SwiftUI Size Classes for iPhone Duo: Build for Space, Not Device Names
A practical SwiftUI strategy using adaptive containers, size classes, ViewThatFits, AnyLayout, and stable state across display changes.
Start with system containers
Use NavigationStack and NavigationSplitView before building a custom two-pane shell. They understand compact and regular presentations and preserve expected platform behavior.
For smaller decisions, ViewThatFits can select a layout that fits. AnyLayout helps switch arrangements while preserving view identity. Keep model state above the adaptive branch so a layout change does not reset work.
Our ArrangementView guide covers reserved regions and our migration guide identifies legacy assumptions.
Test transitions, not screenshots
A layout can look correct in static previews and still lose focus, scroll position or typed text during transition. Test while editing, presenting a sheet, using large Dynamic Type and running Split View.
Avoid pose-driven structure
Hinge information can support an effect, but should not decide whether core navigation exists. Read why Apple discourages pose-driven design and our hinge API guide.
The target is not a special Duo layout. It is an app that remains coherent whenever its usable region changes. That improves iPad and future hardware too.
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Spotted something to fix, or an app we should cover?
This article is independent research, cross-checked against Apple's developer documentation. If something's out of date, or you know an app that deserves a look, let us know — and if you're building for iPhone Duo yourself, we're happy to talk.
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