ObservableObject 内的 ObservedObject 不刷新视图

Question

我正在尝试在执行异步请求时显示活动指示器。我所做的是创建一个 ActivityTracker 对象来跟踪发布者的生命周期。这个 ActivityTracker 是一个 ObservableObject 并将存储在视图模型中，它也是一个 ObservableObject。

似乎这种设置并没有刷新视图。这是我的代码：

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

    var body: some View {
        VStack(spacing: 16) {
            Text("Counter: \(viewModel.tracker.count)\nPerforming: \(viewModel.tracker.isPerformingActivity ? "true" : "false")")

            Button(action: {
                _ = request().trackActivity(self.viewModel.tracker).sink { }
            }) {
                Text("Request")
            }
        }
    }
}

class ContentViewModel: ObservableObject {
    @Published var tracker = Publishers.ActivityTracker()
}

private func request() -> AnyPublisher<Void, Never> {
    return Just(()).delay(for: 2.0, scheduler: RunLoop.main)
        .eraseToAnyPublisher()
}

extension Publishers {
    final class ActivityTracker: ObservableObject {
        // MARK: Properties

        @Published var count: Int = 0

        var isPerformingActivity: Bool {
            return count > 0
        }

        private var cancellables: [AnyCancellable] = []
        private let counterSubject = CurrentValueSubject<Int, Never>(0)
        private let lock: NSRecursiveLock = .init()

        init() {
            counterSubject.removeDuplicates()
                .receive(on: RunLoop.main)
                .print()
                .sink { [weak self] counter in
                    self?.count = counter
                }
                .store(in: &cancellables)
        }

        // MARK: Private methods

        fileprivate func trackActivity<Value, Error: Swift.Error>(
            ofPublisher publisher: AnyPublisher<Value, Error>
        ) {
            publisher
                .receive(on: RunLoop.main)
                .handleEvents(
                    receiveSubscription: { _ in self.increment() },
                    receiveOutput: nil,
                    receiveCompletion: { _ in self.decrement() },
                    receiveCancel: { self.decrement() },
                    receiveRequest: nil
                )
                .print()
                .sink(receiveCompletion: { _ in }, receiveValue: { _ in })
                .store(in: &cancellables)
        }

        private func increment() {
            lock.lock()
            defer { lock.unlock() }
            counterSubject.value += 1
        }

        private func decrement() {
            lock.lock()
            defer { lock.unlock() }
            counterSubject.value -= 1
        }
    }
}

extension AnyPublisher {
    func trackActivity(_ activityTracker: Publishers.ActivityTracker) -> AnyPublisher {
        activityTracker.trackActivity(ofPublisher: self)
        return self
    }
}

我也尝试将我的 ActivityTracker 声明为@Published相同的结果，我的文本没有更新。请注意，将活动跟踪器直接存储在视图中会起作用，但这不是我想要的。

我在这里错过了什么吗？

Answer 1

目前还不支持嵌套的 ObservableObjects。当您要使用这些嵌套对象时，您需要在数据发生更改时自行通知对象。我希望以下代码可以帮助您解决问题。

首先使用： import Combine

然后声明你的模型和子模型，它们都需要使用该@ObservableObject属性才能工作。（不要忘记@Published财产aswel）

我制作了一个名为Model的父模型和两个子模型Submodel1 和 Submodel2。当您在更改数据 ex: 时使用父模型时model.submodel1.count，您需要使用通知程序以便让 View 自行更新。

该AnyCancellables通知本身父模型，在这种情况下，视图将自动更新。

复制代码并自己使用，然后在使用时尝试重新编写代码。希望这有帮助，祝你好运！

class Submodel1: ObservableObject {
  @Published var count = 0
}

class Submodel2: ObservableObject {
  @Published var count = 0
}

class Model: ObservableObject {
  @Published var submodel1 = Submodel1()
  @Published var submodel2 = Submodel2()
    
    var anyCancellable: AnyCancellable? = nil
    var anyCancellable2: AnyCancellable? = nil

    init() {
        
        anyCancellable = submodel1.objectWillChange.sink { [weak self] (_) in
            self?.objectWillChange.send()
        }
        
        anyCancellable2 = submodel2.objectWillChange.sink { [weak self] (_) in
            self?.objectWillChange.send()
        }
    }
}

当你想使用这个Model 时，就像正常使用 ObservedObjects 一样使用它。

struct Example: View {

@ObservedObject var obj: Model

var body: some View {
    Button(action: {
        self.obj.submodel1.count = 123
        // If you've build a complex layout and it still won't work, you can always notify the modal by the following line of code:
        // self.obj.objectWillChange.send()
    }) {
        Text("Change me")
    }
}

Answer 2

如果你有一些东西的集合，你可以这样做：

import Foundation
import Combine

class Submodel1: ObservableObject {
    @Published var count = 0
}

class Submodel2: ObservableObject {
    var anyCancellable: [AnyCancellable] = []
    @Published var submodels: [Submodel1] = []

    init() {
        submodels.forEach({ submodel in
            anyCancellable.append(submodel.objectWillChange.sink{ [weak self] (_) in
                self?.objectWillChange.send()
            })
        })
    }
}