我正在合并两个发布者，以确定地图视图的中心坐标应该是什么。两家出版商是：
import cv2
url = "http://192.168.43.1:8080" # Your url might be different, check the app
vs = cv2.VideoCapture(url+"/video")
while True:
ret, frame = vs.read()
if not ret:
continue
# Processing of image and other stuff here
cv2.imshow('Frame', frame)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
确定的用户的初始位置（CLLocationManager开始发送位置更新后报告的第一个位置）。在代码中：
CLLocationManager 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($initialUserCoordinate, centerButtonTappedPublisher)
.map { initialCoord, centerButtonTapped in
var latestCoord = initialCoord
if centerButtonTapped {
latestCoord = self.currentUserCoordinate
}
return latestCoord
}
.replaceNil(with: CLLocationCoordinate2D(latitude: 42.35843, longitude: -71.05977))
.eraseToAnyPublisher()
}
private var cancellableSet: Set<AnyCancellable> = []
//... Other irrelevant properties
private override init() {
super.init()
coordinatePublisher
.receive(on: RunLoop.main)
.assign(to: \.coordinate, on: self)
.store(in: &cancellableSet)
//... CLLocationManager set-up
}
}
extension LocationManager: CLLocationManagerDelegate {
//...
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
// We are only interested in the user's most recent location.
guard let location = locations.last else { return }
let latestCoord = location.coordinate
if initialUserCoordinate == nil {
initialUserCoordinate = latestCoord
}
currentUserCoordinate = latestCoord
}
//...
}
和$initialUserCoordinate这两个发布商都发布了更新-我已经确认了这一点。但是，只有在点击“当前位置的中心地图”按钮后，才会触发合并的发布者centerButtonTappedPublisher。首次设置coordinatePublisher属性时，它永远不会触发。
This question建议在initialUserCoordinate之后添加.receive(on: RunLoop.main)，但这对我不起作用。
我在做什么错了？
答案 0 :(得分：1)
您需要使用Publishers.Merge而不是CombineLatest，请参阅文档：
对于Publishers.CombineLatest：
从两个发布者那里接收并合并最新元素的发布者。
对于Publishers.Merge
在任一上游发布者发出事件时发出事件的发布者。