ios - UIWindow's rootViewController considerations -

i've been reading several posts dealing switching rootviewcontroller of window, , said keeping same rootviewcontroller throughout app's lifecycle better switching it, , other posts related changing rootviewcontroller @ point of app. i'm confused this, , couldn't find recommendation regarding point in apple's docs.

what should best practice when have different content view controllers in app? example, let's have tabbed app (uitabbarcontroller) want first show welcome view signing in or signing (uinavigationcontroller):

1) approach fixed rootviewcontroller. think should set uitabbarcontroller rootviewcontroller, core of app tabbed, if user credentials needed, set uinavigationcontroller within uitabbarcontroller, hiding tab bar, push welcome view , navigate sign in/sign view controllers.

2) approach switching rootviewcontroller. firstly, if user credentials needed, set uinavigationcontroller rootviewcontroller show welcome view , navigate sign in/sign up, and, once user credentials provided or account created, switch rootviewcontroller uitabbarcontroller show core tabbed app.

in case best general approach switching rootviewcontroller needed, memory management considerations you'd take account? should need have 2 strong properties in appdelegate (uitabbarcontroller , uinavigationcontroller)? , transition between view controllers when switching rootviewcontroller: smooth, or should animate it?

thanks in advance

the approach of switching rootviewcontroller suits . firstly, if user credentials needed, set uinavigationcontroller rootviewcontroller show welcome view , navigate sign in/sign up, and, once user credentials provided or account created, switch rootviewcontroller uitabbarcontroller show core tabbed app

if store user credentials inside tabbarcontroller . store them in nsuserdefaults or plist in main bundle or created in document directory .