I have an iOS 5 era app that I need to update to "modern" terms to be able to submit an update to the app store. I am shooting for iOS 8 as a baseline using auto layout and size classes.
The base UI is a Tab Bar controller, each tab of which has a UINavigationController as its base.
MainWindow.xib is the main nib file used when opening the app.
I opened all the nibs and checked Use Autolayout and Use Size Classes.
The app runs, but always comes up as a 3.5" phone sized app, even on a 6 Plus (device or simulator). I cannot find any constraints applicable nor any settings in any of the nibs that seem to affect this.
The Tab Bar itself seems stuck at the 3.5" size and I can find no constraints or settings on this. The window and tab bar element themselves in the nib show the generic 600x600 / any-any size.
You need to add launch images for each device size you want to support. That tells iOS that the app actually can be displayed at that size and resolution.
Additionally you will want to add @3x assets for the iPhone 6+.