IGListKit/Examples/Examples-iOS/IGListKitExamples/ViewControllers/CompositionLayoutViewController.swift

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

import IGListKit
import UIKit

/// Enables SectionControllers to return their own layout. In the future, we might want IGListKit
/// to handle this, but for now, lets keep it simple.
protocol CompositionLayoutCapable {
    func collectionViewSectionLayout(layoutEnvironment: NSCollectionLayoutEnvironment) -> NSCollectionLayoutSection?
}

/// Like MixedDataViewController, but using UICollectionViewCompositionalLayout
final class CompositionLayoutViewController: UIViewController, ListAdapterDataSource {
    
    private var collectionView: UICollectionView?
    
    private lazy var adapter: ListAdapter = {
        return ListAdapter(updater: ListAdapterUpdater(), viewController: self)
    }()
    
    private let data: [Any] = [
        "Maecenas faucibus mollis interdum. Duis mollis, est non commodo luctus, nisi erat porttitor ligula, eget lacinia odio sem nec elit.",
        "Praesent commodo cursus magna, vel scelerisque nisl consectetur et.",
        "Nullam quis risus eget urna mollis ornare vel eu leo. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.",
        "Fusce dapibus, tellus ac cursus commodo, tortor mauris condimentum nibh, ut fermentum massa justo sit amet risus.",
    ]
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Layout
        let layout = UICollectionViewCompositionalLayout {[weak self] (sectionIndex: Int, layoutEnvironment: NSCollectionLayoutEnvironment) -> NSCollectionLayoutSection? in
            guard let self = self else {
                return nil
            }
            let controller = self.adapter.sectionController(forSection: sectionIndex)
            guard let controller = controller as? CompositionLayoutCapable else {
                return nil
            }
            return controller.collectionViewSectionLayout(layoutEnvironment: layoutEnvironment)
        }
        
        // Collection View
        let collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
        self.collectionView = collectionView
        view.addSubview(collectionView)
        adapter.collectionView = collectionView
        adapter.dataSource = self
    }
    
    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        collectionView?.frame = view.bounds
    }
    
    // MARK: ListAdapterDataSource
    
    func objects(for listAdapter: ListAdapter) -> [ListDiffable] {
        return data.map { $0 as! ListDiffable }
    }
    
    func listAdapter(_ listAdapter: ListAdapter, sectionControllerFor object: Any) -> ListSectionController {
        switch object {
        case is String:
            return ExpandableComposableSectionController()
        default:
            return ListSectionController()
        }
    }
    
    func emptyView(for listAdapter: ListAdapter) -> UIView? { return nil }
    
}