How can I build an app with multiple types of controllers?

How can I accomplish the following:

1. When my app loads a UIView will show 4 buttons
2. Clicking on a button will load a UITabBarController (no开发者_运维问答t a UIView with a UITabBar) that can display multiple views.

This seems challenging to me, because in order for me to use the UITabBarController I need to add this to the window's subview in my appDelegate. By doing so, my app automatically will load with the UITabbarController in the root view.

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You don't need to add the UITabBarController in the application delegate, that's just the most common way to use it. You can have your initial view use a simple UIViewController, then when the button is pressed load the UITabBarController (either programmatically or from a nib), and then display it.

The following is an example of what might be in your app delegate:

- (BOOL) application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    
    // viewController is a UIViewController loaded from MainWindow.xib with a button that calls loadTabBarController
    [window addSubview:viewController.view];
    [window makeKeyAndVisible];

    return YES;
}

- (IBAction) loadTabBarController {
    self.tabBarController = [[[UITabBarController alloc] initWithNibName:@"MyTabBarController" bundle:nil] autorelease];
    [viewController.view removeFromSuperview];
    [window addSubview:tabBarController.view];
}