Swift 中具有不同单元格类型的可重用数据源

Question

基于此 article 我为 UICollectionView 创建了一个可重用的数据源，如下所示：-

final class CollectionViewDataSource<Model>: NSObject, UICollectionViewDataSource {
  typealias CellConfigurator = (Model, UICollectionViewCell) -> Void
  var models: [Model] = []

  private let reuseIdentifier: String
  private let cellConfigurator: CellConfigurator

  init(reuseIdentifier: String, cellConfigurator: @escaping CellConfigurator) {
    self.reuseIdentifier = reuseIdentifier
    self.cellConfigurator = cellConfigurator
  }

  func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return models.count
  }

  func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let model = models[indexPath.item]
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath)
    cellConfigurator(model, cell)
    return cell
  }
}

然后我扩展了这个 class 所以我可以提供 'cell specific' 基于模型类型的设置

extension CollectionViewDataSource where Model == HomeFeedItem {
  static func make(reuseIdentifier: String = "FEED_ARTICLE_CELL") -> CollectionViewDataSource {
    return CollectionViewDataSource(reuseIdentifier: reuseIdentifier, cellConfigurator: { item, cell in
      (cell as? FeedArticleCell)?.render(with: item)
    })
  }
}

extension CollectionViewDataSource where Model == HomeFeedAlertItem {
  static func make(reuseIdentifier: String = "FEED_ALERT_CELL") -> CollectionViewDataSource {
    return CollectionViewDataSource(reuseIdentifier: reuseIdentifier, cellConfigurator: { item, cell in
      (cell as? FeedAlertCell)?.render(with: item)
    })
  }
}

这是完美的，但是，这些单元格中的每一个都有不同的设计，但实际上接受非常相似的属性（其他单元格也是如此）-因此我正在考虑创建一个简单的 FeedItemModel 并在呈现我的提要之前映射这些属性。这将确保在我呈现提要项目的任何地方，我总是处理相同的属性。

考虑到这一点，我尝试创建类似的东西：-

extension CollectionViewDataSource where Model == FeedItemModel {
  static func make(reuseIdentifier: String = "FEED_ARTICLE_CELL") -> CollectionViewDataSource {
    return CollectionViewDataSource(reuseIdentifier: reuseIdentifier, cellConfigurator: { item, cell in
      switch item.type {
      case .news: (cell as? FeedArticleCell)?.render(with: item)
      case .alert: (cell as? FeedAlertCell)?.render(with: item)
      }
    })
  }
}

然而，如果 item.type 为 .alert，则 reuseIdentifier 字段不再正确，这会下降。

如何重构此模式以允许我对同一模型使用不同的单元格类型？或者我应该放弃这种方法并坚持为每种细胞类型使用不同的模型，而不管输入属性是否相同？

Answer 1

如何为单元格添加第二个泛型类型

final class CollectionViewDataSource<Model, CellType : UICollectionViewCell>: NSObject, UICollectionViewDataSource {
    typealias CellConfigurator = (Model, CellType) -> Void
    var models: [Model] = []

    private let reuseIdentifier: String
    private let cellConfigurator: CellConfigurator

    init(reuseIdentifier: String, cellConfigurator: @escaping CellConfigurator) {
        self.reuseIdentifier = reuseIdentifier
        self.cellConfigurator = cellConfigurator
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return models.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let model = models[indexPath.item]
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! CellType
        cellConfigurator(model, cell)
        return cell
    }
}

Answer 2

您可以在 FeedItemModelType

中添加关联标识符

var reuseIdentifier: String {
    switch self {
        case .news: return "NEW_CELL"
        case .alert: return "ALERT_CELL"
   }
}

你的工厂方法看起来像这样

extension CollectionViewDataSource where Model == FeedItemModel {
  static func make() -> CollectionViewDataSource {
    return CollectionViewDataSource(reuseIdentifier: item.type.reuseIdentifier, cellConfigurator: { item, cell in
      switch item.type {
      case .news: (cell as? FeedArticleCell)?.render(with: item)
      case .alert: (cell as? FeedAlertCell)?.render(with: item)
      }
    })
  }
}

Answer 3

您可以创建一个协议，例如

protocol FeedRenderable {
  var reuseIdentifier: String { get }
}

然后确保Model类型符合FeedRenderable.

然后您可以将 CollectionViewDataSource 重构为

final class CollectionViewDataSource<Model>: NSObject, UICollectionViewDataSource where Model: FeedRenderable {
  typealias CellConfigurator = (Model, UICollectionViewCell) -> Void
  var models: [Model] = []

  private let cellConfigurator: CellConfigurator

  init(_ cellConfigurator: @escaping CellConfigurator) {
    self.cellConfigurator = cellConfigurator
  }

  func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return models.count
  }

  func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let model = models[indexPath.item]
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: model.reuseIdentifier, for: indexPath)
    cellConfigurator(model, cell)
    return cell
  }
}

注意以下变化

final class CollectionViewDataSource<Model>: NSObject, UICollectionViewDataSource where Model: FeedRenderable {
....
init(_ cellConfigurator: @escaping CellConfigurator) 
....
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: model.reuseIdentifier, for: indexPath)
....

然后您可以确保传入的任何模型都根据 item.type 属性

设置其 reuseIdentifier

extension GenericFeedItem: FeedRenderable {
  var reuseIdentifier: String {
    switch type {
    case .news: return "FEED_ARTICLE_CELL"
    case .alert: return "FEED_ALERT_CELL"
    }
  }
}

您的分机将变为

extension CollectionViewDataSource where Model == GenericFeedItem {
  static func make() -> CollectionViewDataSource {
    return CollectionViewDataSource() { item, cell in
      (cell as? FeedArticleCell)?.render(with: item)
      (cell as? FeedAlertCell)?.render(with: item)
    }
  }
}

Swift 中具有不同单元格类型的可重用数据源

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