ios - Please clear some confusions regarding UIViewController

Question

Please clear some confusions regarding UIViewController

I found this article Abusing UIViewController and here are the links link1 & link2

and summarised points

This is author's (and Apple’s) advice In a nutshell:

1. One (and only one) view controller should be responsible for a whole hierarchy (or screenful) of UIViews.
2. Mostly, you should only use one view controller per screen. Essentially the rootViewController of the current UIWindow should be the only UIViewController with a visible view.
3. Each different screen should have a different view controller i.e. one controller should not control more than one screen.
4. You should NOT nest custom UIViewControllers within a view hierarchy.
5. If more than one UIViewController hangs off the application’s UIWindow, only one of these will get the messages for changes in orientation. The other(s) will NOT get these messages.
6. Nested UIViewControllers are not guaranteed, or likely, to receive messages for changes in orientation or lifecycle messages such as viewDidAppear:, viewWillAppear:, viewDidDisappear: and viewWillDisappear: even though they inherit from UIViewController. Only the topmost UIViewController is certain to get these messages.

Please clear point number 2 and 3 because when we use UINavigationController or UITabBarController we use multiple subclasses of UIViewController. And ios device has only one screen.....

This article Abusing UIViewController highlight apple suggestion

Note: If you want to divide a view hierarchy into multiple subareas and manage each one separately, use generic controller objects (custom objects descending from NSObject) instead of view controller objects to manage each subarea. Then use a single view controller object to manage the generic controller objects.

and in apple docs under heading of Coordinating Efforts Between View Controllers apple saying

Few iOS apps show only a single screenful of content. Instead, they show some content when first launched and then show and hide other content in response to user actions. These transitions provide a single unified user interface that display a lot of content, just not all at once.....

My requirement is NOT to use any container or modal or popover, I want to do manual management, I have two view controllers VC1 & VC2. VC1 is the root view controller now I want to switch/transit/move to VC2 what should I do?

1. VC1 should be the only subclass of UIViewController and VC2 should be the subclass of NSObject to manage a particular view in VC1 hierarchy?(the show hide thing by apple doc).

2. VC2 can also be the subclass of UIViewController, I just remove VC1 from root view and add VC2 as root view?

or what is the correct way?

Answer 1

Container view controllers (like UINavigationController) allow working around the one-VC-per-screen rule. Since iOS 5, developers have been able and allowed to write our own container controllers (which aren't actually much different from normal VCs). Generally this means that writing non-VC controller objects is less necessary than it used to be.

In your situation, where you want to replace the root view controller, your option 2 makes more sense. Use VCs where you can, and non-VC controller objects only when you can't. Since you're replacing the whole screen's content, just switching the UIWindow rootViewController makes the most sense (edit: alternately, many devs would just use a navigation controller to present the second view, because it's simple and convenient).