ios - 合并:像Future一样的发布者，但具有多个值(value)

Question

我有使用此方法的3d派对库(Firestore)

func listenToEvents(handler: ([Result], Error) -> Void)

此方法中的 handler被多次调用(在数据更新之后)。我想将其转换为 Publisher
现在是我的代码:

var resultsPublisher: AnyPublisher<[Result], Error> {
    Deferred { 
        Future { promise in
           libraryObject.listenToEvents { results, error in // called multiple times
              guard let results = results else {
                 promise(.failure(error))
                 return
              }

              // this can't be called several times,
              // because Future's promise is supposed to be called only once
              promise(.success(results))
           }
         }
    }
    .eraseToAnyPublisher()
}

因此，我的 Publisher仅产生一次值，因为 Future以这种方式工作。是否有其他 Publishers(或可能是其他方法)来完成此操作？

Answer 1

这是可能的替代方法。不需要Defer，cause subject lives idle, and can send (pass-through) as many values as libraryObject将继续存在。

使用Xcode 11.4测试。

var resultsPublisher: AnyPublisher<[Result], Error> {
    let subject = PassthroughSubject<[Result], Error>()
    libraryObject.listenToEvents { results, error in // called multiple times
        guard let results = results else {
            subject.send(completion: .failure(error))
            return
        }

        subject.send(results)
    }
    return subject.eraseToAnyPublisher()
}