SwiftUI+Combine - 动态订阅发布者的字典

Question

在我的项目中，我拥有大量通过 grpc 流更新的项目。在应用程序内部有几个地方我将这些项目呈现给 UI，我想传播实时更新。

简化代码：

struct Item: Identifiable {
    var id:String = UUID().uuidString
    var name:String
    var someKey:String
    
    init(name:String){
        self.name=name
    }
}

class DataRepository {
    public var serverSymbols: [String: CurrentValueSubject<Item, Never>] = [:]
    
    // method that populates the dict
    func getServerSymbols(serverID:Int){
        someService.fetchServerSymbols(serverID: serverID){ response in
            response.data.forEach { (name,sym) in
                self.serverSymbols[name] = CurrentValueSubject(Item(sym))
            }
        }
    }

    // background stream that updates the values
    func serverStream(symbols:[String] = []){
        someService.initStream(){ update in
            DispatchQueue.main.async {
                self.serverSymbols[data.id]?.value.someKey = data.someKey
            }
        }
    }
     
}

视图模型：

class SampleViewModel: ObservableObject {
    @Injected var repo:DataRepository   // injection via Resolver

    // hardcoded value here for simplicity (otherwise dynamically added/removed by user)
    @Published private(set) var favorites:[String] = ["item1","item2"]

    func getItem(item:String) -> Item {         
        guard let item = repo.serverSymbols[item] else { return Item(name:"N/A")}
        return ItemPublisher(item: item).data
    }
}

class ItemPublisher: ObservableObject {
    @Published var data:Item = Item(name:"")
    private var cancellables = Set<AnyCancellable>()
    
    init(item:CurrentValueSubject<Item, Never>){
        item
            .receive(on: DispatchQueue.main)
            .assignNoRetain(to: \.data, on: self)
            .store(in: &cancellables)
    }
}

带有子视图的主视图：

struct FavoritesView: View {
    @ObservedObject var viewModel: QuotesViewModel = Resolver.resolve()
    var body: some View {
        VStack {
            ForEach(viewModel.favorites, id: \.self) { item in
                    FavoriteCardView(item: viewModel.getItem(item: item))
            }
        }
    }
}

struct FavoriteCardView: View {
    var item:Item
    var body: some View {
        VStack {
            Text(item.name)
            Text(item.someKey)   // dynamic value that should receive the updates
        }
    }
}

我肯定错过了一些东西，或者这是一个完全错误的方法，但是我的项目卡没有收到任何更新（我确认后端流处于活动状态并且 serverSymbols 字典正在更新）。任何建议将不胜感激！

Answer 1

我意识到我犯了一个错误 - 为了接收更新，我需要传递 ItemPublisher 本身。 （我从我的 viewModel 的方法中错误地返回了 ItemPublisher.data）

我已经重构了代码并让 ItemPublisher 使用项目密钥直接从我的存储库中提供数据，所以现在每张卡都使用发布者单独订阅。

现在的最终工作代码：

class SampleViewModel: ObservableObject {
    // hardcoded value here for simplicity (otherwise dynamically added/removed by user)
    @Published private(set) var favorites:[String] = ["item1","item2"]

}

MainView 和 CardView：

struct FavoritesView: View {
    @ObservedObject var viewModel: QuotesViewModel = Resolver.resolve()
    var body: some View {
        VStack {
            ForEach(viewModel.favorites, id: \.self) { item in
                    FavoriteCardView(item)
            }
        }
    }
}

struct FavoriteCardView: View {
    var itemName:String
    @ObservedObject var item:ItemPublisher
    
    init(_ itemName:String){
        self.itemName = itemName
        self.item = ItemPublisher(item:item)
    }
    var body: some View {
        let itemData = item.data
        VStack {
            Text(itemData.name)
            Text(itemData.someKey)   
        }
    }
}

最后，修改了 ItemPublisher：

class ItemPublisher: ObservableObject {
    @Injected var repo:DataRepository
    @Published var data:Item = Item(name:"")
    private var cancellables = Set<AnyCancellable>()
    
    init(item:String){
        self.data = Item(name:item)
        if let item = repo.serverSymbols[item] {
            self.data = item.value
            item.receive(on: DispatchQueue.main)
                .assignNoRetain(to: \.data, on: self)
                .store(in: &cancellables)
        }       
    }
}