StackOverflow上有一个答案。
[CLLocationManager locationServicesEnabled]检测的是整个iOS系统的位置服务开关,无法检测当前应用是否被关闭,只能通过CLLocationManagerDelegate的locationManager:didFailWithError:方法去检测:
- (void)locationManager: (CLLocationManager *)manager
       didFailWithError: (NSError *)error {
    NSString *errorString;
    [manager stopUpdatingLocation];
    NSLog(@"Error: %@",[error localizedDescription]);
    switch([error code]) {
        case kCLErrorDenied:
            //Access denied by user
            errorString = @"Access to Location Services denied by user";
            //Do something...
            break;
        case kCLErrorLocationUnknown:
            //Probably temporary...
            errorString = @"Location data unavailable";
            //Do something else...
            break;
        default:
            errorString = @"An unknown error has occurred";
            break;
        }
    }
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:errorString delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil];
    [alert show];
    [alert release];
}
具体的CLError信息可以看CLLocationManager文档