UITabBar badge not updated - ios

Question

I can't seem to add a badge on a TabBarItem
Tried a lot of options (that's why the code is splitted into variables).
Thought it had something to do with the treading so the update is back on the main thread, still nothing.
The code:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSInteger badge_count = 0;
badge_count = getDataFromServer();
if (snacks_count > 0)
{
MainTabBarViewController *c = [self.storyboard instantiateViewControllerWithIdentifier:#"tabBarController"];
UINavigationController *nav = [c.viewControllers objectAtIndex:1];
dispatch_async(dispatch_get_main_queue(), ^{
nav.tabBarItem.badgeValue = [NSString stringWithFormat:#"%ld", (long)badge_count];
});
}
});

Answer 1

Please pay attention to the method: :instantiateViewControllerWithIdentifier" description:
Instantiates and returns the view controller with the specified identifier.
You use this method to create view controller objects that you want to manipulate and present programmatically in your application. Before you can use this method to retrieve a view controller, you must explicitly tag it with an appropriate identifier string in Interface Builder.
Namely, you create another instance.
You should change to
UINavigationController *nav = [self.viewControllers objectAtIndex:1];
in order to change the UINavigationController that you refer to

Answer 2

Apparently the original problem was that I didn't do it from the main thread. Probably made a wrong code with all the playing around trying to debug.
The working code:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
badge_count = getDataFromServer();
if (snacks_count > 0)
{
NSInteger badge_count = 0;
badge_count = getDataFromServer();
if (badge_count > 0)
{
dispatch_async(dispatch_get_main_queue(), ^{
[(UIViewController *)[self.tabBarController.viewControllers objectAtIndex:1] tabBarItem].badgeValue = [NSString stringWithFormat:#"%ld", (long)badge_count];
});
}
});