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I am building a navigation app that prompts the user to turn on location services. If the user selects no to turning them on and he/she returns back to my app, my app refuses to launch the same prompt to turn on location services when I put a call to locationManager.requestWhenInUseAuthorization() in prepare(for:send) before segue transition is executed.

Can anyone suggest why the turn on location services alert is not displayed in prepare(for:sender)?

Thanks.

//
// CountiesTableVC.swift
// TableViewsApp
//
// Created by Stephen Learmonth on 10/12/2018.
// Copyright © 2018 Stephen Learmonth. All rights reserved.
//

import UIKit
import CoreLocation
import MapKit

class CountiesTableVC: UITableViewController 

 let england : England = England()
 var countiesArray : [String] = ["Northamptonshire",
 "Bedfordshire",
 "Hertfordshire",
 "Staffordshire",
 "Essex",
 "North Yorkshire",
 "Herefordshire",
 "Cornwall",
 "Dorset",
 "Derbyshire",
 "Leicestershire",
 "Lancashire",
 "Cheshire",
 "Merseyside",
 "Suffolk",
 "County Durham",
 "Cumbria",
 "Gloucestershire",
 "Wiltshire",
 "Nottinghamshire",
 "Devon",
 "Somerset",
 "Lincolnshire"
 ]
 var sortedCounties : [ String ] = []

 var selectedCounty : String? = nil

 var currentCoordinate: CLLocationCoordinate2D! = nil
 var locationManager = CLLocationManager()

 override func viewDidLoad() 

 super.viewDidLoad()

 locationManager.delegate = self
 locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation
 locationManager.distanceFilter = 10.0
//
// print("inside viewDidLoad() BEFORE IF authorizationStatus = (CLLocationManager.authorizationStatus().rawValue)")
//
 if CLLocationManager.authorizationStatus() != .authorizedWhenInUse 
//
// print("inside viewDidLoad() & IF BEFORE call: authorizationStatus = (CLLocationManager.authorizationStatus().rawValue)")
//
// // prompts user to turn on location services
 locationManager.requestWhenInUseAuthorization()
//
// print("inside viewDidLoad() & IF AFTER call: authorizationStatus = (CLLocationManager.authorizationStatus().rawValue)")
 

 sortedCounties = countiesArray.sorted $0 < $1 

 

 // MARK: - Table view data source

 override func numberOfSections(in tableView: UITableView) -> Int 
 // #warning Incomplete implementation, return the number of sections
 return 1
 

 override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int 
 // #warning Incomplete implementation, return the number of rows
 return sortedCounties.count
 


 override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell 

 let cell = tableView.dequeueReusableCell(withIdentifier: "CountyTableViewCell", for: indexPath) as! CountyTableViewCell

 let county = sortedCounties[indexPath.row]
 let countySites = england.counties[county]
 var siteIsSelectable = false
 if (countySites?.isEmpty)! == true 

 cell.backgroundColor = .gray
 cell.isUserInteractionEnabled = false

 else 

 siteIsSelectable = true
 cell.backgroundColor = .blue
 cell.isUserInteractionEnabled = true

 

 cell.setLabel(cellLabel: sortedCounties[indexPath.row], selectable: siteIsSelectable)

 return cell
 

 // In a storyboard-based application, you will often want to do a little preparation before navigation
 override func prepare(for segue: UIStoryboardSegue, sender: Any?) 

 if segue.identifier == "toSitesTableVC" 

// if CLLocationManager.authorizationStatus() != .authorizedWhenInUse 
////
// print("prepare(for:sender) inside BEFORE: authorizationStatus = (CLLocationManager.authorizationStatus().rawValue)")
////
// locationManager.requestWhenInUseAuthorization()
//
// print("prepare(for:sender) AFTER: authorizationStatus = (CLLocationManager.authorizationStatus().rawValue)")
//
// // authorized location status when app is in use; update current location
// locationManager.startUpdatingLocation()
//
// 

 let sitesTableVC = segue.destination as? SitesTableVC

 if let indexPath = self.tableView.indexPathForSelectedRow 

 selectedCounty = sortedCounties[indexPath.row]
 sitesTableVC?.selectedCounty = selectedCounty
 sitesTableVC?.currentCoordinate = currentCoordinate

 

 

 return

 



extension CountiesTableVC: CLLocationManagerDelegate 

 func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) 

// print("inside locationManager(manager:didUpdateLocations")

 // get current location if available
 guard let currentLocation = locations.last else return 

// print("inside locationManager(manager:didUpdateLocations) authorizationStatus = (CLLocationManager.authorizationStatus().rawValue)")

 // get coordinates of current user location
 currentCoordinate = currentLocation.coordinate

 manager.stopUpdatingLocation()

 

 func locationManager(_ manager: CLLocationManager, didChangeAuthorization status: CLAuthorizationStatus) 

 if status != .authorizedWhenInUse 

// print("locationManager(manager:didChangeAuthorization) BEFORE: authorizationStatus = (CLLocationManager.authorizationStatus().rawValue)")
// print("locationManager(manager:didChangeAuthorization) BEFORE: status = (status.rawValue)")

 manager.requestWhenInUseAuthorization()

// print("locationManager(manager:didChangeAuthorization) AFTER: authorizationStatus = (CLLocationManager.authorizationStatus().rawValue)")
// print("locationManager(manager:didChangeAuthorization) AFTER: status = (status.rawValue)")

 

 // authorized location status when app is in use; update current location
 manager.startUpdatingLocation()

 return

 

You can request iOS up to 2 times for location services, If the user cancel to turn on location services both times, then next time app requests requestWhenInUseAuthorization no alert is displayed.

Here you can tell if user has disabled core location by calling CLLocationManager class method locationServicesEnabled. Then you can present your own custom alert to guide user to turn on location services manually from iOS settings app.

From the documentation:

When the current authorization status is CLAuthorizationStatus.notDetermined, this method runs asynchronously and prompts the user to grant permission to the app to use location services. The user prompt contains the text from the NSLocationWhenInUseUsageDescription key in your app’s Info.plist file, and the presence of that key is required when calling this method. After the status is determined, the location manager delivers the results to the delegate’s locationManager(_:didChangeAuthorization:) method. If the current authorization status is anything other than CLAuthorizationStatus.notDetermined, this method does nothing and does not call the locationManager(_:didChangeAuthorization:) method.

(emphasis mine)

ie. once your user has answered the permission dialog, it will never be shown again.