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我正在尝试更改为下游的主线程，但是在使用或.receive(on: DispatchQueue.main)时我没有收到输入。如果我不更改线程，我会收到正确的输入。.subscribe(:).sink(receiveValue:)

出版商

extension URLSessionWebSocketTask {
  struct ReceivePublisher: Publisher {
    typealias Output = Message
    typealias Failure = Error

    let task: URLSessionWebSocketTask

    func receive<S>(subscriber: S) where S: Subscriber, Output == S.Input, Failure == S.Failure {
      task.receive { result in
        switch result {
        case .success(let message): _ = subscriber.receive(message)
        case .failure(let error): subscriber.receive(completion: .failure(error))
        }
      }
    }
  }
}

extension URLSessionWebSocketTask {
  func receivePublisher() -> ReceivePublisher {
    ReceivePublisher(task: self)
  }
}

订户

extension ViewModel: Subscriber {
  typealias Input = URLSessionWebSocketTask.Message
  typealias Failure = Error

  func receive(subscription: Subscription) {}

  func receive(_ input: URLSessionWebSocketTask.Message) -> Subscribers.Demand {
    // Handle input here.
    // When using `.receive(on:)` this method is not called when should be.
    return .unlimited
  }

  func receive(completion: Subscribers.Completion<Error>) {}
}

订阅

socketTask.receivePublisher()
      .receive(on: DispatchQueue.main)
      .subscribe(viewModel)
socketTask.resume()
4

1 回答 1

2

AnyCancellable返回的 by将subscribe<S>(_ subject: S) -> AnyCancellable在cancel()它被取消初始化时调用。因此，如果您不保存它，它将在调用块超出范围时被取消初始化。

在我从 WWDC 看到的视频和教程中，从未解决过如何使用它。我所看到的是人们正在转向 RxSwift 的DisposeBag解决方案。

更新 Beta 4： Combine 现在带有一个AnyCancellable名为的方法：store(in:)这与我的旧解决方案几乎相同。您可以将AnyCancellables 存储在一组中AnyCancellable：

var cancellables = Set<AnyCancellable>()
...
override func viewDidLoad() {
    super.viewDidLoad()
    ...
    socketTask.receivePublisher()
        .receive(on: DispatchQueue.main)
        .subscribe(viewModel)
        .store(in: &cancellables)
}

这样，AnyCancellable当包含的类被取消初始化时，数组（和所有 s）将被取消初始化。

过时的：

如果您想要一个Cancellable可以以更好的方式使用的所有 s 的解决方案，您可以这样扩展Cancellable：

extension Cancellable {

    func cancel(with cancellables: inout [AnyCancellable]) {
        if let cancellable = self as? AnyCancellable {
            cancellables.append(cancellable)
        } else {
            cancellables.append(AnyCancellable(self))
        }
    }

}
于 2019-06-30T16:39:44.860 回答