ReactiveCocoa - SignalProducer 发出数组中最新的 N 个值

Question

我有一个 SignalProducer ProducerA，它以不同的时间间隔发出值。我正在尝试收集 SignalProducer 发出的最新 N 值并创建一个新的生产者 ProducerB，它发出包含最新 N 值的数组。

ProducerB 应在 ProducerA 发出前 N 个值时开始发出值，然后每次 ProducerA 发出新值时发出一个新数组。

有人可以帮助我吗？

Answer 1

let (producerA, observerA) = SignalProducer<Int, NoError>.buffer(5)
let n = 3

producerA.take(n).collect()
        .takeUntilReplacement(producerA.skip(n).map { [$0] })
        .scan([], { $0.suffix(n - 1) + $1 })
        .startWithNext {
                print($0)
}

observerA.sendNext(1) // nothing printed
observerA.sendNext(2) // nothing printed
observerA.sendNext(3) // prints [1, 2, 3]
observerA.sendNext(4) // prints [2, 3, 4]
observerA.sendNext(5) // prints [3, 4, 5]

Answer 2

我想出了这个代码

extension SignalProducer {
    /// Creates a new producer that emits an array that contains the latest N values that were emitted 
    /// by the original producer as specified in 'capacity'.
    @warn_unused_result(message="Did you forget to call `start` on the producer?")
    public func latestValues(n:Int) -> SignalProducer<[Value], Error> {
        var array: [Value] = []
        return self.map {
            value in

            array.append(value)

            if array.count >= n {
                array.removeFirst(array.count - n)
            }

            return array
        }
            .filter {
                $0.count == n
        }
    }
}

Answer 3

extension SignalProducer {
    func latestValues(count: Int) -> SignalProducer<[Value], Error> {
        SignalProducer<[Value], Error> { (observer: Signal<[Value], Error>.Observer, lifetime: Lifetime) in
            var collectedValues: [Value] = []
            
            let disposable = self
                .start(Signal<Value, Error>.Observer(value: { value in
                    collectedValues.append(value)
                    
                    if collectedValues.count > count {
                        collectedValues.removeFirst(collectedValues.count - count)
                    }
                    
                    if collectedValues.count == count {
                        observer.send(value: collectedValues)
                    }
                },
                                                     failed: { error in
                    observer.send(error: error)
                },
                                                     completed: {
                    observer.sendCompleted()
                },
                                                     interrupted: {
                    observer.sendInterrupted()
                }))
            
            lifetime.observeEnded {
                disposable.dispose()
            }
        }
    }
}

它发出一个包含最新 N 个值的数组。

测试：

let valuesGenerator = SignalProducer([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
    .promoteError(Error.self)

valuesGenerator
    .latestValues(count: 3)
    .start(Signal.Observer(value: { value in
        print("valuesGenerator, date: \(Date()), value: \(value)")
    },
                           failed: { error in
        print("valuesGenerator, date: \(Date()), error: \(error)")
    },
                           completed: {
        print("valuesGenerator, date: \(Date()), completed")
    },
                           interrupted: {
        print("valuesGenerator, date: \(Date()), interrupted")
    }))

输出：

valuesGenerator, date: 2024-10-22 11:16:15 +0000, value: [1, 2, 3]
valuesGenerator, date: 2024-10-22 11:16:15 +0000, value: [2, 3, 4]
valuesGenerator, date: 2024-10-22 11:16:15 +0000, value: [3, 4, 5]
valuesGenerator, date: 2024-10-22 11:16:15 +0000, value: [4, 5, 6]
valuesGenerator, date: 2024-10-22 11:16:15 +0000, value: [5, 6, 7]
valuesGenerator, date: 2024-10-22 11:16:15 +0000, value: [6, 7, 8]
valuesGenerator, date: 2024-10-22 11:16:15 +0000, value: [7, 8, 9]
valuesGenerator, date: 2024-10-22 11:16:15 +0000, value: [8, 9, 10]
valuesGenerator, date: 2024-10-22 11:16:21 +0000, completed