Initializes and returns a newly created navigation controller that uses your custom bar subclasses.
- iOS 5.0+
- tvOS 9.0+
The initialized navigation controller object or
nil if there was a problem initializing the object.
To customize the overall appearance of a navigation bar, use
UIAppearance APIs instead of this method. If you use this initialization method to create a navigation bar that uses custom bar subclasses, you are responsible for pushing and setting view controllers before presenting the navigation controller onscreen.