newNavigationControl creates a NavigationControl widget.
A NavigationControl is a widget that switches between different views for you, giving the appearance of navigation. It creates its own NavBar widget to further aid in the navigation experience.
Its navigation is based on the concept of a "stack", where you push and pop items from the stack. In this case, an item is a page view in your app.
Pushing a new page will navigate forward to that page, and popping a page will navigate backward to the previous page.
When you create a view, you can assign a NavItem to that page, which will help fill out information in the NavBar when that page is showing. If a NavItem isn't supplied then one with default behavior is created automatically.
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