SwiftUI Patterns

Quick Start

Choose a track based on your goal:

Existing project

• Identify the feature or scene and the primary interaction model: document, editor, sidebar-detail, utility window, settings, or menu bar extra.
• Read the nearest existing scene or root view before inventing a new desktop structure.
• Choose the relevant reference from references/components-index.md.
• If SwiftUI cannot express the required platform behavior cleanly, use the appkit-interop skill rather than forcing a shaky workaround.

New app scaffolding

• Choose the scene model first: WindowGroup, Window, Settings, MenuBarExtra, or DocumentGroup.
• If the app combines a normal main window and a MenuBarExtra, use WindowGroup(..., id:) for the primary window when it should appear at launch. Treat Window(...) as a better fit for auxiliary/on-demand singleton windows; in menu-bar-heavy apps, a Window(...) scene may not present the main window automatically at launch.
• Before creating the scaffold, check whether the workspace is already inside a git repo with git rev-parse --is-inside-work-tree. If not, run git init at the project root so Codex app git-backed features are available from the start. Do not initialize a nested repo inside an existing parent checkout.
• For a new app scaffold, also create one project-local script/build_and_run.sh and .codex/environments/environment.toml so the Codex app Run button works immediately. Use the exact bootstrap contract from build-run-debug and its references/run-button-bootstrap.md file rather than inventing a second variant here.
• Decide which state is app-wide, scene-scoped, or window-scoped before writing views.
• Sketch file and module boundaries before writing the full UI. For any non-trivial app, create the folder structure first and split files by responsibility from the start.
• Use a single Swift file only for tiny throwaway examples or snippets: roughly under 50 lines, one screen, no persistence, no networking/process client, and no reusable models. Anything beyond that should be multi-file immediately.
• Use system-adaptive colors and materials by default (Color.primary, Color.secondary, semantic foreground styles, .regularMaterial, etc.) so the app follows Light/Dark mode automatically. Do not hardcode white or light backgrounds unless the user explicitly asks for a fixed theme, and do not reach for opaque windowBackgroundColor fills for root panes by default.
• Pick the references for the first feature surface you need: windowing, commands, split layouts, or settings.

New App File Structure

For any non-trivial macOS app, start with this shape instead of putting the app, all views, models, stores, services, and helpers in one Swift file:

• App/<AppName>App.swift: the @main app type and AppDelegate only.
• Views/ContentView.swift: root layout and high-level composition only.
• Views/SidebarView.swift, Views/DetailView.swift, Views/ComposerView.swift, etc.: feature views named after their primary type.
• Models/*.swift: value models, identifiers, and selection enums.
• Stores/*.swift: persistence and state stores.
• Services/*.swift: app-server, network, process, or platform clients.
• Support/*.swift: small formatters, resolvers, extensions, and glue helpers.

Keep files small and named after the primary type they contain. If a file starts collecting unrelated views, models, stores, networking clients, and helper extensions, split it before adding more behavior.

Pre-Edit Checklist For New App Scaffolds

Before writing the full UI:

1. Choose the scene model.
2. Choose state ownership: app-wide, scene-scoped, window-scoped, or view-local.
3. Sketch file and module boundaries.
4. Create the folder structure before filling in the UI.
5. Keep script/build_and_run.sh and .codex/environments/environment.toml separate from app source.

General Rules To Follow

• Design for pointer, keyboard, menus, and multiple windows.
• Keep scenes explicit. A separate settings window, utility window, or menu bar extra should be modeled as its own scene, not hidden inside one monolithic ContentView.
• Prefer system desktop affordances: commands, toolbars, sidebars, inspectors, contextual menus, and searchable.
• For menu bar apps, keep MenuBarExtra item titles and action labels short and scannable. Cap visible menu item text at 30 characters; if source content is longer, truncate or summarize it before rendering and open the full content in a dedicated window or detail surface.
• If a MenuBarExtra app should still behave like a regular Dock app with a visible main window/process, install an NSApplicationDelegate via @NSApplicationDelegateAdaptor, call NSApp.setActivationPolicy(.regular) during launch, and activate the app with NSApp.activate(ignoringOtherApps: true). If the app is intentionally menu-bar-only, document that .accessory / no-Dock behavior is a deliberate product choice.
• Prefer system-adaptive colors, materials, and semantic foreground styles. Avoid fixed white/light backgrounds in scaffolding and examples unless the requested design explicitly calls for a custom non-adaptive theme.
• Do not paint NavigationSplitView sidebars or root window panes with opaque custom Color(...) or Color(nsColor: .windowBackgroundColor) fills by default. Prefer native macOS sidebar/window materials and system-provided backgrounds unless the user explicitly asks for a custom opaque surface. In sidebar-detail-inspector layouts, let the sidebar keep the standard source-list/material appearance and reserve custom backgrounds for detail or inspector content cards where needed.
• Use @SceneStorage for per-window ephemeral state and @AppStorage for durable user preferences.
• Keep selection state explicit and stable. macOS layouts often pivot around sidebar selection rather than push navigation.
• Prefer NavigationSplitView or a deliberate manual split layout over iOS-style stacked flows when the app benefits from always-visible structure.
• For List(...).listStyle(.sidebar) and NavigationSplitView sidebars, prefer flat native rows with standard system selection/highlight behavior. Keep rows visually lightweight and Mail-like: at most one leading icon, one strong title line, and one optional secondary detail line in .secondary. Avoid stacked metadata rows, repeated inline utility icons, or dense multi-column status text in the sidebar. Reserve card-style and metadata-heavy surfaces for detail or inspector panes unless the user explicitly asks for a highly custom sidebar treatment.
• Keep primary actions discoverable from both UI chrome and keyboard shortcuts when appropriate.
• Use SwiftUI-native scenes and views first. If you need low-level window, responder-chain, text system, or panel control, switch to appkit-interop.

For concrete sidebar row and split-view background examples, read references/split-inspectors.md.

State Ownership Summary

Use the narrowest state tool that matches the ownership model:

Scenario	Preferred pattern
Local view or control state	@State
Child mutates parent-owned value state	@Binding
Root-owned reference model on macOS 14+	@State with an @Observable type
Child reads or mutates an injected @Observable model	Pass it explicitly as a stored property
Window-scoped ephemeral selection or expansion state	@SceneStorage when practical, otherwise scene-owned @State
Shared user preference	@AppStorage
Shared app service or configuration	@Environment(Type.self)
Legacy reference model on older targets	@StateObject at the owner and @ObservedObject when injected

Choose the ownership location first, then the wrapper. Do not turn simple desktop state into a view model by reflex.

Cross-Cutting References

• references/components-index.md: entry point for scene and component guidance.
• references/windowing.md: choosing between WindowGroup, Window, DocumentGroup, and window-opening patterns.
• references/settings.md: dedicated settings scenes, SettingsLink, and preference layouts.
• references/commands-menus.md: command menus, keyboard shortcuts, focused values, and desktop action routing.
• references/split-inspectors.md: sidebars, split views, selection-driven layout, and inspectors.
• references/menu-bar-extra.md: menu bar extra structure and when it fits.

Anti-Patterns

• One huge ContentView pretending the whole app is a single screen.
• A single Swift file containing the @main app, all views, models, stores, networking/process clients, formatters, and extensions. This is acceptable only for tiny throwaway snippets under the new-app threshold above.
• Touch-first interaction models ported directly from iOS without desktop affordances.
• Hiding core actions behind gestures with no menu, toolbar, or keyboard path.
• Building a menu-bar-plus-window app around only a Window(...) scene and then expecting the main window to appear at launch. Use WindowGroup(..., id:) for the primary launch window and reserve Window(...) for auxiliary/on-demand windows.
• Rendering full unbounded document titles, prompts, or message text directly inside a menu bar extra. Menu item labels should stay at or below 30 characters, with longer content moved into a dedicated window or detail view.
• Treating settings as another navigation destination in the main content window.
• Hardcoding .background(.white), Color.white, or a fixed light palette in a brand-new scaffold without an explicit design requirement.
• Wrapping each sidebar item in large rounded custom cards inside a .sidebar list, which fights native source-list density, alignment, and selection behavior unless the user explicitly asked for a bespoke visual sidebar.
• Building sidebar rows with multiple repeated icons, three or more text lines, or a dense strip of inline metadata counters/timestamps/models. Keep the sidebar row to one icon and one or two text lines, then move richer metadata into the detail pane.
• Painting NavigationSplitView sidebars or root window panes with opaque custom color fills by default, instead of letting the sidebar use native source-list/material appearance and reserving custom backgrounds for actual content cards.
• Using push navigation for layouts that want stable sidebar selection and detail panes.
• Reaching for AppKit before the SwiftUI scene and command APIs have been used properly.

Workflow For A New macOS Scene Or View

1. Define the scene type and ownership model before writing child views.
2. Decide which actions live in content, toolbars, commands, inspectors, or settings.
3. Sketch the selection model and layout: sidebar-detail, editor-inspector, document window, or utility window.
4. Create the file/folder structure for app entrypoint, root layout, feature views, models, stores, services, and support helpers.
5. Build with small, focused subviews and explicit inputs rather than giant computed fragments.
6. Add keyboard shortcuts and menu or toolbar exposure for actions that matter on desktop.
7. Validate the flow with a build and a quick usability pass: multiwindow assumptions, settings entry points, and selection stability.

Component References

Use references/components-index.md as the entry point. Each component reference should include:

• intent and best-fit scenarios
• minimal usage pattern with desktop conventions
• pitfalls and discoverability notes
• when to fall back to appkit-interop