iOS 9 on iPad introduces the ability to view and interact with more than one app at a time. Discover how to update your code to take advantage of enhancements to multitasking and how to participate in Slide Over and Split View. Learn specifics about how to architect your app and understand best practices for adapting to a dynamically sized interface.
AdaptivePhotos: Using UIKit Traits and Size Classes
WWDC 2015 > App Frameworks > Getting Started with Multitasking on iPad in iOS 9