我试图用.receive(on: DispatchQueue.main)切换到下游的主线程,但是当使用.subscribe(:).sink(receiveValue:)时,我没有收到输入。如果我不改变线程,我会收到正确的输入。
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)
  }
}

用户
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()

最佳答案

AnyCancellable返回的subscribe<S>(_ subject: S) -> AnyCancellable在被取消初始化时将调用cancel()因此,如果不保存它,当调用块超出范围时,它将被取消初始化。
在我从WWDC看到的视频和教程中,如何处理这个问题从未提到过。我所看到的是,人们正在向RxSwift的DisposeBag解决方案漂移。
更新Beta 4:
Combine现在提供了一个名为:AnyCancellable的方法,它与我以前的解决方案差不多。您可以将store(in:)存储在一组AnyCancellable中:

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

这样,当包含类被取消初始化时,数组(以及所有AnyCancellables)将被取消初始化。
过时的:
如果您希望所有AnyCancellables的解决方案都能以更好的方式使用,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))
        }
    }

}

关于ios - 使用`.receive(on:DispatchQueue.main)`时不接收输入,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/56677669/

10-10 20:26