Swift Combine 的 CombineLatest 不会响应对其发布者之一的更新而触发

Question

我正在合并两个发布者以确定 map View 的中心坐标应该是什么。这两家出版商是:

1. 用户的初始位置由 CLLocationManager 确定(CLLocationManager 开始发送位置更新后报告的第一个位置)。
2. 如果点击“在当前位置居中 map ”按钮，则为用户的当前位置。

在代码中:

    class LocationManager: NSObject, ObservableObject {

        // The first location reported by the CLLocationManager.
        @Published var initialUserCoordinate: CLLocationCoordinate2D?
        // The latest location reported by the CLLocationManager.
        @Published var currentUserCoordinate: CLLocationCoordinate2D?
        // What the current map view center should be.
        @Published var coordinate: CLLocationCoordinate2D = CLLocationCoordinate2D(latitude: 42.35843, longitude: -71.05977) // Default coordinate.

        // A subject whose `send(_:)` method is being called elsewhere every time the user presses a button to center the map on the user's location.
        var centerButtonTappedPublisher: PassthroughSubject<Bool, Never> = PassthroughSubject<Bool, Never>()

        // The combined publisher that is where all my troubles lie.
        var coordinatePublisher: AnyPublisher<CLLocationCoordinate2D, Never> {
            Publishers.CombineLatest($initialUserCoordinate, centerButtonTappedPublisher)
                .map { initialCoord, centerButtonTapped in
                    var latestCoord = initialCoord
                    if centerButtonTapped {
                        latestCoord = self.currentUserCoordinate
                    }
                    return latestCoord
                }
                .replaceNil(with: CLLocationCoordinate2D(latitude: 42.35843, longitude: -71.05977))
                .eraseToAnyPublisher()
        }

        private var cancellableSet: Set<AnyCancellable> = []

        //... Other irrelevant properties

        private override init() {
            super.init()

            coordinatePublisher
                .receive(on: RunLoop.main)
                .assign(to: \.coordinate, on: self)
                .store(in: &cancellableSet)

            //... CLLocationManager set-up
        }
    }

    extension LocationManager: CLLocationManagerDelegate {

        //...

        func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
            // We are only interested in the user's most recent location.
            guard let location = locations.last else { return }
            let latestCoord = location.coordinate
            if initialUserCoordinate == nil {
                initialUserCoordinate = latestCoord
            }
            currentUserCoordinate = latestCoord
        }

        //...

    }

$initialUserCoordinate 和 centerButtonTappedPublisher 这两个发布者都发布了更新 - 我已经确认了这一点。但是，合并的发布者 coordinatePublisher 仅在点击“当前位置的中心 map ”按钮时触发。当首次设置 initialUserCoordinate 属性时，它永远不会触发。

This question建议在 Publishers.CombineLatest($initialUserCoordinate, centerButtonTappedPublisher) 之后添加一个 .receive(on: RunLoop.main) 但这对我不起作用。

我做错了什么？

Answer 1

您需要使用 Publishers.Merge而不是 CombineLatest ，请参阅文档:

对于 Publishers.CombineLatest:

A publisher that receives and combines the latest elements from two publishers.

对于 Publishers.Merge

A publisher that emits an event when either upstream publisher emits an event.