UIViewController and UITabBARController

When I first launch the apps, I want it not to show the tab bar. Then after the user logins, it brings the tab bar. So how can I do this? Do I just hide the tab bar at first place then after the login succeed I will show 开发者_Python百科the tab bar or I should have a UITabBarController inside the UIViewController for the first time?

If you push a modal controller over the tab bar to do the login it will cover the tabs.

[self presentModalViewController:loginViewController animated:YES]