Check if location services are enabled

Add the CLLocationManagerDelegate to your class inheritance and then you can make this check:

Import CoreLocation Framework

import CoreLocation

Swift 1.x - 2.x version:

if CLLocationManager.locationServicesEnabled() {
    switch CLLocationManager.authorizationStatus() {
    case .NotDetermined, .Restricted, .Denied:
        print("No access")
    case .AuthorizedAlways, .AuthorizedWhenInUse:
        print("Access")
    }
} else {
    print("Location services are not enabled")
}

Swift 4.x version:

if CLLocationManager.locationServicesEnabled() {
     switch CLLocationManager.authorizationStatus() {
        case .notDetermined, .restricted, .denied:
            print("No access")
        case .authorizedAlways, .authorizedWhenInUse:
            print("Access")
     }
} else {
    print("Location services are not enabled")
}

Swift 5.1 version

if CLLocationManager.locationServicesEnabled() {
    switch CLLocationManager.authorizationStatus() {
        case .notDetermined, .restricted, .denied:
            print("No access")
        case .authorizedAlways, .authorizedWhenInUse:
            print("Access")
        @unknown default:
            break
    }
} else {
    print("Location services are not enabled")
}

iOS 14.x

In iOS 14 you will get the following error message: authorizationStatus() was deprecated in iOS 14.0

To solve this, use the following:

private let locationManager = CLLocationManager()

if CLLocationManager.locationServicesEnabled() {
    switch locationManager.authorizationStatus {
        case .notDetermined, .restricted, .denied:
            print("No access")
        case .authorizedAlways, .authorizedWhenInUse:
            print("Access")
        @unknown default:
            break
    }
} else {
    print("Location services are not enabled")
}

In objective-c

you should track user already denied or not determined then ask for permission or sent user to Setting app.

-(void)askEnableLocationService
{
   BOOL showAlertSetting = false;
   BOOL showInitLocation = false;

   if ([CLLocationManager locationServicesEnabled]) {

      switch ([CLLocationManager authorizationStatus]) {
        case kCLAuthorizationStatusDenied:
            showAlertSetting = true;
            NSLog(@"HH: kCLAuthorizationStatusDenied");
            break;
        case kCLAuthorizationStatusRestricted:
            showAlertSetting = true;
            NSLog(@"HH: kCLAuthorizationStatusRestricted");
            break;
        case kCLAuthorizationStatusAuthorizedAlways:
            showInitLocation = true;
            NSLog(@"HH: kCLAuthorizationStatusAuthorizedAlways");
            break;
        case kCLAuthorizationStatusAuthorizedWhenInUse:
            showInitLocation = true;
            NSLog(@"HH: kCLAuthorizationStatusAuthorizedWhenInUse");
            break;
        case kCLAuthorizationStatusNotDetermined:
            showInitLocation = true;
            NSLog(@"HH: kCLAuthorizationStatusNotDetermined");
            break;
        default:
            break;
      }
   } else {

      showAlertSetting = true;
      NSLog(@"HH: locationServicesDisabled");
  }

   if (showAlertSetting) {
       UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:nil message:@"Please enable location service for this app in ALLOW LOCATION ACCESS: Always, Go to Setting?" delegate:self cancelButtonTitle:@"No" otherButtonTitles:@"Open Setting", nil];
       alertView.tag = 199;
       [alertView show];
   }
   if (showInitLocation) {
       [self initLocationManager];
   }

}

Implement alertView Delegate then sent user to enable location service if already deny by user.

-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{

   if (alertView.tag == 199) {
       if (buttonIndex == 1) {
           [[UIApplication sharedApplication] openURL:[NSURL URLWithString:UIApplicationOpenSettingsURLString]];
       }
       return;
   }
}

Init Location Manager

-(void)initLocationManager{
   self.locationManager = [[CLLocationManager alloc] init];
   if([self.locationManager respondsToSelector:@selector(requestAlwaysAuthorization)]) {
       [self.locationManager requestAlwaysAuthorization];
   }
}

Please note kCLAuthorizationStatusAuthorizedAlways and kCLAuthorizationStatusAuthorizedWhenInUse is difference.