MKDirections calculateWithCompletionHandler

Question

I'm attempting to make an MKDirections request inside of a function and then return that value.

This is what I have so far

func requestETA(userCLLocation: CLLocation, coordinate: CLLocationCoordinate2D) -> String {
    let request = MKDirectionsRequest()

    // code setting up directions request, not important or relevant

    let directions = MKDirections(request: request)

    var travelTime = "Not Available"

        directions.calculate { response, error in
            if let route = response?.routes.first {
                travelTime = "\(route.expectedTravelTime/60)"
                print(travelTime)
            } else {
                travelTime = "0"
            }
        }
    print(travelTime)
    return travelTime
}

I'm aware MKDirections runs asynchronously and so currently this returns before the directions request has finished. How would I make the return statement wait for some sort of completion handler?

Also aware this question has been answered rather vaguely here stackoverflow in a very general way. I've been unable to figure out how to apply that answer to this specific problem.

Answer 1

You can add a completion handler to pass an optional string and an error as follow:

func requestETA(userCLLocation: CLLocation, coordinate: CLLocationCoordinate2D, completion: @escaping (_ string: String?, _ error: Error?) -> () ) {
    let request = MKDirectionsRequest()
    // code setting up directions request
    let directions = MKDirections(request: request)
    var travelTime: String?
    directions.calculate { response, error in
        if let route = response?.routes.first {
            travelTime = String(route.expectedTravelTime/60)
        }
        completion(travelTime, error)
    }
}

---

usage

requestETA(userCLLocation: location, coordinate: coordinate) { (travelTime, error) in
    guard let travelTime = travelTime, error == nil else { return }
    print(travelTime)
}