UICollectionViewDiffableDataSource：当collection view只有0个section时，请求section 0的item数

Question

我正在尝试制作一个时间表，其中每个部分都是一天，并且每一天都有许多项目（记录）。 这是我的部分（日）课：

class YearMonthDay: Comparable, Hashable {
    let year: Int
    let month: Int
    let day: Int
    
    init(year: Int, month: Int, day: Int) {
        self.year = year
        self.month = month
        self.day = day
    }

    init(date: Date) {
        let comps = Calendar.current.dateComponents([.year, .month, .day], from: date)
        self.year = comps.year!
        self.month = comps.month!
        self.day = comps.day!
    }
    func hash(into hasher: inout Hasher) {
        hasher.combine(year)
        hasher.combine(month)
        hasher.combine(day)
    }
    
    var date: Date {
        var dateComponents = DateComponents()
        dateComponents.year = year
        dateComponents.month = month
        dateComponents.day = day
        return Calendar.current.date(from: dateComponents)!
    }

    static func == (lhs: YearMonthDay, rhs: YearMonthDay) -> Bool {
        return lhs.year == rhs.year && lhs.month == rhs.month && lhs.day == rhs.day
    }

    static func < (lhs: YearMonthDay, rhs: YearMonthDay) -> Bool {
        if lhs.year != rhs.year {
            return lhs.year < rhs.year
        } else {
            if lhs.month != rhs.month {
                return lhs.month < rhs.month
            } else {
                return lhs.day < rhs.day
            }
        }
    }
}

如您所见，我正在向我的部分添加年月日属性，并使用它们使每个部分都“可清洗”，因此希望每天最多只有 1 个部分。

这是我的 collectionViewController...

class TimelineViewController: UICollectionViewController {

    private lazy var dataSource = makeDataSource()
    
    fileprivate typealias DataSource = UICollectionViewDiffableDataSource<YearMonthDay,TestRecord>
    fileprivate typealias DataSourceSnapshot = NSDiffableDataSourceSnapshot<YearMonthDay,TestRecord>
    
    public var data: [YearMonthDay:[TestRecord]] = [:]
    var delegate: TimelineViewControllerDelegate?
    override func viewDidLoad() {
        super.viewDidLoad()
        guard let data = delegate?.dataForTimelineView() else { return }
        self.data = data
        collectionView.showsHorizontalScrollIndicator = true
        configureHierarchy()
        configureDataSource()
        applySnapshot()
        
    }
}
extension TimelineViewController {
    fileprivate func makeDataSource() -> DataSource {
        let dataSource = DataSource(
            collectionView: collectionView,
            cellProvider: { (collectionView, indexPath, testRecord) ->
              UICollectionViewCell? in
                let cell = collectionView.dequeueReusableCell(withReuseIdentifier: TimelineDayCell.identifier, for: indexPath) as? TimelineDayCell
                cell?.configure(with: testRecord)
                cell?.dayLabel.text = String(indexPath.section)+","+String(indexPath.row)
                return cell
            })
        return dataSource
    }
    func configureDataSource() {
        self.collectionView!.register(TimelineDayCell.nib, forCellWithReuseIdentifier: TimelineDayCell.identifier)
    }
    func applySnapshot(animatingDifferences: Bool = true) {
      // 2
      var snapshot = DataSourceSnapshot()
      for (ymd,records) in data {
          snapshot.appendSections([ymd])
          snapshot.appendItems(records,toSection: ymd)
      }
      // This is where the error occurs. 
      dataSource.apply(snapshot, animatingDifferences: animatingDifferences)
    }
}

但我收到此崩溃错误：

*** 由于未捕获的异常“NSInternalInconsistencyException”而终止应用程序，原因：“当集合视图中只有 0 个部分时，请求第 0 部分中的项目数”

如果我查看数据，我可以看到所有数据都已正确填充，当我打印出 snapshot.sectionIdentifiers 时，它会为我提供所有这些 YearMonthDay 对象。但不知何故，数据源看到了 0 个部分？

我认为对于普通数据源，我只会实现委托方法 - numberOfSections 但由于这是一个可区分的数据源，我不知道该怎么做...

编辑：

来自委托的数据是这种类型的字典：[YearMonthDay:[TestRecord]]。这是打印出来的样子

▿ 7 elements
  ▿ 0 : 2 elements
    ▿ key : <YearMonthDay: 0x600000e880f0>
    ▿ value : 1 element
      ▿ 0 : TestRecord
        - identifier : 5D05C73D-8863-47E3-B1E5-3331791A3FB8
        - type : SweatNetOffline.RecordType
        - progression : 1
        ▿ timeStamp : 2020-10-16 04:56:59 +0000
          - timeIntervalSinceReferenceDate : 624517019.639298
  ▿ 1 : 2 elements
    ▿ key : <YearMonthDay: 0x600000e89ec0>
    ▿ value : 1 element
      ▿ 0 : TestRecord
        - identifier : C40F5884-AABF-43C8-9921-95DD1423AC4D
        - type : SweatNetOffline.RecordType
        - progression : 1
        ▿ timeStamp : 2020-10-22 04:56:59 +0000
          - timeIntervalSinceReferenceDate : 625035419.639274
  ▿ 2 : 2 elements
    ▿ key : <YearMonthDay: 0x600000e88cf0>
    ▿ value : 1 element
      ▿ 0 : TestRecord
        - identifier : 5EE70ABF-4C4D-4FB5-A850-3D0081D91D0D
        - type : SweatNetOffline.RecordType
        - progression : 2
        ▿ timeStamp : 2020-10-20 04:56:59 +0000
          - timeIntervalSinceReferenceDate : 624862619.639284
  ▿ 3 : 2 elements
    ▿ key : <YearMonthDay: 0x600000e8a0a0>
    ▿ value : 1 element
      ▿ 0 : TestRecord
        - identifier : 59152DCA-63EC-4EBF-ACDB-B45FA5E85EED
        - type : SweatNetOffline.RecordType
        - progression : 2
        ▿ timeStamp : 2020-10-18 04:56:59 +0000
          - timeIntervalSinceReferenceDate : 624689819.639291
  ▿ 4 : 2 elements
    ▿ key : <YearMonthDay: 0x600000e89890>
    ▿ value : 1 element
      ▿ 0 : TestRecord
        - identifier : 0E12D3D6-0650-41A6-AC12-EB75EFA0A151
        - type : SweatNetOffline.RecordType
        - progression : 0
        ▿ timeStamp : 2020-10-26 04:56:59 +0000
          - timeIntervalSinceReferenceDate : 625381019.638627
  ▿ 5 : 2 elements
    ▿ key : <YearMonthDay: 0x600000e89e60>
    ▿ value : 1 element
      ▿ 0 : TestRecord
        - identifier : 99A929C4-B94B-4F8F-8C6D-2C356D778D95
        - type : SweatNetOffline.RecordType
        - progression : 2
        ▿ timeStamp : 2020-10-24 04:56:59 +0000
          - timeIntervalSinceReferenceDate : 625208219.639251
  ▿ 6 : 2 elements
    ▿ key : <YearMonthDay: 0x600000e89f20>
    ▿ value : 1 element
      ▿ 0 : TestRecord
        - identifier : EF6EB971-504B-4587-8038-FB8C3FD7ACDC
        - type : SweatNetOffline.RecordType
        - progression : 1
        ▿ timeStamp : 2020-10-14 04:56:59 +0000
          - timeIntervalSinceReferenceDate : 624344219.639307

Answer 1

我对这种构建collectionView的新方法不是很熟悉，但我相信问题可能出在这行代码

snapshot.appendSections([ymd])

为什么要在此处为​​ For 循环中的每次迭代传入一个数组？这应该做一次，不是吗？

for (ymd,records) in data {
      snapshot.appendSections([ymd])
      snapshot.appendItems(records,toSection: ymd)
}

到

snapshot.appendSections(Array(data.keys))
for (ymd,records) in data {
      snapshot.appendItems(records,toSection: ymd)
  }