Self-sizing UICollectionView cells

ViewControllerParent.swift

import UIKit

class ViewController: UIViewController {

    // CollectionView from Storyboard
    @IBOutlet weak var myCollectionView: UICollectionView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        myCollectionView.delegate = self
        myCollectionView.dataSource = self
        
        // Register the Xib for cell
        let nib = UINib(nibName: "myCustomCell", bundle: nil) 
        myCollectionView.register(nib, forCellWithReuseIdentifier: "reuseId")
        
        // IMPORTANT: this is the key to make your cells auto-sizing
        if let collectionViewLayout = myCollectionView.collectionViewLayout as? UICollectionViewFlowLayout {
            collectionViewLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
        }
    }

}