UICollectionViewCompositionalLayout

UICollectionViewCompositionalLayout.swift

import UIKit

final class HomeViewController: UIViewController {
    private typealias DataSource = UICollectionViewDiffableDataSource<Int, String>
    private typealias Snapshot = NSDiffableDataSourceSnapshot<Int, String>

    private lazy var dataSource: DataSource = {
        let cellHandler = UICollectionView.CellRegistration { (cell: UICollectionViewListCell, indexPath: IndexPath, itemIdentifier: String) in
            var config = cell.defaultContentConfiguration()
            config.text = itemIdentifier
            cell.contentConfiguration = config
        }

        let dataSource = DataSource(collectionView: collectionView) { collectionView, indexPath, itemIdentifier in
            collectionView.dequeueConfiguredReusableCell(using: cellHandler, for: indexPath, item: itemIdentifier)
        }

        return dataSource
    }()

    private lazy var collectionView: UICollectionView = {
        let collectionView = UICollectionView(frame: .zero, collectionViewLayout: makeCollectionViewLayout())
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        collectionView.register(UICollectionViewListCell.self, forCellWithReuseIdentifier: "Cell")
        return collectionView
    }()

    private func makeCollectionViewLayout() -> UICollectionViewCompositionalLayout {
        UICollectionViewCompositionalLayout { section, environment in
            let itemLayout = NSCollectionLayoutItem(
                layoutSize: .init(widthDimension: .fractionalWidth(0.5), heightDimension: .estimated(200))
            )

            let groupLayout: NSCollectionLayoutGroup = .horizontal(
                layoutSize: .init(widthDimension: .fractionalWidth(1), heightDimension: .estimated(200)),
                subitems: [itemLayout]
            )

            let sectionLayout = NSCollectionLayoutSection(group: groupLayout)

            return sectionLayout
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .systemBackground
        view.addSubview(collectionView)

        NSLayoutConstraint.activate([
            collectionView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
            collectionView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
            collectionView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor),
            collectionView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor)
        ])

        var snapshot = Snapshot()
        snapshot.appendSections([0])
        snapshot.appendItems(["1d ad sad sds dsad s dssad sfdf dsdddfsf df dsfsdf sfsd","2","3","4","5","6"])

        dataSource.apply(snapshot)

        collectionView.dataSource = dataSource
    }
}