Notes · iPhone Duo
A prompt for making iOS apps great on iPhone Duo
On the side, I build tools for athletes: fueling plans, swim workouts, indoor training, and most recently a forecast app for wind foilers.
Since the iPhone Duo is coming out, all of them needed an update: tabs in the new side bar, two columns when the phone is open, and new fold positions.
By hand first
I migrated them by hand, one round at a time: change something, check it folded, half open, fully open and held upright, and ask whether the second column actually helps or just fills space. I hit plenty of dead ends along the way.
Then one prompt
Once the apps were where I wanted them, I worked backwards and turned it all into one prompt: every tweak that worked, plus every shortcut that didn't and why, so a coding agent doesn't try them again.
It covers:
- Building with the iOS 27.1 SDK, without which the app runs letterboxed with no side bar.
- The vertical bar, using the system containers so tabs land in it.
- Two columns with
ArrangementView: what goes in each column, margins at the fold, one navigation bar over both, and opening a page beside the list. - Every pose: folded, half open like a book, flat, and held upright.
- What not to do: the shortcuts I tried that looked right and weren't.
- A checklist to verify each change on screen, and to check nothing changes on other iPhones.
Use it
Most iOS apps will need some version of this. If you're adapting yours, the prompt is on GitHub: github.com/nilsalb/iPhoneDuoPrompt.