iOS Programming: Understand UINavigationController and the RootViewController

I'm reading Apple doc but I don't understand what a root controller is. The doc says that this is the controller at the bottom of the stack. Maybe, is this the controller that I've push the first time? Anyone can explain this concep开发者_如何学编程t?

From Apple doc UINavigationController, I've seen that there is a method called initWithRootViewController

Initializes and returns a newly created navigation controller. - (id)initWithRootViewController:(UIViewController *)rootViewController

What does it mean? Then, is it possible to change the root view controller or not?

Remember that rootViewController isn't a type of object, but a property name. It just happens to be the particular UIViewController instance at the bottom of the stack, as Nubbel said.

Methods like initWithRootViewController are for situations when you want to initialize UINavigationController, and also tell it to "use this VC as the first VC in the heirarchy".

It seems like UINavigationController really doesn't want you to change that property after it's been created, but it looks like ppl have found ways to do it: - Remember to check the comments to see if this is an "approved" method of working.

Just like the Docs and you already said, it is the controller at the bottom of the stack, the first controller pushed to the stack. Subsequent controllers will be pushed on top of the RootViewController. To return to the RootViewController you can use the popToRootViewControllerAnimated:method. Furthermore, you can't change the RootViewController!