Apple Mapkit calculateETAWithCompletionHandler loop through array - ios

Question

I am making an application where when you click a button it populates a tableview with all of the Users and their estimated ETA from you. I keep running into an issue when I'm looping through my users and getting their location it doesn't make the Array in the same order that its looping through and therefore the times become all mixed up. I've tried several different ways of looping through them but it seems like when it gets the directions.calculateETA section it is delayed and runs at different times. Can anyone help me run through this efficiently so the loop doesn't run out of order?
for user in usersArray {
var userLocations:CLLocationCoordinate2D = CLLocationCoordinate2D(latitude: user["location"].latitude, longitude: user["location"].longitude)
ETARequest(userLocations)
}
func ETARequest(destination:CLLocationCoordinate2D) {
let request = MKDirectionsRequest()
if let currentLocation = self.manager.location?.coordinate {
request.source = MKMapItem(placemark: MKPlacemark(coordinate: currentLocation, addressDictionary: nil))
request.destination = MKMapItem(placemark: MKPlacemark(coordinate: destination, addressDictionary: nil))
request.transportType = .Automobile
let directions = MKDirections(request: request)
directions.calculateETAWithCompletionHandler({ ( response, error) in
if error == nil {
if let interval = response?.expectedTravelTime {
print(self.formatTimeInterval(interval))
self.durationArray.insert(self.formatTimeInterval(interval), atIndex: 0)
if self.durationArray.count == self.allUsers.count {
print(self.durationArray)
self.tableView.reloadData()
}
}
} else {
print("Error Occurred")
}
})
}
}

Answer 1

The issue here is that calculateETAWithCompletionHandler makes a network request. It's an asynchronous function, so you can't assume that all your calls to it will return in the same order you sent them. Here's one solution to this problem:
If you have a user object with an optional duration property, you can refactor your ETARequest method to take one as input:
func ETARequest(destination:CLLocationCoordinate2D, user: UserType) {
//Do stuff...
}
Then, in the completion handler block you pass to calculateETAWithCompletionHandler, you can replace self.durationArray.insert(self.formatTimeInterval(interval), atIndex: 0) with user.duration = self.formatTimeInterval(interval). (You can still have a counter to determine when all requests have finished.)
This way, each user will have a duration associated with it, and you can display them accordingly by looping through your users in the desired order.