ViewController.swift

init(){
    let layout = UICollectionViewCompositionalLayout { (section, env) -> NSCollectionLayoutSection? in
        // 1
        let item = NSCollectionLayoutItem(layoutSize: .init(widthDimension: .fractionalWidth(1.0), heightDimension: .absolute(200)))
        // 2
        let group = NSCollectionLayoutGroup.horizontal(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0), heightDimension: .absolute(200)), subitems: [item])
        // 3
        let section = NSCollectionLayoutSection(group: group)
        return section
    }
    super.init(collectionViewLayout: layout)
}