Ios 在SwiftData中从@ Query创建可排序、有序和分组的数据

我一直在try 构建的SwiftUI应用程序的排序和分组过程.

我看到的所有教程在排序和过滤方面都相当"基础"，特别是在使用SwiftData时.

我想要整合的不仅是按其中一个属性和正向/反向排序，而且还将数据分组.

例如，这是Apple的Earthquake项目的代码(为了简洁起见，删除了一些项目):

struct QuakeList: View {
    @Environment(ViewModel.self) private var viewModel
    @Environment(\.modelContext) private var modelContext
    @Query private var quakes: [Quake]

    init(
        sortParameter: SortParameter = .time,
        sortOrder: SortOrder = .reverse
    ) {
        switch sortParameter {
            case .time:
                _quakes = Query(sort: \.time, order: sortOrder)
            case .magnitude:
                _quakes = Query(sort: \.magnitude, order: sortOrder)
        }
    }

他们在这里所做的是将sortParameter和sortOrder传递给这个视图，并在更改/更新时重新呈现视图.

我如何扩展它，使它也可以处理分组，使quakes变量实际上是一个多维数组，甚至是一个字典.

例如，我试图这样做来执行渲染:

enum GroupOption { // New grouping for Section
    case time
    case magnitude
    case none
}

struct ListScreen: View {
    @Environment(ViewModel.self) private var viewModel
    @Environment(\.modelContext) private var modelContext
    @Query private var quakes: [Quake]
    @State private var groupedQuakes: [[Quake]] = [] // New multidimensional array

    init(
        sortParameter: SortParameter = .time,
        sortOrder: ComparisonResult = .orderedAscending, // using ComparisonResult to store the enum value in defaults
        sortGrouping: GroupOption = .none
    ) {
        switch (sortParameter, sortOrder) {
            case (.time, .orderedAscending):
                _quakes = Query(sort: \.time, order: .forward)
            case (.time, .orderedDescending):
                _quakes = Query(sort: \.time, order: .reverse)

            case (.magnitude, .orderedAscending):
                _quakes = Query(sort: \.magnitude, order: .forward)
            case (.magnitude, .orderedDescending):
                _quakes = Query(sort: \.magnitude, order: .reverse)

            default:
                _quakes = Query(sort: \.time, order: .forward)
        }

        switch sortGrouping {
            case .time:
                groupedQuakes = Dictionary(grouping: _quakes.wrappedValue, by: { $0.time })
                    .sorted(by: { $0.key < $1.key })
                    .map({ $0.value })
            case .magnitude:
                groupedQuakes = Dictionary(grouping: _quakes.wrappedValue, by: { $0.magnitude })
                    .sorted(by: { $0.key < $1.key })
                    .map({ $0.value })
            case .none:
                groupedQuakes = [_quakes.wrappedValue]
        }
    }

但是，当我在视图主体中使用它时，它是空的.因此，从// 1切换到// 2会使数据数组返回空.

// 1
List(quakes) { quake in
  QuakeRow(quake: quake)
}

// 2
List {
  ForEach(groupedQuakes, id: \.self) { group in
    Section {
      ForEach(group) { quake in
        QuakeRow(quake: quake)
      }
    } header: {
      groupHeader(for: group)
    }
  }
}
// ...
func groupHeader(for group: [Quake]) -> Text {
  guard let group = group.first else { return Text("Unknown") }
  switch groupOption {
    case .time:
      return Text(group.time.formatted(date: .numeric, time: .omitted))
    case .magnitude:
      return Text("\(group.magnitude)")
    case .none:
      return Text("All quakes")
  }
}

因此，当我返回一般@Query private var quakes: [Quake]时，有一个数组返回数据.

使用Apple测试项目中包含的排序，quakes个被正确排序.

一旦我try 添加分组和排序，数据返回空array.

我是不是忽略了什么？