Programmatically build / navigate a Navigation Controller

Question

Before:

My App is based on indepent view controllers. I can switch from one to another by replacing the root view controller on the application delegate:

Answer 1

Write the following code in AppDelegate.m Class

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
 {
   MainViewController *mainViewController = [[MainViewController alloc] initWithNibName:@"MainViewController" bundle:nil];
    self.nav = [[UINavigationController alloc] initWithRootViewController:mainViewController];
    self.nav.navigationBarHidden = YES;
    [mainViewController release];
   [_window addSubview:nav.view];
   [_window makeKeyAndVisible];
 }