Swift Combine：在未调用序列发布者之后收集

Question

I have a subject which sends/receives an array of Data like PassthroughSubject<[Int], Never>() . When a value is received I want to split the array in single values to manipulate them and afterwards collect them again.

I know that the issue is that the flatMap never sends the completion Event. But how can I solves this issue? Or is there a better way to manipulate every value in an array with combine?

Edit: I don't want to complete the subject to collect. I want to collect the output of the sequencer.

Example:

import Combine

var storage = Set<AnyCancellable>()
let subject = PassthroughSubject<[Int], Never>()

subject
    .flatMap { $0.publisher }
    .map { $0 * 10 }
    .collect()
    .sink {
        print($0) // Never called
    }
    .store(in: &storage)

subject.send([1, 2, 3, 4, 5])

Answer 1

I found a solution how I achieved the my expected outcome. I had to move the map and collect within the flatMap .

import Combine

var storage = Set<AnyCancellable>()
let subject = PassthroughSubject<[Int], Never>()

subject
    .flatMap { $0.publisher
        .map { $0 * 10 }
        .collect()
    }
    .sink {
        print($0)
    }
    .store(in: &storage)

subject.send([1, 2, 3, 4, 5])
subject.send([1, 2, 3, 4, 5].reversed())

This will print [10, 20, 30, 40, 50] and [50, 40, 30, 20, 10] .

Answer 2

collect waits for the publisher to complete. A PassthroughSubject doesn't automatically complete. You need to call send(completion: on it.

subject.send([1, 2, 3, 4, 5])
subject.send(completion: .finished) // now `sink` will be triggered

Answer 3

You don't need the flatMap() and the collect() calls, you can simply map() over the received array:

subject
    .map { $0.map { $0 * 10 } }
    .sink {
        print($0) // Now it's called :)
    }
    .store(in: &storage)

subject.send([1, 2, 3, 4, 5])