问题
I am trying to make a timeline where each section is a day and each day has many items (records). Here is my section (day) class:
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
}
}
}
}
As you can see I am adding year month and day attributes to my sections and using them to make each one "washable" so hopefully there will be only 1 section for each day at most.
Here is my 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)
}
}
But I get this crash error:
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'request for number of items in section 0 when there are only 0 sections in the collection view'
If I look at data, I can see that all of it is being populated correctly and when I print out snapshot.sectionIdentifiers it gives me all of those YearMonthDay objects. But somehow the dataSource is seeing 0 sections?
I think for a normal data source, I would just implement the delegate method - numberOfSections but since this is a diffable data source Im not sure what to do...
Edit:
data from the delegate is a dictionary of this type: [YearMonthDay:[TestRecord]]. Here is what it looks like when printed out
▿ 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
回答1:
I'm not super familiar with this new way of constructing a collectionView, but I believe the problem could be due to this line of code
snapshot.appendSections([ymd])
Why are you passing in an array here, for each iteration in the For loop? This should be done once, should it not?
for (ymd,records) in data {
snapshot.appendSections([ymd])
snapshot.appendItems(records,toSection: ymd)
}
to
snapshot.appendSections(Array(data.keys))
for (ymd,records) in data {
snapshot.appendItems(records,toSection: ymd)
}
来源：https://stackoverflow.com/questions/64509408/uicollectionviewdiffabledatasource-request-for-number-of-items-in-section-0-whe