How to get shared instance of location manger in synchronize - objective-c

Question

Hy, I want to get the background location updates, so I wrote the below code and make it synchronized to keep it safe from multithreading. So I have two questions:
Do I really need to synchronize the piece of code, all I am doing in App is just running background task? I never created any special NSThread type to support multithreading and don't require as such?
Whenever I need to start the location updates, I call like this:
CLLocationManager *locationManager = [LocationTracker sharedLocationManager];
locationManager.delegate = self;
[locationManager startUpdatingLocation];
Is correct way to call?
+ (CLLocationManager *)sharedLocationManager {
static CLLocationManager *_locationManager;
#synchronized(self) {
if (_locationManager == nil) {
_locationManager = [[CLLocationManager alloc] init];
_locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation;
[_locationManager requestAlwaysAuthorization];
_locationManager.distanceFilter = 10;
if(IS_OS_9_OR_LATER){
_locationManager.allowsBackgroundLocationUpdates = YES;
}
}
}
return _locationManager;
}

Answer 1

Shared instance should be synchronised. You can use #Synchronized or dispatch_once. It is good practice to synchronised the shared instances even you are not using the multiple threads.
+ (instancetype)sharedLocationManager {
static LocationTracker *sharedInstance_ = NULL;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedInstance_ = [[LocationTracker alloc] init];
[sharedInstance_ initialize];
});
return sharedInstance_;
}
- (void)initialize {
_locationManager = [[CLLocationManager alloc] init];
_locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation;
[_locationManager requestAlwaysAuthorization];
_locationManager.distanceFilter = 10;
if(IS_OS_9_OR_LATER){
_locationManager.allowsBackgroundLocationUpdates = YES;
}
}
You can implement the location manager delegates inside the LocationTracker class. Use NSNotificationObserver to update all the classes, which are all expecting location update.
Else follow the below line.
CLLocationManager *locationManager = [LocationTracker sharedLocationManager].locationManager;
locationManager.delegate = self;
[locationManager startUpdatingLocation];