Question

我想使用CLLocation计算当前位置和MKDirections.calculate列表之间的实际步行距离。但是，由于某种原因，函数末尾的return命令不会等待结果，而是尝试返回空变量。我的代码如下：

func getDistance (location1: CLLocation, location2: CLLocation) {
    let coordinates1 = location1.coordinate
    let placemark1 = MKPlacemark(coordinate: coordinates1)
    let sourceItem = MKMapItem(placemark: placemark1)
    let coordinates2 = location2.coordinate
    let placemark2 = MKPlacemark(coordinate: coordinates2)
    let destinationItem = MKMapItem(placemark: placemark2)

    let request = MKDirectionsRequest()
    request.source = sourceItem
    request.destination = destinationItem
    request.requestsAlternateRoutes = true
    request.transportType = .walking

    var distance: Double?

    let directions = MKDirections(request: request)
    directions.calculate { (response, error) in

        if var routeResponse = response?.routes {
            routeResponse.sort(by: {$0.expectedTravelTime < $1.expectedTravelTime})
            let quickestRoute: MKRoute = routeResponse[0]
            distance = Double(quickestRoute.distance)
        }
    }

    return distance //returns nil
}

然后，我想在这样的代码中使用该函数：

let myLocation = CLLocation(latitude: 47.0, longitude: 17.0)
let destinationArray = [CLLocation(latitude: 47.1, longitude: 17.1), CLLocation(latitude: 47.2, longitude: 17.2), CLLocation(latitude: 47.3, longitude: 17.3)]
var distanceArray: [Double] = []
for destination in destinationArray {
    distanceArray.append(getDistance(location1: myLocation, location2: destination))
}
return distanceArray

我尝试了闭包，但是它们没有用，因为我找不到返回distanceArray的方法（同样的错误，它没有等待闭包运行并返回空数组）。我也尝试了DispatchGroups，但它们没有效果（也许我以错误的方式实现了它们）。

非常感谢您的帮助。

谢谢。

Answer 1

directions.calculate是一个异步函数，因此您需要等待函数返回后才能返回计算出的距离。您应该使用完成处理程序来完成此操作……

func getDistance(location1: CLLocation, location2: CLLocation, completion: @escaping (Double) -> Void) {

    // etc 
    directions.calculate { (response, error) in

        if var routeResponse = response?.routes {
            routeResponse.sort(by: {$0.expectedTravelTime < $1.expectedTravelTime})
            let quickestRoute: MKRoute = routeResponse[0]

            completion(Double(quickestRoute.distance))
        }
    }
}

，然后您应该对距离数组执行类似的操作。您需要等待所有getDistance的调用返回，因此您可以为此使用DispatchGroup…

func getDistanceArray(completion: @escaping ([Double]) -> Void) {

    let group = DispatchGroup()
    var distanceArray: [Double] = []

    for destination in destinationArray {
        group.enter()
        getDistance(location1: myLocation, location2: destination) { distance in
            distanceArray.append(distance)
            group.leave()
        }
    }
    group.wait()
    completion(distanceArray)
}

您可以打电话给…

getDistanceArray { distanceArray in
    print(distanceArray)
}

Answer 2

尝试以下关闭操作：

func getDistance (location1: CLLocation, location2: CLLocation,
    completion: @escaping(Double?) -> Void) {

    let coordinates1 = location1.coordinate
    let placemark1 = MKPlacemark(coordinate: coordinates1)
    let sourceItem = MKMapItem(placemark: placemark1)
    let coordinates2 = location2.coordinate
    let placemark2 = MKPlacemark(coordinate: coordinates2)
    let destinationItem = MKMapItem(placemark: placemark2)

    let request = MKDirectionsRequest()
    request.source = sourceItem
    request.destination = destinationItem
    request.requestsAlternateRoutes = true
    request.transportType = .walking

    var distance: Double?

    let directions = MKDirections(request: request)
    directions.calculate { (response, error) in

        if var routeResponse = response?.routes {
            routeResponse.sort(by: {$0.expectedTravelTime < $1.expectedTravelTime})
            let quickestRoute: MKRoute = routeResponse[0]
            distance = Double(quickestRoute.distance)
            completion(distance)
        }
    }
}

用法：

    let myLocation = CLLocation(latitude: 47.0, longitude: 17.0)
    let destinationArray = [CLLocation(latitude: 47.1, longitude: 17.1), CLLocation(latitude: 47.2, longitude: 17.2), CLLocation(latitude: 47.3, longitude: 17.3)]
    var distanceArray: [Double] = []
    for destination in destinationArray {
        getDistance(location1: myLocation, location2: destination) { distance in
            print("distance", distance)
            if let distance = distance {
                distanceArray.append(distance)
            }
        }
    }
    return distanceArray

Answer 3

使用MapKit和Swift 5

计算两个位置之间的距离，它将为任何人提供帮助

示例功能：我已经在Google Map和Apple Map中进行了测试

                    self.getDistance(departureDate: trip.departure.dateTime, arrivalDate: trip.arrival.dateTime, startLocation: startLocation, endLocation: endLocation) { (actualDistance) in
                        print("actualDistance : \(actualDistance)")
                    }

功能使用

func calculateDistancefrom(departureDate: Date, arrivalDate: Date, sourceLocation: MKMapItem, destinationLocation: MKMapItem, doneSearching: @escaping (_ distance: CLLocationDistance) -> Void) {

        let request: MKDirections.Request = MKDirections.Request()

        request.departureDate = departureDate
        request.arrivalDate = arrivalDate

        request.source = sourceLocation
        request.destination = destinationLocation

        request.requestsAlternateRoutes = true
        request.transportType = .automobile

        let directions = MKDirections(request: request)
        directions.calculate { (directions, error) in
            if var routeResponse = directions?.routes {
                routeResponse.sort(by: {$0.expectedTravelTime <
                    $1.expectedTravelTime})
                let quickestRouteForSegment: MKRoute = routeResponse[0]

                doneSearching(quickestRouteForSegment.distance)
            }
        }
    }

    func getDistance(departureDate: Date, arrivalDate: Date, startLocation : CLLocation, endLocation : CLLocation, completionHandler: @escaping (_ distance: CLLocationDistance) -> Void) {

        let destinationItem =  MKMapItem(placemark: MKPlacemark(coordinate: startLocation.coordinate))
        let sourceItem      =  MKMapItem(placemark: MKPlacemark(coordinate: endLocation.coordinate))
        self.calculateDistancefrom(departureDate: departureDate, arrivalDate: arrivalDate, sourceLocation: sourceItem, destinationLocation: destinationItem, doneSearching: { distance in
            completionHandler(distance)
        })
    }

我对上述功能进行了改进，并在此处添加了代码，希望对您有所帮助。

 <fragment
    android:id="@+id/youtube_frag"
    android:name="com.google.android.youtube.player.YouTubePlayerFragment"
    android:layout_width="match_parent"
    android:layout_height="150dp"
    android:layout_marginTop="5dp"
    android:layout_marginBottom="5dp"
    />

无法等待MKDirections.calculate的结果，得到nil而不是它

3 个答案: