ios device location course issue - ios

Question

I try to update device's location course real time.
I am doing some experiment, and i make the VC as CLLocationManager's delegate. But when i run the app, the course information is not updating at all. i did set up a breakpoint in the delegate setting line, but the location manager is nil from the debugging area.
What is the problem?
#import "CourseInfomationViewController.h"
#interface CourseInfomationViewController ()
- (IBAction)startMoveLocation:(id)sender;
#end
#implementation CourseInfomationViewController
{
CLLocationManager *_locationManager;
CLLocation *_deviceLocation;
double _deviceDirection;
double _altitude;
double _speed;
}
-(id)init {
if (self = [super init]) {
_locationManager = [[CLLocationManager alloc] init];
_locationManager.delegate = self;
_locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters;
//
_deviceLocation = [[CLLocation alloc] init];
}
return self;
}
- (IBAction)startMoveLocation:(id)sender {
[_locationManager startUpdatingLocation];
}
- (void)viewDidLoad {
[super viewDidLoad];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#pragma mark - location Delegate
- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray<CLLocation *> *)locations {
_deviceLocation = [locations lastObject];
_altitude = _deviceLocation.altitude;
_deviceDirection = _deviceLocation.course;
_speed = _deviceLocation.speed;
NSLog(#"altitude is %f", _altitude);
NSLog(#"altitude is %f", _deviceDirection);
NSLog(#"altitude is %f", _speed);
}
- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error {
NSLog(#"%#", error);
}