Adding a UITabBarController
Just as you did in Chapter 12 when adding navigation controllers, you will add the tab bar controller to the window directly in the app delegate.
The tab bar will manage two view controllers: the WebViewController and the SettingsViewController. To see how navigation controllers and tab bar controllers work together, you will wrap the SettingsViewController in a navigation controller. You can see how the tab bar organizes the views in the following image.
When combining tab bar controllers and navigation controllers, always put the tab bar controller at the root of the hierarchy.
To add the UITabBarController, ...