4.iOS 14 - Lists in UICollection

在 iOS 14 中 UICollectionView 的功能得以继续增强，可以在一定程度上替换 UITableView。本文以一个案例的形式看看如何使用。学习之前需要进行说明：

1. 本文依然使用 “iOS 13 - DiffableDataSource” 一文中的数据。

2. 需要熟悉 DiffableDataSource 的基本使用。

创建UICollectionView

为 UICollectionView 配置 List 式的布局，还可以配置滑动菜单。

extension ViewController {
    // 创建列表式UICollectionView
    func makeCollectionView() -> UICollectionView {
        var config = UICollectionLayoutListConfiguration(appearance: .insetGrouped)
        // 右侧滑动删除
        config.trailingSwipeActionsConfigurationProvider = { indexPath in
            // 找到删除的内容
            guard let city = self.dataSource.itemIdentifier(for: indexPath) else { return nil }

            return UISwipeActionsConfiguration(
                actions: [UIContextualAction(
                    style: .destructive,
                    title: "Delete",
                    handler: { [weak self] _, _, completion in
                        // 调用删除数据
                        self?.deleteCity(city: city, indexPath: indexPath)
                        self?.updateList()

                        completion(true)
                    }
                )]
            )
        }

        // 左侧滑动添加
        config.leadingSwipeActionsConfigurationProvider = {  indexPath in
                   
            return UISwipeActionsConfiguration(
                actions: [UIContextualAction(
                    style: .normal,
                    title: "Add",
                    handler: { [weak self] _, _, completion in
                         // 调用增加数据
                        self?.addCity(city: City(name: "芜湖"), indexPath: indexPath)
                        self?.updateList()
                        
                        completion(true)
                    }
                )]
            )
        }

        // 列表布局
        let layout = UICollectionViewCompositionalLayout.list(using: config)
        
        return UICollectionView(frame: view.frame, collectionViewLayout: layout)
    }
}

增加与删除数据

extension ViewController {
    // 删除数据
    func deleteCity(city: City, indexPath: IndexPath) {
        if indexPath.section == 0 {
            firstCities.remove(at: firstCities.firstIndex(of: city)!)
        } else {
            secondCities.remove(at: secondCities.firstIndex(of: city)!)
        }
    }

    // 增加数据
    func addCity(city: City, indexPath: IndexPath) {
        if indexPath.section == 0 {
            firstCities.append(city)
        } else {
            secondCities.append(city)
        }
    }
}

注册Cell

在这里可以像 UITableView 一样，填充 Cell 的内容。

extension ViewController {
    // 注册Cell
    func makeCellRegistration() -> UICollectionView.CellRegistration<CityCollectionViewCell, City> {
        UICollectionView.CellRegistration { cell, _, city in
            // 自定义Cell显示的内容
            cell.cityLabel.text = city.name

            // AccessoryView
            cell.accessories = [.disclosureIndicator()]
        }
    }
}

DiffableDataSource

enum Section: CaseIterable {
    case first
    case second
}

extension ViewController {
    func updateList() {
        var snapshot = NSDiffableDataSourceSnapshot<Section, City>()
        // 添加两个分组
        snapshot.appendSections(Section.allCases)
        // 分别往两个分组添加数据
        snapshot.appendItems(firstCities, toSection: .first)
        snapshot.appendItems(secondCities, toSection: .second)
        dataSource.apply(snapshot)
    }
}

配置数据源

extension ViewController {
    // 配置数据源
    func makeDataSource() -> UICollectionViewDiffableDataSource<Section, City> {
        UICollectionViewDiffableDataSource<Section, City>(
            collectionView: collectionView,
            cellProvider: { view, indexPath, item in
                
                view.dequeueConfiguredReusableCell(
                    using: self.makeCellRegistration(),
                    for: indexPath,
                    item: item
                )
            }
        )
    }
}

ViewController

class ViewController: UIViewController {
    // 创建UICollectionView
    private lazy var collectionView = makeCollectionView()
    // 创建DataSource
    private lazy var dataSource = makeDataSource()

    let cityNames = ["北京", "南京", "西安", "杭州", "苏州"]
    // 第一组
    var firstCities: [City] = []
    // 第二组
    var secondCities: [City] = []

    override func viewDidLoad() {
        super.viewDidLoad()

        for name in cityNames {
            firstCities.append(City(name: name))
            secondCities.append(City(name: name))
        }

        // CollectionView关联DataSource
        collectionView.dataSource = dataSource

        view.addSubview(collectionView)

        // 第一次进来刷新
        updateList()
    }
}

效果