Add Navigation Controllers to MainWindow_iPhone.xib and MainWindow_iPad.xib, and create a connection from the AppDelegate to the
Navigation Controller.
In the left pane, under the iPhone folder,
click the MainWindow_iPhone.xib file.
If you do not see the Navigation Controller in the middle pane, drag
it from Objects to the middle pane:
Under Objects in the middle pane, Ctrl-drag from the AppDelegate icon to the Navigation
Controller icon to create a navController outlet.
Click the expansion arrow at the bottom of the middle pane to switch to list
view, select Navigation Controller > View Controller, and in the Identity Inspector, select SubscribeController in the Class field.
Once the class is selected, the ViewController name in the hierarchy changes to
SubscribeController and the connection from the AppDelegate to the Navigation
Controller is created.
Repeat steps 1 – 3 to add a navigation controller to MainWindow_iPad.xib.