[WIP] Add recipe to show Nav2 to Nav3 migration plan #46

dturner · 2025-07-16T11:47:28Z

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Summary of Changes

Hello @dturner, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new recipe to guide developers through the migration process from Android's Navigation 2 to Navigation 3. It sets up a foundational Navigation 2 example and then demonstrates the initial step of integrating Navigation 3 components while retaining the existing Navigation 2 structure.

Highlights

New Migration Recipe: Introduced a new 'recipe' to the project specifically designed to illustrate the migration path from Android's Navigation 2 to Navigation 3.
Incremental Migration Steps: Added two distinct MainActivity implementations (start and step1) to represent different stages of the migration. The start activity provides a basic Navigation 2 setup, while the step1 activity shows how to begin integrating Navigation 3's NavDisplay by bridging it with the existing Navigation 2 NavHost.
Dependency Management: Updated various Kotlin and serialization dependencies and explicitly added the Navigation 2 library to support the migration example.

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Code Review

This pull request introduces a new recipe to demonstrate a migration path from Navigation 2 to Navigation 3. It adds a 'start' state using Nav2 and a 'step1' state showing how to embed a Nav2 NavHost within a Nav3 NavDisplay.

The code is a good starting point, but I've identified a few areas for improvement:

There is a critical memory leak due to improper CoroutineScope usage in Nav3NavigatorSimple. I've provided suggestions to fix this using a lifecycle-aware scope from rememberCoroutineScope.
I've also suggested replacing a println call with standard Android logging and improving a brittle check on a class name for better maintainability.

gemini-code-assist · 2025-07-16T11:50:52Z

app/src/main/java/com/example/nav3recipes/migration/step1/MainActivity.kt

+        setEdgeToEdgeConfig()
+        super.onCreate(savedInstanceState)
+        setContent {
+            val navController = rememberNavController()


To ensure proper lifecycle management and prevent memory leaks, a CoroutineScope should be created using rememberCoroutineScope() and passed to Nav3NavigatorSimple. This scope is lifecycle-aware and will be cancelled when the composable leaves the composition. This declaration should precede the nav3Navigator initialization. Don't forget to add import androidx.compose.runtime.rememberCoroutineScope.

Suggested change

val navController = rememberNavController()

val coroutineScope = rememberCoroutineScope()

gemini-code-assist · 2025-07-16T11:50:52Z

app/src/main/java/com/example/nav3recipes/migration/step1/MainActivity.kt

+        super.onCreate(savedInstanceState)
+        setContent {
+            val navController = rememberNavController()
+            val nav3Navigator = remember { Nav3NavigatorSimple(navController) }


The Nav3NavigatorSimple should receive a lifecycle-aware CoroutineScope from its constructor to prevent memory leaks. This ensures that any coroutines launched within Nav3NavigatorSimple are properly cancelled when the MainActivity composable is disposed. This change is paired with the declaration of coroutineScope.

Suggested change

val nav3Navigator = remember { Nav3NavigatorSimple(navController) }

val nav3Navigator = remember { Nav3NavigatorSimple(navController, coroutineScope) }

gemini-code-assist · 2025-07-16T11:50:52Z

app/src/main/java/com/example/nav3recipes/migration/step1/MainActivity.kt

+class Nav3NavigatorSimple(val navController: NavHostController){
+
+    val coroutineScope = CoroutineScope(Job())


Using CoroutineScope(Job()) creates a scope that is not tied to any lifecycle, which causes memory leaks. The coroutine launched in init will never be cancelled. This class should receive a lifecycle-aware CoroutineScope from its creator (the MainActivity composable in this case) via its constructor. This change is paired with another one in MainActivity where the scope is created and passed.

Suggested change

class Nav3NavigatorSimple(val navController: NavHostController){

val coroutineScope = CoroutineScope(Job())

class Nav3NavigatorSimple(

val navController: NavHostController,

private val coroutineScope: CoroutineScope

) {

app/src/main/java/com/example/nav3recipes/migration/step1/MainActivity.kt

* main: Remove comments Add headings to the recipe picker Fix typo Add a recipe for creating dialogs. Add CODEOWNERS Add build workflow

* main: Update library versions Remove the extra blank line at end of CODEOWNERS file Update CODEOWNERS file

…tate through config changes

gemini-code-assist bot reviewed Jul 16, 2025

View reviewed changes

dturner added 13 commits July 21, 2025 15:16

Adding tests for Navigator

917a444

First draft of Navigator for nested and shared destinations

e88d470

Address AI feedback

1b9681c

Add Nav2 activity and dependencies

8a36488

Add starting point for migration

2104f89

Step 1 of migration complete

6a56eca

Lots of refactoring

24d2fb9

Add Step 4 of the migration

caed027

Add Step 5 of the migration

40482df

Part way through step 6 of migration

0110faa

Updating all steps

309f912

Add final step 7.

5019ac2

Tidy up imports

3e9bc63

dturner force-pushed the dt/2to3migration branch from 100d7e3 to 3e9bc63 Compare August 15, 2025 10:20

dturner added 6 commits August 15, 2025 11:22

Merge branch 'main' into dt/2to3migration

26f754d

* main: Remove comments Add headings to the recipe picker Fix typo Add a recipe for creating dialogs. Add CODEOWNERS Add build workflow

Merge branch 'main' into dt/2to3migration

0d9b38e

* main: Update library versions Remove the extra blank line at end of CODEOWNERS file Update CODEOWNERS file

Navigator uses SavedState APIs and KotlinX Serialization to persist s…

17b4015

…tate through config changes

Remove remaining Nav2 references from step 7

de6bdf4

Handle shared routes

466b3a1

Switch to using Saver

201f488

Provide feedback

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[WIP] Add recipe to show Nav2 to Nav3 migration plan #46

[WIP] Add recipe to show Nav2 to Nav3 migration plan #46

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	val navController = rememberNavController()
	val coroutineScope = rememberCoroutineScope()

	val nav3Navigator = remember { Nav3NavigatorSimple(navController) }
	val nav3Navigator = remember { Nav3NavigatorSimple(navController, coroutineScope) }

		class Nav3NavigatorSimple(val navController: NavHostController){

		val coroutineScope = CoroutineScope(Job())

[WIP] Add recipe to show Nav2 to Nav3 migration plan #46

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[WIP] Add recipe to show Nav2 to Nav3 migration plan #46

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dturner commented Jul 16, 2025

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Summary of Changes

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Code Review

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