Mobile UI Patterns

Mobile UI Patterns

Instructions

Mobile apps are built from a small set of recurring UI patterns. Using canonical patterns reduces design debt, makes navigation predictable, and keeps the codebase learnable. This skill names the patterns and shows the cross-platform equivalents.

1. The Core Pattern Set

2. The Tri-State Screen Contract

Every data-driven screen must handle loading, empty, and error as first-class states alongside content. Agents should reject "success-only" designs.

// SwiftUI
switch viewModel.state {
case .loading: ProgressView()
case .empty:   EmptyStateView(onAction: viewModel.createNew)
case .error(let e): ErrorStateView(message: e.localizedDescription, retry: viewModel.load)
case .content(let items): List(items) { ItemRow(item: $0) }
}

// Jetpack Compose
when (val s = state) {
    UiState.Loading -> CircularProgressIndicator()
    UiState.Empty   -> EmptyState(onAction = vm::createNew)
    is UiState.Error -> ErrorState(s.message, retry = vm::load)
    is UiState.Content -> LazyColumn { items(s.items) { ItemRow(it) } }
}

// Flutter
return switch (state) {
  Loading()            => const Center(child: CircularProgressIndicator()),
  Empty()              => EmptyState(onAction: vm.createNew),
  Error(:final message)=> ErrorState(message: message, retry: vm.load),
  Content(:final items)=> ListView(children: items.map(ItemRow.new).toList()),
};

// React Native
if (state.kind === 'loading') return <ActivityIndicator />;
if (state.kind === 'empty')   return <EmptyState />;
if (state.kind === 'error')   return <ErrorState message={state.message} retry={vm.load} />;
return <FlatList data={state.items} renderItem={({item}) => <ItemRow item={item} />} />;

3. List Pattern Details

• Use lazy containers: List, LazyColumn, ListView.builder, FlatList. Never map over an array of 1000 items into a non-virtualized container.
• Row height should be stable. If not, supply a key/id to aid diffing.
• Pull-to-refresh is expected on any user-owned list.
• Pagination is either cursor-based (preferred) or page-index-based, never both.
• Separator style follows platform: iOS inset separators, Android divider or none with spacing.

4. Detail Pattern Details

• Hero item is above the fold on phones.
• Primary action is a single, visually dominant button.
• Destructive actions go under an overflow menu or a confirmation sheet, never a primary button.
• On iOS, large navigation title collapses on scroll; on Android, use collapsing top app bar sparingly.

5. Tabs Pattern Details

• 2-5 tabs. Six is a code smell; replace with "More".
• Each tab owns its own navigation stack. Deep links restore into the right tab.
• Tab icons use filled/outlined variants for selected/unselected on both platforms.
• Do not hide tabs on scroll unless the screen is immersive (video, map).

6. Sheet Pattern Details

• Use sheets for tasks that could return the user to the previous context (composing, filtering).
• iOS 15+ supports presentationDetents([.medium, .large]); Android uses ModalBottomSheet.
• Avoid stacking sheets more than two deep.
• Sheets are dismissable with a swipe on both platforms; always persist draft state on dismiss.

7. Master-Detail Pattern Details

• Trigger breakpoint at 600-700 dp width (roughly iPad portrait, large foldable unfolded).
• On phones, this collapses to list -> detail push navigation.
• Preserve selection across orientation changes.
• Detail pane must function standalone (bookmarks, deep links land there directly).

8. Search Pattern Details

• Debounce input by 250-400 ms before querying.
• Cancel the previous request when a new one starts.
• Empty state shows recent searches or a helpful prompt.
• Respect the platform: search bar at top on Android (Material), inside navigation on iOS.

9. Form Pattern Details

• Keyboard type matches the field (.emailAddress, .numberPad, KeyboardType.Password, inputType, keyboardType="email-address").
• Focus advances on return; submit on the final field.
• Validate on blur, not on every keystroke.
• Show a single inline error per field, not a top-of-form summary alone.
• Forms must survive backgrounding and rotation without data loss.

10. Platform Convention Respect

Do not build a Material-styled app on iOS or vice versa. Conventions cost little at build time and dominate perceived quality. When using Flutter or React Native, use adaptive components (CupertinoSwitch / Switch, Platform.select) for controls that have strong platform semantics.

Checklist

• Every screen handles loading, empty, error, and content states explicitly.
• Lists use platform-appropriate lazy containers and keyed items.
• Tab count is 2-5; each tab has its own stack and deep-link entry.
• Sheets are used for sub-tasks, not primary navigation.
• Master-detail triggers on tablet-width; selection survives rotation.
• Search is debounced, cancellable, and has recent/empty states.
• Forms handle keyboard types, focus order, validation timing, and rotation.
• Platform controls are adaptive in cross-platform stacks.