Get an iOS app ready for iPhone Duo

iPhone Duo is Apple's first foldable iPhone: a 5.4-inch outer display and a 7.6-inch inner display sharing one aspect ratio, joined by a hinge the user can leave at any angle. An existing iPhone app runs on it unchanged — but it will look like an app that has not been thought about.

This skill is the entry point. Work the checklist, then hand off to the specialist skill for whatever the app actually does.

The one idea to hold onto

iPhone Duo is not a new idiom. It is a wider continuum of sizes.

Every mistake in this port comes from an app asserting something fixed: this idiom, this orientation, this screen, this width, this symmetric inset. Every fix is the same shape — replace the assertion with a question about the space actually available right now.