iphone - navigating to a TabBar from different ViewControllers -

i trying build app has landing screen link either "signin" page or "sign up" page. meat of app tabbar. right place implement tabbarcontroller given user can have following flow:

1. landing page - >sign in -> main app
2. landing page - > sign -> main app
3. straight main app if user logged in already

is possible in appdelegate? then, how go appdelegate if @ "sign in"/"sign up" page?

thanks help!!

create modal view pop ups (the landing page) if user not signed in/up. once either sign in or sign up, dismiss view.

just create view , xib, , if first view load detects not logged in (example: have tab bar twitter feed, facebook feed, , feed, first view twitter view, senses aren't signed up/logged in awesome service, calls modal view sign in/up) once users done dismiss modal view.

here's official documentation: http://developer.apple.com/library/ios/#featuredarticles/viewcontrollerpgforiphoneos/modalviewcontrollers/modalviewcontrollers.html

   uinavigationcontroller *loginview = [[uinavigationcontroller alloc]init];     [self presentmodalviewcontroller:loginview animated:yes]; 

to dismiss (from within login view)

   [self dismissmodalviewcontrolleranimated:yes];