Observation #1: Faces are falling from the sky!

Observation1.swift

import UIKit

class ViewController: UIViewController {

    // MARK: Public
    
    @IBOutlet weak var bottomView: UIView!
  
    // MARK: Private
  
     // 1: the class that will allow us to manage our behaviors aka specific dynamic behavior
    private lazy var animator = UIDynamicAnimator(referenceView: self.view)
    
    // MARK: Lifecycle

    override func viewDidLoad() {
        super.viewDidLoad()

        let faces: [UIImage] = [
            #imageLiteral(resourceName: "aymen5"),#imageLiteral(resourceName: "aymen3"),#imageLiteral(resourceName: "aymen1"),#imageLiteral(resourceName: "aymen2"),#imageLiteral(resourceName: "aymen7"),#imageLiteral(resourceName: "aymen6"),#imageLiteral(resourceName: "aymen4"),#imageLiteral(resourceName: "aymen10"),#imageLiteral(resourceName: "aymen8"),#imageLiteral(resourceName: "aymen9")
        ]

        let gravityBehavior = UIGravityBehavior(items: [])

        for (index, face) in faces.enumerated() {

            // 2: We delay the creation of the face view to display them "one by one"
            DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(index*150)) {

                // 3: Faces will have a random size
                let size: CGFloat = CGFloat([50.0, 65.0, 80.0, 100.0].randomElement()!)


                // 4
                // x: We positionnate the face randomly in the x-axis, so that faces can fall down from different position
                // y: negative so that they are falling from above
                let bubbleView = FaceView(
                    frame: .init(
                        x: CGFloat.random(in: 0...UIScreen.main.bounds.width-size),
                        y: -50,
                        width: size,
                        height: size
                    ),
                    image: face
                )

                self.view.addSubview(bubbleView)

                // 5: We add a gravity behavior for each of our face
                gravityBehavior.addItem(bubbleView)
            }
        }

        // 6: We ask our "manager" to add the gravity behavior, which will automatically trigger the animation.
        animator.addBehavior(gravityBehavior)
    }
}