Async function not handled by completion handler

Question

I am using the google maps distance matrix api and using a compeletion handler to pass my async function calls like this:

func configureRoute(origin:String,destination:String, completionHandler: @escaping (_ duration:Int) -> ()){
    let jsonURL = "https://maps.googleapis.com/maps/api/distancematrix/json?units=imperial&origins=place_id:\(origin)&destinations=place_id:\(destination)&key=MYAPI"
    guard let url = URL(string: jsonURL ) else {return}
    print(jsonURL)

    URLSession.shared.dataTask(with: url) { (data, response, err) in
        guard let data = data else {return}
        do {
            let route = try JSONDecoder().decode(Welcome.self, from: data)
            // print(self.durations)
            completionHandler(route.rows[0].elements[0].duration.value)
        }
        catch let jsonErr {
        }
        let dataAsString = String(data: data, encoding: .utf8)
    }.resume()
}

and then I try and use that result like so, however my output results are still blank and I am unable to use any of the calls that I have received. I am not that good with compeltion handlers, so if anyone could let me know what I have done wrong?

func majorConfigure() {
    permutations(placeID.count, &placeID, origin: startPlaceID, destination: endPlaceID)
    for eachArray in finalRoutes {
        for i in 0..<(eachArray.count-1) {
            configureRoute(origin: eachArray[i], destination: eachArray[i+1]){
                duration in
                self.durations.append(duration)
            }
        }
        groupedDurations.append(durations)
        durations.removeAll()
    }
    print(groupedDurations)
}

After using Dispatch group this is my updated code:

 func majorConfigure(){
    permutations(placeID.count, &placeID, origin: startPlaceID, destination: endPlaceID)
    let dispatchGroup = DispatchGroup()
    for eachArray in finalRoutes{
        for i in 0..<(eachArray.count-1){
            dispatchGroup.enter()
            configureRoute(origin: eachArray[i], destination: eachArray[i+1]){
                duration in
                self.durations.append(duration)
                print(self.groupedDurations)
                dispatchGroup.leave()
            }
        }
        dispatchGroup.notify(queue: .main){
            self.groupedDurations.append(self.durations)
            self.durations.removeAll()
        }
    }

 }

The result when I print groupedDurations is:

[]
[]
[]
[]
[]
[]

have you tried the url in browser ? are you getting any response ? — Shahzaib Qureshi, Aug 06 '18 at 05:48

Shahzaib Qureshi · Answer 1 · 2018-08-07T18:50:37.110

give this a try :

    func majorConfigure() {
permutations(placeID.count, &placeID, origin: startPlaceID, destination: endPlaceID)
for eachArray in finalRoutes {
    for i in 0..<(eachArray.count-1) {
        configureRoute(origin: eachArray[i], destination: eachArray[i+1]){
            duration in
            self.durations.append(duration)
               if i == eachArray.count - 1{
                groupedDurations.append(durations)
               }
            if i == eachArray.count - 1 && eachArray == finalRoutes.last! {
                 print(groupedDurations)
                 durations.removeAll()
              } 
        }
    }


}

}

EDITED ANSWER

You can achieve this in this manner :

var indexFinalRoutes = 0 
var indexEachArray = 0

func loopFinalRoutes(){
    self.indexEachArray = 0
    let eachArray = finalRoutes[indexFinalRoutes]
    loopEachArray(eachArray: eachArray) { (success) in
        self.indexFinalRoutes = self.indexFinalRoutes + 1
        if self.indexFinalRoutes < self.finalRoutes.count - 1{
            self.loopFinalRoutes()
        }else{
            self.indexFinalRoutes = 0
            print(self.groupedDurations)
        }
    }
}

func loopEachArray(eachArray : [String] ,
                   completion: @escaping (_ success:Bool) -> Void){

    if indexEachArray + 1 < eachArray.count - 1 {
        configureRoute(origin: eachArray[indexEachArray], destination: eachArray[indexEachArray+1]){
            duration in
            self.durations.append(duration)
            self.indexEachArray = self.indexEachArray + 1
            let nextEachArray = self.finalRoutes[self.indexFinalRoutes]
            self.loopEachArray(eachArray: nextEachArray, completion: completion)
        }
    }else{
        groupedDurations.append(durations)
        durations.removeAll()
        completion(true)
    }

}

call loopFinalRoutes functuin from your majorConfigure function and you will have the output.

this function is using the completion handlers, check if it is printing groupDurations or not — Shahzaib Qureshi, Aug 06 '18 at 10:24
Well something strange happens. I put a breakpoint on the statement and it doesn't get called and nothing gets printed so I'm guessing the statement doesn't get called. — Arnav GUPTA, Aug 06 '18 at 13:12
I am getting an output, but when I input 4 destinations, the output is only a dictionary with one array, with 2 elements whereas the output should be one dictionary with 2 arrays with 3 elements each. Should I call loopFinalRoutes inside a loop or in majorConfigure itself? — Arnav GUPTA, Aug 14 '18 at 14:40

Async function not handled by completion handler

1 Answers1