vnidrop/.codex/skills/compose-skill/references/navigation.md

Navigation

Shared navigation concepts for Nav 2 and Nav 3. Load first, then see version-specific references.

References:

• Nav 3 official docs
• Nav 2 official docs
• Kotlin CMP Nav 3 docs

Nav 2 vs Nav 3 Decision Guide

Criterion	Nav 3 (NavDisplay)	Nav 2 (NavHost / NavController)
Back stack ownership	You own it (SnapshotStateList)	Library owns it (NavController)
Navigation model	List manipulation — add(), removeLastOrNull()	Imperative — navigate(), popBackStack()
MVI alignment	Natural — back stack is state you mutate	Requires bridging — controller calls in effect handlers
Deep link parsing	You parse URIs, construct back stack manually	Built-in NavDeepLink parsing
Scenes / adaptive layouts	First-class: dialog, bottom sheet, list-detail	Manual: separate composable overlays
CMP support	Full (Android, iOS, Desktop, Web)	Android-only (JetBrains forks exist but differ)
Maturity	Newer — verify artifact stability for production	Stable, battle-tested
Fragment interop	None	Full Fragment/Activity integration

When to use Nav 3:

• New Compose projects following MVI architecture
• Compose Multiplatform projects targeting multiple platforms
• Projects wanting direct back stack control as state
• Projects needing adaptive layout scenes (list-detail, dialog, bottom sheet)

When to use Nav 2:

• Existing codebases already built on NavHost/NavController
• Projects requiring built-in deep link parsing via NavDeepLink
• Hybrid Compose + Fragment apps where Nav 2 provides Fragment integration
• Teams that prefer the declarative NavGraph DSL

Navigation in MVI

The architectural rule: ViewModels emit semantic effects; the route layer handles navigation. This rule applies identically to both Nav 2 and Nav 3.

sealed interface ItemEffect {
    data object NavigateBack : ItemEffect
    data class OpenDetails(val id: String) : ItemEffect
}

// Nav 3 route layer — manipulates back stack
CollectEffect(viewModel.effect) { effect ->
    when (effect) {
        is ItemEffect.NavigateBack -> backStack.removeLastOrNull()
        is ItemEffect.OpenDetails -> backStack.add(Details(effect.id))
    }
}

// Nav 2 route layer — calls NavController
CollectEffect(viewModel.effect) { effect ->
    when (effect) {
        is ItemEffect.NavigateBack -> navController.navigateUp()
        is ItemEffect.OpenDetails -> navController.navigate(Detail(effect.id))
    }
}

Rules

• Never call navigation during composition — always in LaunchedEffect or event handler callbacks
• Never pass the back stack (Nav 3) or NavController (Nav 2) to the ViewModel or leaf composables
• ViewModel emits semantic effects (NavigateBack, OpenDetails(id))
• Route/navigation layer translates effects to navigation calls
• Keep navigation logic at the route boundary, not in screens or leaves

Anti-Patterns

Anti-pattern	Applies to	Why it hurts	Better replacement
Navigating during composition	Both	Triggers on every recomposition, causes infinite loops	Navigate in LaunchedEffect or event handler callbacks
Passing NavController/back stack to ViewModel	Both	Violates MVI boundary, navigation becomes business logic	ViewModel emits semantic effects; route handles navigation
String-based routes without type safety	Both	No compile-time checking, argument mismatch at runtime	@Serializable data classes/objects
Missing onBack handler	Nav 3	System back gesture does nothing	Always provide onBack = { backStack.removeLastOrNull() }
Globally-scoped ViewModel for per-screen data	Both	Data leaks across screens, not cleared on pop	Entry-scoped VMs (Nav 3 decorators) or destination-scoped VMs (Nav 2)
Recreating back stacks on tab switch	Both	Loses user navigation history within tabs	Persistent per-tab stacks (Nav 3) or saveState/restoreState (Nav 2)
Missing entry decorators	Nav 3	ViewModels leak, saveable state lost	Always include both rememberSaveableStateHolderNavEntryDecorator and rememberViewModelStoreNavEntryDecorator
Using Nav 2 in new MVI codebases	Nav 3 preferred	Nav 3's user-owned back stack aligns better with MVI state ownership	Prefer Nav 3 NavDisplay for new MVI-first projects; Nav 2 remains valid for existing codebases

Version-Specific References

Load the file that matches your task:

• Nav 3 routes, tabs, scenes, deep links, or back stack patterns → navigation-3.md
• Nav 2 NavHost, tabs, deep links, nested graphs, or animations → navigation-2.md
• Wiring Hilt or Koin with Nav 3 → navigation-3-di.md
• Wiring Hilt or Koin with Nav 2 → navigation-2-di.md
• Migrating from Nav 2 to Nav 3 → navigation-migration.md