Mobile App UX — Platform Rules & Ergonomics

Bottom third of the screen = easy reach; top corners = hardest. On 6.1–6.9" phones, one-handed use dominates.
Primary actions, tab bars, key CTAs → bottom. Destructive actions → out of accidental-tap zones.
Top of screen: titles, status, search (with pull-down or bottom-sheet alternatives in reach-heavy apps).
FABs: bottom-right (Material); avoid covering list content actions.

Concern	iOS	Android
Back	Top-left back + edge-swipe	System back gesture/button — must always work correctly
Nav bar	Tab bar 49pt + safe area	Navigation bar 80dp
Typography	SF Pro, Dynamic Type	Roboto/brand, sp units
Sheets	Detent sheets, capsule buttons	Bottom sheets, M3 shapes
Settings	Grouped inset lists	Preference lists
Share/context	Share sheet, context menus (long-press preview)	Share sheet, ⋮ menus

Core brand and layout can match; navigation, gestures, pickers, and system integrations must be native-correct.

Every gesture needs a visible alternative (swipe-to-delete → edit mode / ⋯ menu).
Standard gestures only: swipe back, pull-to-refresh, long-press context, pinch zoom on media. Custom gestures need onboarding and rarely stick.
Don't fight system gestures: keep interactive elements out of edge-swipe zones and the home-indicator area.

Time-to-value is the metric: get users to the core "aha" in <60 seconds. Defer signup until value is shown when possible.
Skip intro carousels or cap at 3 screens with Skip; contextual education (tooltips at first encounter) beats upfront tours.
Personalization questions: only if answers visibly change the experience; show progress; ≤5 steps.
Permissions: ask in context with a pre-permission explainer screen (notifications after user does something worth notifying about — never on cold start). Each cold-start permission dialog costs conversions.
Sign-in: offer Apple/Google SSO first (one-tap), email fallback; passkeys are the 2026 default recommendation.

Cold start <2s to interactive content; show branded splash → skeleton, never splash → blank.
60fps scrolling is non-negotiable; janky lists read as "cheap app".
Offline: cache last content, queue writes, explicit offline banner + retry. Airplane-mode test every core flow.
Images progressive/lazy; interactions respond <100ms (optimistic UI for likes/saves).

Keyboard management: scroll focused input above keyboard; "Done/Next" return-key flow through forms; dismiss on scroll or tap-out.
Notifications: transactional > promotional; batch digests; deep-link every notification to its exact content.
App Store touchpoints: request review only after a success moment, cap frequency; never interrupt a task.
Haptics: light impact for selections/toggles, success/error notification haptics — subtle, never on scroll.
Text: minimum tap targets 44pt; body 16–17pt; support Dynamic Type up to accessibility sizes without truncation.

Web-view wrappers that ignore platform navigation.
Login wall before demonstrating any value (unless product truly requires it).
Interstitial ads/paywalls mid-task; notification permission dialog at first launch.
Hiding core actions behind long-press with no hint.
Splash screens >2s; forced app tours; blocking "rate us" dialogs.
Bottom sheets/keyboards covering the input being edited.

Sources