Swiftui，核心数据和摄影：当状态更改时，视图不会更新（状态管理地狱）

Question

我正在通过构建照片组织者应用程序来学习Swift/Swiftui。它在网格中显示了用户的照片库，例如内置的照片应用程序，并且有一个详细的视图，您可以在其中做喜欢的照片或将其添加到垃圾箱中。

我的应用程序加载了所有数据并显示良好，但是当情况发生变化时，UI不会更新。我已经进行了足够的调试，以确认我的编辑应用于基础phassets和核心数据资产。 感觉问题是我的观点不是重新订阅。

我使用 dave deLong的方法创建一个将核心数据与Swiftui分开的抽象层。我有一个称为datastore的单例环境对象，可以处理与核心数据和phphotolibrary的所有交互。当应用程序运行时，创建了datastore。它制作AssetFetcher，从照片库中获取所有资产（并实现phphotolibraryChangeObserver）。 datastore在资产上迭代以在核心数据中创建索引。我的视图'viewModels查询索引项目的查询核心数据，并使用dave帖子中的@query属性包装器显示它们。

app.swift

@main
struct LbPhotos2App: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
                .environment(\.dataStore, DataStore.shared)
        }
    }
}

photogridview.swift（这是contentview呈现的内容）

struct PhotoGridView: View {
    @Environment(\.dataStore) private var dataStore : DataStore
    @Query(.all) var indexAssets: QueryResults<IndexAsset>
    @StateObject var vm = PhotoGridViewModel() 
    
    func updateVm() {
        vm.createIndex(indexAssets)
    }
    
    var body: some View {
        GeometryReader { geo in
            VStack {
                HStack {
                    Text("\(indexAssets.count) assets")
                    Spacer()
                    TrashView()
                }.padding(EdgeInsets(top: 4, leading: 16, bottom: 4, trailing: 16))
                ScrollView {
                    ForEach(vm.sortedKeys, id: \.self) { key in
                        let indexAssets = vm.index[key]
                        let date = indexAssets?.first?.creationDate
                        GridSectionView(titleDate:date, indexAssets:indexAssets!, geoSize: geo.size)
                    }
                }.onTapGesture {
                    updateVm()
                }
            }.onAppear {
                updateVm()
            }
            .navigationDestination(for: IndexAsset.self) { indexAsset in
                AssetDetailView(indexAsset: indexAsset)
            }
        }
    }
    
}

photogridViewModel.swift

class PhotoGridViewModel: ObservableObject {
    @Published var index: [String:[IndexAsset]] = [:]
    var indexAssets: QueryResults<IndexAsset>?
        
    func createIndex() {
        guard let assets = self.indexAssets else {return}
        self.createIndex(assets)
    }
    
    func createIndex(_ queryResults: QueryResults<IndexAsset>) {
        indexAssets = queryResults
        if queryResults.count > 0 {
            var lastDate = Date.distantFuture
            
            for i in 0..<queryResults.count {
                let item = queryResults[i]
                let isSameDay = isSameDay(firstDate: lastDate, secondDate: item.creationDate!)
                if isSameDay {
                    self.index[item.creationDateKey!]?.append(item)
                } else {
                    self.index[item.creationDateKey!] = [item]
                }
                lastDate = item.creationDate!
            }
        }
        self.objectWillChange.send()
        
    }
    
    var sortedKeys: [String] {
        return index.keys.sorted().reversed()
    }
    
    private func isSameDay(firstDate:Date, secondDate:Date) -> Bool {
        return Calendar.current.isDate(
            firstDate,
            equalTo: secondDate,
            toGranularity: .day
        )
    }

 }

我实际上在GridSectionView.swift

LazyVGrid(columns: gridLayout, spacing: 2) {
                let size = geoSize.width/4

                ForEach(indexAssets, id:\.self) { indexAsset in
                    NavigationLink(
                        value: indexAsset,
                        label: {
                            AssetCellView(indexAsset: indexAsset, geoSize:geoSize)
                        }
                    ).frame(width: size, height: size)
                        .buttonStyle(.borderless)
                }
            }

AssetCellview.swift

struct AssetCellView: View {
    @StateObject var vm : AssetCellViewModel
    var indexAsset : IndexAsset
    var geoSize : CGSize
    
    init(indexAsset: IndexAsset, geoSize: CGSize) {
        self.indexAsset = indexAsset
        self.geoSize = geoSize
        _vm = StateObject(wrappedValue: AssetCellViewModel(indexAsset: indexAsset, geoSize: geoSize))
    }
    
    
    var body: some View {
        ZStack(alignment: .bottomTrailing) {
            if (vm.indexAsset != nil && vm.image != nil) {
                vm.image?
                    .resizable()
                    .aspectRatio(contentMode: .fit)
                    .border(.blue, width: vm.indexAsset!.isSelected ? 4 : 0)
            }
            if (vm.indexAsset != nil && vm.indexAsset!.isFavorite) {
                Image(systemName:"heart.fill")
                    .resizable()
                    .frame(width: 20, height: 20)
                    .foregroundStyle(.ultraThickMaterial)
                    .shadow(color: .black, radius: 12)
                    .offset(x:-8, y:-8)
            }
        }
        
    }
}

AssetCellViewModel.swift
class AssetCellViewModel: ObservableObject{
    @Environment(\.dataStore) private var dataStore
    @Published var image : Image?
    var indexAsset : IndexAsset?
    var geoSize : CGSize
    
    init(indexAsset: IndexAsset? = nil, geoSize:CGSize) {
        self.indexAsset = indexAsset
        self.geoSize = geoSize
        self.requestImage(targetSize: CGSize(width: geoSize.width/4, height: geoSize.width/4))
    }
    
    func setIndexAsset(_ indexAsset:IndexAsset, targetSize: CGSize) {
        self.indexAsset = indexAsset
        self.requestImage(targetSize: targetSize)
    }
    
    func requestImage(targetSize: CGSize? = nil) {
        if (self.indexAsset != nil) {
            dataStore.fetchImageForLocalIdentifier(
                id: indexAsset!.localIdentifier!,
                targetSize: targetSize,
                completionHandler: { image in
                    withAnimation(Animation.easeInOut (duration:0.15)) {
                        self.image = image
                    }
                }
            )
        }
    }
}

dataTastore.swift

public class DataStore : ObservableObject {
    static let shared = DataStore()
    
    let persistenceController = PersistenceController.shared
    @ObservedObject var assetFetcher = AssetFetcher() 
    
    let dateFormatter = DateFormatter()
    var imageManager = PHCachingImageManager()
    let id = UUID().uuidString

    
    init() {
        print("