Swift version: 5.0
As of iOS 7.0, all views automatically go behind navigation bars, toolbars and tab bars to provide what Apple calls "context" – having some idea of what's underneath the UI (albeit blurred out with a frosted glass effect) gives users an idea of what else is just off screen.
If this is getting in your way (and honestly it does get in the way surprisingly often) you can easily disable it for a given view controller by modifying its
For example, if you don't want a view controller to go behind any bars, use this:
edgesForExtendedLayout = 
Available from iOS 7.0
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.