IOS TabBarController Questions - uitabbarcontroller

Question

TabBar will be about 2 question. I am using a combination of a TabBar and NavigationController. As the following link.
http://developer.apple.com/library/ios/#featuredarticles/ViewControllerPGforiPhoneOS/CombiningViewControllers/CombiningViewControllers.html
Question 1:
I would like to appear before a TabBar to another ViewController. Several checks are here to do. (For example, Facebook login) If the prerequisites are met, tabbar will be visible. How do I do?
Question 2:
TabBar screen icon that appears in the middle of the first TabBar want it to be. The following code sequence also affects the order of TabBarItem.
self.tabBarController.viewControllers = [NSArray arrayWithObjects: viewController1, viewController2, nil];
Thank you.
Okan Sahin

Answer 1

For those who have the same problem:
I'm using Xcode 4.2. I have created Tabbed App.
Answer 1:
For loading screen,
I created a new ViewController.
AppDelegate.m
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
UIViewController *viewControllerLoading = [[LoadingViewController alloc] initWithNibName:#"LoadingViewController" bundle:nil];
self.window.rootViewController = viewControllerLoading;
[self.window makeKeyAndVisible];
return YES;
}
LoadingViewController.h
#interface LoadingViewController : UIViewController <UITabBarControllerDelegate>
#property (strong, nonatomic) UITabBarController *tabBarController;
#end
LoadingViewController.m
UIViewController *viewControllerFriends = [[FriendsViewController alloc] initWithNibName:#"FriendsViewController" bundle:nil];
UINavigationController* navController1 = [[UINavigationController alloc]
initWithRootViewController:viewControllerFriends];
UIViewController *viewConrollerMessages = [[MessagesViewController alloc] initWithNibName:#"MessagesViewController" bundle:nil];
UINavigationController* navController2 = [[UINavigationController alloc]
initWithRootViewController:viewConrollerMessages];
UIViewController *viewControllerWorld = [[WorldViewController alloc] initWithNibName:#"WorldViewController" bundle:nil];
UINavigationController* navController3 = [[UINavigationController alloc]
initWithRootViewController:viewControllerWorld];
UIViewController *viewControllerCheckIn = [[CheckInViewController alloc] initWithNibName:#"CheckinViewController" bundle:nil];
UINavigationController* navController4 = [[UINavigationController alloc]
initWithRootViewController:viewControllerCheckIn];
UIViewController *viewControllerProfile = [[ProfileViewController alloc] initWithNibName:#"ProfileViewController" bundle:nil];
UINavigationController* navController5 = [[UINavigationController alloc]
initWithRootViewController:viewControllerProfile];
self.tabBarController = [[UITabBarController alloc] init];
self.tabBarController.viewControllers = [NSArray arrayWithObjects:navController1, navController2, navController3, navController4, navController5, nil];
[self.view addSubview:self.tabBarController.view];
Answer 2:
self.tabBarController.selectedIndex = 2;
Best regards
Okan Sahin