[JetNews] Implement SavedStateHandle for selectedPostId persistence

[xingarr]

Description

This PR addresses the TODO comment in HomeViewModel.kt by implementing SavedStateHandle to persist the selectedPostId across process death and configuration changes.

Problem

Previously, the selectedPostId was stored only in memory within HomeViewModelState. When Android's system killed the app process to reclaim memory (process death), this state would be lost, causing users to lose their selected article when returning to the app.

Solution

Implemented SavedStateHandle to persist the selectedPostId, following Android's recommended architecture patterns for state preservation.

Changes Made

HomeViewModel.kt

• ✅ Added SavedStateHandle as a constructor parameter
• ✅ Created StateFlow backed by SavedStateHandle for persistent storage
• ✅ Added observer to react to SavedStateHandle changes
• ✅ Simplified interactedWithArticleDetails() to directly save to SavedStateHandle
• ✅ Modernized ViewModel factory using viewModelFactory DSL
• ✅ Removed TODO comment

Key Implementation Details

// StateFlow backed by SavedStateHandle for persistence
private val selectedPostIdState: StateFlow<String?> = savedStateHandle.getStateFlow(
    key = SELECTED_POST_ID_KEY,
    initialValue = preSelectedPostId,
)

// Direct save to SavedStateHandle
fun interactedWithArticleDetails(postId: String) {
    savedStateHandle[SELECTED_POST_ID_KEY] = postId
}

[gemini-code-assist]

Summary of Changes

Hello @xingarr, 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 enhances the JetNews application by ensuring the selectedPostId state is reliably preserved across Android process deaths and configuration changes. By integrating SavedStateHandle into the HomeViewModel, the application prevents users from losing their selected article when the Android system reclaims memory or during device rotations, thereby providing a more robust and seamless user experience.

Highlights

• State Persistence: Implemented SavedStateHandle in HomeViewModel to persist selectedPostId across process death and configuration changes, addressing a previous TODO comment.
• Architecture Update: Modernized the HomeViewModel factory using the viewModelFactory DSL for improved dependency injection and lifecycle management.
• Code Refinement: Simplified the interactedWithArticleDetails function to directly update the SavedStateHandle, ensuring consistent state management.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request successfully implements SavedStateHandle to persist the selectedPostId, which is a great improvement for state preservation across process death. The modernization of the ViewModelProvider.Factory using the viewModelFactory DSL is also a welcome change that improves code clarity. However, I've found a significant bug in the implementation related to how the isArticleOpen state is handled. The current logic causes the article detail screen to be shown incorrectly after a configuration change or process restart, even if the user had navigated back to the feed. My review includes a detailed comment with a suggested fix to ensure the UI state is restored correctly.

[gemini-code-assist]

This collector introduces a bug where the UI state for isArticleOpen is not correctly restored after a configuration change or process death. By deriving isArticleOpen solely from selectedPostId != null, it incorrectly forces the article to be displayed even if the user had previously closed it and returned to the feed.

To fix this, the isArticleOpen state must also be persisted in SavedStateHandle. This requires a more comprehensive change across the ViewModel. Here's a step-by-step guide:

1. Define a new key for isArticleOpen in the companion object:

   private const val IS_ARTICLE_OPEN_KEY = "isArticleOpen"

2. Create a StateFlow for isArticleOpen from SavedStateHandle, right below selectedPostIdState:

   private val isArticleOpenState: StateFlow<Boolean> = savedStateHandle.getStateFlow(
       key = IS_ARTICLE_OPEN_KEY,
       initialValue = preSelectedPostId != null
   )

3. Update viewModelState initialization (around line 135) to use the new flow's value:

   private val viewModelState = MutableStateFlow(
       HomeViewModelState(
           isLoading = true,
           selectedPostId = selectedPostIdState.value,
           isArticleOpen = isArticleOpenState.value
       )
   )

4. Update interactedWithArticleDetails() (around line 237) to set both states in SavedStateHandle:

   fun interactedWithArticleDetails(postId: String) {
       savedStateHandle[SELECTED_POST_ID_KEY] = postId
       savedStateHandle[IS_ARTICLE_OPEN_KEY] = true
   }

5. Update interactedWithFeed() to also write to SavedStateHandle. Note: This function is not part of the PR changes, but it's a necessary part of the fix.

   fun interactedWithFeed() {
       savedStateHandle[IS_ARTICLE_OPEN_KEY] = false
   }

6. Replace this collector with two separate collectors, one for each state flow, to correctly update viewModelState.

        // Observe selectedPostId changes from SavedStateHandle
        viewModelScope.launch {
            selectedPostIdState.collect { selectedPostId ->
                viewModelState.update { it.copy(selectedPostId = selectedPostId) }
            }
        }

        // Observe isArticleOpen changes from SavedStateHandle
        viewModelScope.launch {
            isArticleOpenState.collect { isArticleOpen ->
                viewModelState.update { it.copy(isArticleOpen = isArticleOpen) }
            }
        }