehavior(item: targetView,
                                                   offsetFromCenter: offsetFromCenter,
                                                   attachedToAnchor: dragLocation)

// Attaching two box in a chain
let boxAttachmentBehaviour = UIAttachmentBehavior(item: box1, 
                                                  offsetFromCenter: UIOffset(horizontal: 0, vertical: box1.bounds.midY), 
                                                  attachedTo: box2, 
                                                  offsetFromCenter: UIOffset(horizontal: 0, vertical: -box2.bounds.midY))

andresbrun

let collisionBehaviour = UICollisionBehavior(items: [targetView])
animator.addBehavior(collisionBehaviour)

// Collision with bounds of superview
collisionBehaviour.setTranslatesReferenceBoundsIntoBoundary(with: .zero)

// Collision with custom boundaries
collisionBehaviour.addBoundary(withIdentifier: "barrier" as NSCopying, 
                               for: UIBezierPath(ovalIn: containerView.bounds))

andresbrun

let snapBehaviour = UISnapBehavior(item: targetView, snapTo: CGPoint(x: 100, y: 100))
animator.addBehavior(snapBehaviour)

// You can configure the oscillation of the item when it has to go to the snap point
snapBehaviour.damping = 0.5 // Medium oscillation 

andresbrun

let gravityBehaviour = UIGravityBehavior(items: [targetView])
animator.addBehavior(gravityBehaviour)

// It can be defined with
gravityBehaviour.magnitude = 1.0 // Gravity on earth
gravityBehaviour.angle = .pi / 2.0 // downward direction

// Or
gravityBehaviour.gravityDirection = CGVector(dx: 0.0, dy: 1.0) // Gravity on earth