Apple iPhone Duo makes developers think in folds

The display’s contents automatically (and stylishly) move to the visible screen when the device is opened or snapped shut.  Apple has published a repository of technical documentation to help devs prepare for the new form factor. Who knows what other ways people, with their endless ingenuity, will interact with these gadgets.  Both screens have a 120 Hz adaptive refresh rate, thanks to Apple’s ProMotion technology. So any transitions within the app, and resizing of the app itself, need to be almost Walt Disney animation-level smooth - while maintaining state. The device can accommodate two apps simultaneously running on the screen, through “Split View,” so apps will also have to learn to share the screen nicely.  To address this new topology, Apple is updating its Xcode IDE; the 27.1 beta will be available later this month.  The backend will need some love too The iPhone Duo screen is a different world for a number of reasons. Size is no longer a value, but a dynamic range, Deosthale noted. An app’s available size needs to be read at layout time and adjusted through the app’s lifetime as its screen allocation changes.   Some apps will work better in this environment than others, Deosthale noted.  Apps with fixed layouts and hardcoded dimensions, or that use view controllers that reload on size change, can appear stretchy. “Those need work,” he wrote. Compared with the iPhone Pro Max, the Duo offers a bit more space, with a 7.6-inch inner display versus 6.9 inches. It’s wide enough that a single column stretching across the entire display won’t impress anyone. Now’s the chance to add in a detail pane or sidebar, side-by-side presenter and viewer modes, Deosthale suggested.  And don’t let the app just disappear features, data or other miscellanea when the user switches screens. That will just come off as cheesy. Snapping the unit shut mid-task means the app needs to preserve its state, along with the user’s session identity, as the interface moves to the outer display. Try not to move components around too much when the display switches, leaving the user seeking some option anew. In the technical docs, Apple calls this keeping a “consistent experience.” Contrary to the traditional iPhone layout, some of the device’s system controls have moved from the bottom toward the side of the display, which, in landscape mode, is a sensible change that leaves more, albeit asymmetrical, vertical space.