UINavigationController: A container for view controllers that defines a method for navigating content based around a stack
The process
Setting up the UINavigationController subclasses
Where UINavigationController subclasses have been used is it required to create the subclass — for example GradientNavigationController is created through
File>New>File…
then creating a UINavigationController
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Which then, while using the Storyboard the subclass is chosen as in the following image