View controller to get stuff moving around on screen :D Demo video: https://lookback.io/watch/TouJLFvYCs9Kyd9XC

GFStuffMovingAroundViewController.swift

//
//  GFStuffMovingAroundViewController.swift
//  GFTest
//
//  Created by Nevyn Bengtsson on 2015-09-10.
//  Copyright © 2015 Lookback AB. All rights reserved.
//

import UIKit

class GFStuffMovingAroundViewController: GFAppViewController {
	@IBOutlet var stuff: [UIView]!
	var animator: UIDynamicAnimator!
	var timer: NSTimer?
	var dynamic : UIDynamicItemBehavior!

    override func viewDidLoad() {
        super.viewDidLoad()
		
		animator = UIDynamicAnimator(referenceView: self.view)
		
		let collision = UICollisionBehavior(items: stuff)
		collision.translatesReferenceBoundsIntoBoundary = true
		animator.addBehavior(collision)
		
		dynamic = UIDynamicItemBehavior(items: stuff)
		self.animator.addBehavior(dynamic);
    }
	
	override func viewDidAppear(animated: Bool) {
		super.viewDidAppear(animated)
		timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: "moveSomething", userInfo: nil, repeats: true)
	}
	override func viewDidDisappear(animated: Bool) {
		super.viewDidDisappear(animated)
		timer?.invalidate()
		timer = nil
	}
	@objc func moveSomething() {
		dynamic.addLinearVelocity(
			CGPointMake(
				CGFloat(Int(arc4random_uniform(600))-300) + 100,
				CGFloat(Int(arc4random_uniform(600))-300) + 100
			),
			forItem: stuff[Int(arc4random_uniform(UInt32(stuff.count)))]
		)
	}
}