SwiftUI Picker 不与 ObservedObject 绑定(bind)

Question

我正在尝试使用从外部 API 异步获取的数据填充选择器。

这是我的模型:

struct AppModel: Identifiable {
    var id = UUID()
    var appId: String
    var appBundleId : String
    var appName: String
    var appSKU: String
}

获取数据并发布的类是:

class AppViewModel: ObservableObject {
    private var appStoreProvider: AppProvider? = AppProvider()
    @Published private(set) var listOfApps: [AppModel] = []
    @Published private(set) var loading = false

    fileprivate func fetchAppList() {
        self.loading = true
        appStoreProvider?.dataProviderAppList { [weak self] (appList: [AppModel]) in
            guard let self = self else {return}
            DispatchQueue.main.async() {
                self.listOfApps = appList
                self.loading = false
            }
        }
    }
    init() {
        fetchAppList()
    }
}

View 是:

struct AppView: View {
    @ObservedObject var appViewModel: AppViewModel = AppViewModel()
    @State private var selectedApp = 0

    var body: some View {
        ActivityIndicatorView(isShowing: self.appViewModel.loading) {
            VStack{
                // The Picker doesn't bind with appViewModel
                Picker(selection: self.$selectedApp, label: Text("")) {
                    ForEach(self.appViewModel.listOfApps){ app in
                        Text(app.appName).tag(app.appName)
                    }
                }
                // The List correctly binds with appViewModel
                List {
                    ForEach(self.appViewModel.listOfApps){ app in
                        Text(app.appName.capitalized)
                    }
                }
            }
        }
    }
}

虽然 List View 与观察对象 appViewModel 绑定(bind)，但 Picker 的行为方式不同。我不明白为什么。有什么帮助吗？

Answer 1

我提交了错误报告，FB7670992。 Apple 昨天回应，建议我在 iOS 14 beta 1 中确认此行为。现在看来已经解决。

struct ContentView: View {
    @ObservedObject var viewModel = ViewModel()

    var body: some View {
        Picker("", selection: $viewModel.wheelPickerValue) {
            ForEach(viewModel.objects) { object in
                Text(object.string)
            }
        }
        .pickerStyle(WheelPickerStyle())
        .labelsHidden()
    }
}

在哪里

struct Object: Identifiable {
    let id = UUID().uuidString
    let string: String
}

class ViewModel: ObservableObject {
    private var counter = 0

    @Published private(set) var objects: [Object] = []
    @Published var segmentedPickerValue: String = ""
    @Published var wheelPickerValue: String = ""

    fileprivate func nextSetOfValues() {
        let newCounter = counter + 3
        objects = (counter..<newCounter).map { value in Object(string: "\(value)") }
        let id = objects.first?.id ?? ""
        segmentedPickerValue = id
        wheelPickerValue = id
        counter = newCounter
    }

    init() {
        let timer = Timer.scheduledTimer(withTimeInterval: 2, repeats: true) { [weak self] timer in
            guard let self = self else { timer.invalidate(); return }
            self.nextSetOfValues()
        }
        timer.fire()
    }
}

结果: