ios - CLLocationManager never asks user about location services

I have an IOS 8-only app in which I want to use location services to obtain the device's latitude and longitude. I think I have everything implemented correctly, but the app never asks the user if it's okay to use location services, the CLAuthorizationStatus never changes from kCLAuthorizationStatusNotDetermined and the CLLocationManager delegate method

- (void)locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)newHeading 

never gets called.

Here's the CLLocationManager defined in the interface file for the viewcontroller:

__strong CLLocationManager *locationManager;

Here's the code in the viewcontroller:

- (void)viewDidLoad{
    [super viewDidLoad];


    locationManager = [[CLLocationManager alloc] init];
    locationManager.delegate = self;
    CLAuthorizationStatus status = [CLLocationManager authorizationStatus];
    if (status == kCLAuthorizationStatusNotDetermined) {
        [locationManager requestWhenInUseAuthorization];
    }
    [locationManager startUpdatingLocation];
    //... other viewDidLoad code
}

The Info.plist file for the app has an entry for NSLocationWhenInUseUsageDescription.

Debug tracing shows that the line

[locationManager requestWhenInUseAuthorization];

gets executed, but the dialog requesting the user to okay location services does not appear.

Location services in this app worked correctly under iOS 7 - I'm clearly doing something wrong, or not doing something I need to do to make it work in iOS 8. But I have dug around looking for insights, and it looks to me as if I'm doing everything correctly.

Any ideas and/or suggestions? Thanks in advance.