setRootViewController: doesn't work as expected after setViewControllers: have been called - ios

Question

I created a view controller programmatically and set it as a root controller. All worked perfect as it was expected:
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
CustomViewController *vc = [[CustomViewController alloc] init];
[[self window] setRootViewController:vc];
self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];
return YES;
Then I added an UITabBarViewController, set its 'viewControllers' property to point to (an array to) the main viewController 'vc'.
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
CustomViewController *vc = [[CustomViewController alloc] init];
UITabBarController *tbc = [[UITabBarController alloc] init];
NSArray *controllers = #[vc];
[tbc setViewControllers:controllers];
[[self window] setRootViewController:vc];
self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];
return YES;
and the view stoped to show at the screen upon launch, also there is warning about the root view controller wasn't set. After adding the string below the view of 'vc' controller is finally loaded, but there is a blank line at the bottom of the screen, as if the UIBarController modified [[UIMainScreen bounds].
[[self window] addSubview:vc.view];
I'm new to iOS development, and I'm a bit confused. It seems I don't understand some very fundamental things about the view controllers hierarchy, but after reading the "View Controller Programming Guide" by Apple, I still don't understand where am I wrong.
The setRootViewController: method should auto assign the _view of argument view controller as default view of the window, but it doesn't happen if the named view controller was already previously pointed by viewControllers property of UITabBarViewController. Though I checked the debugger and found that 'vc' object isn't changed after setViewControllers: method is called.
Could you please explain me what is going on or point me to a documentation I should read?
UPDATE: I'm not going to insert the 'vc' controller into the 'tbc' controller. What I'd like is to display the 'vc' view fullscreen, as it would normally displayed without the code about 'tbc'.
From my point of view, adding another view (tbc in my case) should NOT affect this behaviour.
Of course, that's pretty useless from practical point of view, but I'd like to know what's going on under the hood.

Answer 1

You should set tbc as rootViewController.
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
CustomViewController *vc = [[CustomViewController alloc] init];
UITabBarController *tbc = [[UITabBarController alloc] init];
NSArray *controllers = #[vc];
[tbc setViewControllers:controllers];
[[self window] setRootViewController:tbc];
[[self window] addSubview:tbc.view];
self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];
return YES;

Answer 2

When you add vc to the tab bar controller, it becomes a child of that controller. The root view controller of the window can't be a child, which is why you get that error. If you want vc to be full screen, then don't put it in the tab bar controller, and then at some point, you switch the window's root view controller to be the tab bar controller (if that's what you want).
You haven't said what you want to use vc for. A better way, depending on its use, might be to present it modally (so it takes the whole screen) from whichever controller is in the first tab of your tab bar controller. Do this from viewDidAppear, and it will be the firsts thing the user sees when the app starts up.