When the view controller is presented within a tab bar controller, you can access the tab bar controller like this:
Swift
let tabBarController = viewController.tabBarController
Objective-C
UITabBarController *tabBarController = self.tabBarController;
When the view controller is part on an navigation stack, you can access the navigation controller like this:
Swift
let navigationController = viewController.navigationController
Objective-C
UINavigationController *navigationController = self.navigationController;