Trying to understand TabBarDelegate - objective-c

Question

In one of my ViewControllers I have the following code:
- (void)viewDidLoad
{
UITabBarController *tabBarController = (UITabBarController*)[UIApplication sharedApplication].keyWindow.rootViewController ;
[tabBarController setDelegate:self];
}
and :
- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController: (UIViewController*)viewController {
NSLog(#"Yup!");
}
Whenever I switch tabs in my multi-tab setup, the console spits out
Yup
just as expected.
However, when I add
UITabBarController *tabController = (UITabBarController*)self.window.rootViewController;
tabController.selectedIndex = 1;
to my AppDelegate.m's
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:
the 'Yup' doesn't show anymore.
How come?

Answer 1

didSelectViewController will call when you select/change tabs from the app itself, it will not call when you set the selectedIndex programmatically
tabController.selectedIndex = 1; , will mostly useful when you want to set default tab or want to change the selectedIndex programmatically
From apple doc:
- (void)tabBarController:(UITabBarController *)tabBarController
didSelectViewController:(UIViewController *)viewController
it is called only in response to user taps in the tab bar and is not
called when your code changes the tab bar contents programmatically.
You can try calling that method manually like this:
- (void) selectedItemWithIndex:(int)value {
tabbar.selectedIndex = value;
[self tabBarController:tabbar didSelectViewController:tabbar.viewControllers.firstObject];//place you vc here by array or manually
}
Ref: https://stackoverflow.com/a/30700712/4557505