Delay in Corelocation

Question

I've created a helper class for my location needs so i don't violate the DRY principle. The class looks like this:
Location.h

@interface Location : NSObject <CLLocationManagerDelegate>{
CLLocationManager *manager;
CLGeocoder *geocoder;
CLPlacemark *placemark;
}

-(float)latitude;
-(float)longitude;
-(NSString *)postalcode;

Location.m

@implementation Location{
    float latitude;
    float longitude;
    NSString *postalcode;
}
-(id)init{
    NSLog(@"Hallo");
    [self setupLocationManager];
    return self;
}

-(float)latitude{

    return latitude;
}

-(float)longitude{

    return longitude;
}

-(NSString *)postalcode{

    return postalcode;
}

-(void)setupLocationManager{
    manager = [[CLLocationManager alloc] init];
    [manager requestWhenInUseAuthorization];
    manager.delegate = self;
    manager.desiredAccuracy = kCLLocationAccuracyBest;
    manager.distanceFilter = 100;
    [manager startUpdatingLocation];
    geocoder = [[CLGeocoder alloc] init];
 }

 #pragma mark - CLLocationManagerDelegate Methods

 - (void)locationManager:(CLLocationManager *)manager didFailWithError:          (NSError *)error
{

     NSLog(@"Error: %@", error);
     NSLog(@"Failed to get location! :(");

}

 - (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{

NSLog(@"Location: %@", newLocation);
CLLocation *currentLocation = newLocation;

if (currentLocation != nil) {

    latitude = currentLocation.coordinate.latitude;
    longitude = currentLocation.coordinate.longitude;


}

[geocoder reverseGeocodeLocation:currentLocation completionHandler:^(NSArray *placemarks, NSError *error) {

    if (error == nil && [placemarks count] > 0) {

        placemark = [placemarks lastObject];
        postalcode = [NSString stringWithFormat:@"%@",placemark.postalCode];
        /*
         self.address.text = [NSString stringWithFormat:@"%@ %@\n%@ %@\n%@\n%@",
         placemark.subThoroughfare, placemark.thoroughfare,
         placemark.postalCode, placemark.locality,
         placemark.administrativeArea,
         placemark.country];
         */
    } else {

        NSLog(@"%@", error.debugDescription);

    }

} ];

}


 @end

When i in my ViewController tries to create an instance of Location and set latitude and longitude labels, in the viewDidLoad method, the labels are sat to 0.00000. Apparently it takes around half a second for Location to get the coordinates. I've tried using

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
        [self setCoordinateLabels];
    });

But that just seems very hacky and can't possibly be the best practise? So is there any way i could do this a better way?

Answer 1

Well - that is very hacky. Why don't you forward your delegate methods call?

locationManager:didUpdateToLocation:

(Btw. this is a legacy function)

Tells you when the first location is set. You can just have an array of delegates on your Location class and call every delegate when it's time.

Here is an example with blocks:

static NSMapTable *listenerBlocks;

+ (void)addListener:(NSObject *)listener listenerBlock:(void (^)())listenerBlock
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        listenerBlocks =
        [NSMapTable mapTableWithKeyOptions:NSMapTableWeakMemory
                              valueOptions:NSMapTableStrongMemory];
    });
    if (listenerBlock && listener) {
        [listenerBlocks setObject:listenerBlock forKey:listener];
    }
}

+ (void)removeListener:(NSObject *)listener
{
    if (listener) {
        [listenerBlocks removeObjectForKey:listener];
    }
}

In your locationManager:didUpdateToLocation: you then just call

NSArray *allBlocks = [[listenerBlocks objectEnumerator] allObjects];
for(void (^listenerBlock)(NSString *) in allBlocks)
{
    listenerBlock();
}

at the end

In the class that needs updates for the labels (e.g. myLabel):

[Location addListener:self listenerBlock:^{
   dispatch_async(dispatch_get_main_queue(),^{
      //myLabel.text = //... update your label here
      [self setCoordinateLabels]; // as from your code above..
   });
}];