iPhone Duo - your business app will need some TLC

Two screens, two layouts, one device. An everything product for everyone who can afford the buy-in. Fully open for a full cinematic experience, mostly open to read your favourite book, half-open for a Netflix and controls or that mini-laptop feel, text entry up top, keyboard on bottom, set like a tent for a night-stand and closed for a traditional, albeit somewhat chunky, iPhone experience.

As always, what makes this foldable different to offerings from the likes of Samsung et al, is the feels. With Apple, it’s always the feels. From the open/close blurring animations, to the app continuation between screens, to the speed, the weight, the thinness, the quality of the materials, the (almost) creaseless beautifully tactile screen, the smooth and snappy hinge, the hidden under-screen camera, they always seem to make a point to delight. And of course they’ve delighted.

From an app’s perspective we take some interesting turns. The closed screen is obviously shorter and wider than a traditional phone. Whilst this is unlikely to have a high impact, I’ve certainly worked on code recently that has had fixed floaters at the bottom of the screen that will not appreciate less height on the device, and suffer white-space issues with more width. Moving navigation and tab bar controls to the right side of the screen both inside and outside the device will change the equation in both cases, but designers are going to have to be on the ball; Liquid Glass controls on the right-hand side haven’t been seen before and are likely to require a mental shift.

Us devs are also going to need to adjust, being used to using vertical safe insets and layout margins, using horizontal versions definitely adds a new wrinkle, and many apps I’ve recently worked on will not be ready for this change. Portrait mode on the inner screen keeps the controls in their typical vertical positions, which should already be covered. It is worth mentioning that tab bar items that contain both icon and text will lose their text when shunted over to the right-hand vertical menu. Text-only items will stay, but a mix of vertical and horizontal input items will only be for the brave.

Something else that has been rather in vogue with recent codebases is custom-designed / developed sheets, alerts, popovers and menus. Companies understandably want to stand out, to add some brand identity into these UI elements. Liquid Glass made this somewhat more of a challenge; unfortunately, the Duo has the potential to make things even trickier, particularly on the inner screen. We’ve already mentioned the navigation, tool and tab bars heading to the right hand side, but the device can be half-closed making anything in the centre of the screen nigh-on impossible to interact with. I’ve been recommending companies use Apple’s APIs over heavy customisation for a long while, and this is a great example of where the benefits really do work out, with these system components automatically moving away from the centre line when the device folds. Yes, the app potentially loses some customisation, but gains significant usability and stability for the long-term.

The largest elephant in the room of course is the dynamic screen sizing. Apps will now need to be happy to run in a variety of configurations, with different combinations of compact and regular layouts depending on the screen open and its orientation. Some apps I’ve worked on recently have had this code built-in due to innate iPad support. iPhone-only apps are likely to be a bigger challenge, particularly older ones that never got the SwiftUI size class and UIKit trait collection updates. Supporting these size classes sets apps up nicely for the Duo’s screen complexities. And if you’re lucky enough to have a codebase that’s had a recent SwiftUI overhaul — the bulk of my work over the past couple of years — far less remedial work should be needed to get it running smoothly on a two-screen device.

On the other hand, fixed widths, fixed point sizes, fixed-pixel layouts (a lot of these exist, particularly the need to align vertical UI elements regardless of text line count), are most certainly on the table for updates.

So what does this all mean if you have apps on the App Store right now?

Well, if you’ve had a chance to migrate away from fixed device orientations and screen layouts, flows between the different Duo orientations should be seamless.  Moving away from custom UI elements and towards Apple’s standards will enable them to rotate and reposition smoothly, sliding away from the centre crease when the device folds, and heading to the location the UI deems most appropriate. Even better, if you’re lucky enough to have embraced SwiftUI as a standard, interfaces avoid safe areas naturally, and reserved regions can be dealt with quickly and easily. Custom tool and tab bars get slightly more challenging but once updated slide gracefully to the correct screen locations, overflowing into ellipsis overflow menus when space gets tight, keeping customisation available when desired. It’s beautiful, both what you see, and what is under the hood. And only a simple iOS 27.0 rebuild and resubmit is all it takes to get the journey started towards taking advantage of that stunning inner screen. Sure, more elephants above will need taming, but with pre-orders starting October 16th and deliveries coming a week later on the 23rd, you have plenty of time to get in touch. We will always be happy to offer advice where we can.

——

Apps should feel like a single experience between the two screens. Does yours? Need help / advice / support? You know where to find us.