SwiftUI CurrentValueSubject 行为

Question

我是 SwiftUI 的新手。我与 UIKit 和组合框架一起使用 ViewModel、UseCases 和 Repositories 构建架构。我所有的架构都是基于加载状态。我的加载状态是这样构建的：

/// Equivalent to @Published with `LoadingState<T, E>` property wrapper
@propertyWrapper public class Loading<T, E: Swift.Error> {
public typealias State = LoadingState<T, E>

public var wrappedValue: State {
    willSet {
        subject.send(newValue)
    }
}

public init(wrappedValue: State) {
    self.wrappedValue = wrappedValue
}

private lazy var subject = CurrentValueSubject<State, Never>(wrappedValue)

public var projectedValue: AnyPublisher<State, Never> {
    return subject.eraseToAnyPublisher()
}
}

我的 ViewModel 以这种方式工作：

@Loading<MyData, MyError> var myDataLoadingState = .idle
public func getMyData(ID: String) {
    myDataLoadingState = .loading
    
    myDataUseCase.execute(ID: ID)
        .receive(on: DispatchQueue.main)
        .sink { completion in
            guard case .failure(let error) = completion else { return }
            myDataLoadingState = .failure(error)
        } receiveValue: { myData in
            self. myDataLoadingState = .success(myData)
        }
        .store(in: &self.cancellables)
}

控制器是这样工作的：

viewModel.$myDataLoadingState
       .sink { state in
           switch state {
           case .idle:
            break
           case .loading:
             self.showLoader()
           case .success(let myData):
            print(myData)
           case .failure(let error):
            self.print(error)
            self.hideLoader()
           }
       }
       .store(in: &cancellables)

我可以在 SwiftUI 中使用加载状态和我的 ViewModel 吗？我尝试过这种方式但似乎不起作用：

struct ContentView: View {
@StateObject var viewModel: MyViewModel

var body: some View {
    switch viewModel.loadingState {
    case .idle:
        Text("Idle")
    case .loading:
        Text("Loading")
    case .success(let myData):
        Text(myData.name)
    case .failure(let error):
        Text(error.localizedDescription)
    }
}
}

ViewModel 现在是 ObservableObject

public class MyViewModel: ObservableObject {

}

提前致谢

Answer 1

刚刚认识到您已经拥有myDataLoadingState 的属性包装器，因此不确定您是否可以改为使用@Published。无论如何，要通知 @StateObject 包装器（谁是听众），您应该触发有关视图模型更改的事件。一种可能的方法是直接使用objectWillChange，比如

myDataUseCase.execute(ID: ID)
    .receive(on: DispatchQueue.main)
    .sink { completion in
        guard case .failure(let error) = completion else { return }

        self.objectWillChange.send()             // << here !!
        myDataLoadingState = .failure(error)
    } receiveValue: { myData in
        self.objectWillChange.send()             // << here !!
        self.myDataLoadingState = .success(myData)
    }
    .store(in: &self.cancellables)