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Navigation architecture, deep links, and back stacks

Navigation is persisted application UI state, not a collection of button callbacks.

Typed routes and minimal arguments​

@Serializable data class OrderDetails(val orderId: String)

composable<OrderDetails> { entry ->
    val route = entry.toRoute<OrderDetails>()
    OrderRoute(orderId = OrderId(route.orderId))
}

Pass identifiers and reload authoritative data. Validate untrusted deep-link arguments and represent missing/unauthorized content.

Nested graph scope​

A checkout graph may share one flow ViewModel for address, delivery, review, and result. Scope it to the graph back-stack entry so it clears when the flow is removed—not to the Activity forever.

Multiple back stacks​

Bottom destinations often preserve an independent stack:

Home: Home -> Article
Search: Search -> Filters -> Result
Profile: Profile -> Settings

Define product behavior explicitly:

  • reselect top tab: pop to root or scroll to top?
  • back from secondary stack: within stack, switch home, or exit?
  • auth logout: clear protected stacks?
  • memory/process restoration: which entries and state return?

Authentication flow​

Do not sprinkle “if logged in navigate login” across destinations. Centralize access policy. Preserve a safe pending destination, authenticate, revalidate authorization, then navigate with stack-clearing rules that prevent returning to login or protected stale screens.

Treat URI as external input:

  1. parse/type-check
  2. normalize and reject ambiguous forms
  3. check auth/authorization
  4. load referenced data
  5. render not-found/offline/error states
  6. build meaningful Up/Back behavior

Never trust a deep link to grant access simply because a destination is reachable.

Results​

Small navigation results can use a previous back-stack entry's saved state. Important business outcomes belong in repository state so they survive process death and can be observed by any screen.

❌ Returning paymentSucceeded=true is the only truth.

✅ Order repository exposes accepted order status; navigation result may only prompt refresh/focus.

Navigation event duplication

Replayed state can navigate twice after recreation. Use an acknowledged transition or make navigation a deterministic consequence of durable state plus current destination.

Sources​

Interview exercises​

  1. Design logout stack clearing for three bottom tabs.
  2. Handle a deep link to an unauthorized/deleted order.
  3. Scope checkout state across nested destinations without Activity leakage.