Proper viewController setup for iPhone with login and logout functionality

In developing my current iPhone application, I'm having issues handling the login, logout functionality of presenting views.

I'd like to have my application have the following flow, but I cannot seem to figure out the proper viewcontroller setup:

When a user is not logged in, a login screen is immediately presented. Upon a successful login, the main application is displayed. The main application is a TabBarController. When returning back to the application, if you have already logged in, the login window will not display, but immediately go into the main tab bar. Once in the a开发者_StackOverflow中文版pp, you can "logout" and it will take you back to the login scren.

Please let me know if I need to go into further detail. There are a few other questions on here that are similar but not exactly what I'm looking for.

Thanks!

I would consider two ways of doing this:

have the login screen be a modal view controller that pops over the main UI. e.g. if (currentCredentials == nil) [self presentModalViewController:loginView animated:YES];

or alternately, handle switching between views using your app delegate.