NavHost replaced with if statement

app/src/main/kotlin/com/google/samples/apps/nowinandroid/ui/interests2pane/InterestsListDetailScreen.kt

@@ -17,78 +17,41 @@
 package com.google.samples.apps.nowinandroid.ui.interests2pane
 
 import androidx.activity.compose.BackHandler
-import androidx.annotation.Keep
 import androidx.compose.material3.adaptive.ExperimentalMaterial3AdaptiveApi
-import androidx.compose.material3.adaptive.WindowAdaptiveInfo
-import androidx.compose.material3.adaptive.currentWindowAdaptiveInfo
 import androidx.compose.material3.adaptive.layout.AnimatedPane
 import androidx.compose.material3.adaptive.layout.ListDetailPaneScaffold
 import androidx.compose.material3.adaptive.layout.ListDetailPaneScaffoldRole
 import androidx.compose.material3.adaptive.layout.PaneAdaptedValue
 import androidx.compose.material3.adaptive.layout.ThreePaneScaffoldDestinationItem
-import androidx.compose.material3.adaptive.layout.calculatePaneScaffoldDirective
 import androidx.compose.material3.adaptive.navigation.ThreePaneScaffoldNavigator
 import androidx.compose.material3.adaptive.navigation.rememberListDetailPaneScaffoldNavigator
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
-import androidx.compose.runtime.key
-import androidx.compose.runtime.mutableStateOf
-import androidx.compose.runtime.remember
-import androidx.compose.runtime.saveable.Saver
-import androidx.compose.runtime.saveable.rememberSaveable
-import androidx.compose.runtime.setValue
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.navigation.NavGraphBuilder
-import androidx.navigation.compose.NavHost
 import androidx.navigation.compose.composable
-import androidx.navigation.compose.rememberNavController
 import com.google.samples.apps.nowinandroid.feature.interests.InterestsRoute
 import com.google.samples.apps.nowinandroid.feature.interests.navigation.InterestsRoute
 import com.google.samples.apps.nowinandroid.feature.topic.TopicDetailPlaceholder
-import com.google.samples.apps.nowinandroid.feature.topic.navigation.TopicRoute
-import com.google.samples.apps.nowinandroid.feature.topic.navigation.navigateToTopic
-import com.google.samples.apps.nowinandroid.feature.topic.navigation.topicScreen
-import kotlinx.serialization.Serializable
-import java.util.UUID
-
-@Serializable internal object TopicPlaceholderRoute
-
-// TODO: Remove @Keep when https://issuetracker.google.com/353898971 is fixed
-@Keep
-@Serializable internal object DetailPaneNavHostRoute
+import com.google.samples.apps.nowinandroid.feature.topic.TopicScreen
 
 fun NavGraphBuilder.interestsListDetailScreen() {
     composable<InterestsRoute> {
         InterestsListDetailScreen()
     }
 }
 
-@Composable
-internal fun InterestsListDetailScreen(
-    viewModel: Interests2PaneViewModel = hiltViewModel(),
-    windowAdaptiveInfo: WindowAdaptiveInfo = currentWindowAdaptiveInfo(),
-) {
-    val selectedTopicId by viewModel.selectedTopicId.collectAsStateWithLifecycle()
-    InterestsListDetailScreen(
-        selectedTopicId = selectedTopicId,
-        onTopicClick = viewModel::onTopicClick,
-        windowAdaptiveInfo = windowAdaptiveInfo,
-    )
-}
-
 @OptIn(ExperimentalMaterial3AdaptiveApi::class)
 @Composable
 internal fun InterestsListDetailScreen(
-    selectedTopicId: String?,
-    onTopicClick: (String) -> Unit,
-    windowAdaptiveInfo: WindowAdaptiveInfo,
+    viewModel: Interests2PaneViewModel = hiltViewModel()
 ) {
-    val listDetailNavigator = rememberListDetailPaneScaffoldNavigator(
-        scaffoldDirective = calculatePaneScaffoldDirective(windowAdaptiveInfo),
+    val selectedTopicId by viewModel.selectedTopicId.collectAsStateWithLifecycle()
+    val listDetailNavigator = rememberListDetailPaneScaffoldNavigator<String>(
         initialDestinationHistory = listOfNotNull(
             ThreePaneScaffoldDestinationItem(ListDetailPaneScaffoldRole.List),
-            ThreePaneScaffoldDestinationItem<Nothing>(ListDetailPaneScaffoldRole.Detail).takeIf {
+            ThreePaneScaffoldDestinationItem<String>(ListDetailPaneScaffoldRole.Detail).takeIf {
                 selectedTopicId != null
             },
         ),
@@ -97,33 +60,9 @@ internal fun InterestsListDetailScreen(
         listDetailNavigator.navigateBack()
     }
 
-    var nestedNavHostStartRoute by remember {
-        val route = selectedTopicId?.let { TopicRoute(id = it) } ?: TopicPlaceholderRoute
-        mutableStateOf(route)
-    }
-    var nestedNavKey by rememberSaveable(
-        stateSaver = Saver({ it.toString() }, UUID::fromString),
-    ) {
-        mutableStateOf(UUID.randomUUID())
-    }
-    val nestedNavController = key(nestedNavKey) {
-        rememberNavController()
-    }
-
-    fun onTopicClickShowDetailPane(topicId: String) {
-        onTopicClick(topicId)
-        if (listDetailNavigator.isDetailPaneVisible()) {
-            // If the detail pane was visible, then use the nestedNavController navigate call
-            // directly
-            nestedNavController.navigateToTopic(topicId) {
-                popUpTo<DetailPaneNavHostRoute>()
-            }
-        } else {
-            // Otherwise, recreate the NavHost entirely, and start at the new destination
-            nestedNavHostStartRoute = TopicRoute(id = topicId)
-            nestedNavKey = UUID.randomUUID()
-        }
-        listDetailNavigator.navigateTo(ListDetailPaneScaffoldRole.Detail)
+    fun onTopicClickShowDetailPane(selectedTopicId: String) {
+        viewModel.onTopicClick(selectedTopicId)
+        listDetailNavigator.navigateTo(ListDetailPaneScaffoldRole.Detail, selectedTopicId)
     }
 
     ListDetailPaneScaffold(
@@ -139,22 +78,15 @@ internal fun InterestsListDetailScreen(
         },
         detailPane = {
             AnimatedPane {
-                key(nestedNavKey) {
-                    NavHost(
-                        navController = nestedNavController,
-                        startDestination = nestedNavHostStartRoute,
-                        route = DetailPaneNavHostRoute::class,
-                    ) {
-                        topicScreen(
-                            showBackButton = !listDetailNavigator.isListPaneVisible(),
-                            onBackClick = listDetailNavigator::navigateBack,
-                            onTopicClick = ::onTopicClickShowDetailPane,
-                        )
-                        composable<TopicPlaceholderRoute> {
-                            TopicDetailPlaceholder()
-                        }
-                    }
-                }
+                if (selectedTopicId != null) {
+                    TopicScreen(
+                        topicId = selectedTopicId!!,
+                        showBackButton = !listDetailNavigator.isListPaneVisible(),
+                        onBackClick = listDetailNavigator::navigateBack,
+                        onTopicClick = ::onTopicClickShowDetailPane,
+                    )
+                } else
+                    TopicDetailPlaceholder()
             }
         },
     )

feature/foryou/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/foryou/ForYouScreen.kt

@@ -175,18 +175,6 @@ internal fun ForYouScreen(
                 onboardingUiState = onboardingUiState,
                 onTopicCheckedChanged = onTopicCheckedChanged,
                 saveFollowedTopics = saveFollowedTopics,
-                // Custom LayoutModifier to remove the enforced parent 16.dp contentPadding
-                // from the LazyVerticalGrid and enable edge-to-edge scrolling for this section
-                interestsItemModifier = Modifier.layout { measurable, constraints ->
-                    val placeable = measurable.measure(
-                        constraints.copy(
-                            maxWidth = constraints.maxWidth + 32.dp.roundToPx(),
-                        ),
-                    )
-                    layout(placeable.width, placeable.height) {
-                        placeable.place(0, 0)
-                    }
-                },
             )
 
             newsFeed(
@@ -258,17 +246,29 @@ private fun LazyStaggeredGridScope.onboarding(
     onboardingUiState: OnboardingUiState,
     onTopicCheckedChanged: (String, Boolean) -> Unit,
     saveFollowedTopics: () -> Unit,
-    interestsItemModifier: Modifier = Modifier,
 ) {
     when (onboardingUiState) {
         OnboardingUiState.Loading,
         OnboardingUiState.LoadFailed,
         OnboardingUiState.NotShown,
-        -> Unit
+            -> Unit
 
         is OnboardingUiState.Shown -> {
             item(span = StaggeredGridItemSpan.FullLine, contentType = "onboarding") {
-                Column(modifier = interestsItemModifier) {
+                // Custom LayoutModifier to remove the enforced parent 16.dp contentPadding
+                // from the LazyVerticalGrid and enable edge-to-edge scrolling for this section
+                Column(
+                    modifier = Modifier.layout { measurable, constraints ->
+                        val placeable = measurable.measure(
+                            constraints.copy(
+                                maxWidth = constraints.maxWidth + 32.dp.roundToPx(),
+                            ),
+                        )
+                        layout(placeable.width, placeable.height) {
+                            placeable.place(0, 0)
+                        }
+                    },
+                ) {
                     Text(
                         text = stringResource(R.string.feature_foryou_onboarding_guidance_title),
                         textAlign = TextAlign.Center,
@@ -493,7 +493,7 @@ private fun feedItemsSize(
         OnboardingUiState.Loading,
         OnboardingUiState.LoadFailed,
         OnboardingUiState.NotShown,
-        -> 0
+            -> 0
 
         is OnboardingUiState.Shown -> 1
     }

feature/topic/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/TopicScreen.kt

@@ -72,20 +72,24 @@ import com.google.samples.apps.nowinandroid.feature.topic.R.string
 
 @Composable
 fun TopicScreen(
+    topicId: String,
     showBackButton: Boolean,
     onBackClick: () -> Unit,
     onTopicClick: (String) -> Unit,
     modifier: Modifier = Modifier,
-    viewModel: TopicViewModel = hiltViewModel(),
+    viewModel: TopicViewModel = hiltViewModel()
 ) {
+    viewModel.updateTopic(topicId)
+
     val topicUiState: TopicUiState by viewModel.topicUiState.collectAsStateWithLifecycle()
     val newsUiState: NewsUiState by viewModel.newsUiState.collectAsStateWithLifecycle()
+    val selectedTopicId by viewModel.topicId.collectAsStateWithLifecycle()
 
-    TrackScreenViewEvent(screenName = "Topic: ${viewModel.topicId}")
+    TrackScreenViewEvent(screenName = "Topic: $selectedTopicId")
     TopicScreen(
         topicUiState = topicUiState,
         newsUiState = newsUiState,
-        modifier = modifier.testTag("topic:${viewModel.topicId}"),
+        modifier = modifier.testTag("topic:${selectedTopicId}"),
         showBackButton = showBackButton,
         onBackClick = onBackClick,
         onFollowClick = viewModel::followTopicToggle,

feature/topic/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/TopicViewModel.kt

@@ -16,10 +16,8 @@
 
 package com.google.samples.apps.nowinandroid.feature.topic
 
-import androidx.lifecycle.SavedStateHandle
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
-import androidx.navigation.toRoute
 import com.google.samples.apps.nowinandroid.core.data.repository.NewsResourceQuery
 import com.google.samples.apps.nowinandroid.core.data.repository.TopicsRepository
 import com.google.samples.apps.nowinandroid.core.data.repository.UserDataRepository
@@ -29,52 +27,74 @@ import com.google.samples.apps.nowinandroid.core.model.data.Topic
 import com.google.samples.apps.nowinandroid.core.model.data.UserNewsResource
 import com.google.samples.apps.nowinandroid.core.result.Result
 import com.google.samples.apps.nowinandroid.core.result.asResult
-import com.google.samples.apps.nowinandroid.feature.topic.navigation.TopicRoute
 import dagger.hilt.android.lifecycle.HiltViewModel
 import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.filterNotNull
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.stateIn
+import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import javax.inject.Inject
 
 @HiltViewModel
 class TopicViewModel @Inject constructor(
-    savedStateHandle: SavedStateHandle,
     private val userDataRepository: UserDataRepository,
     topicsRepository: TopicsRepository,
-    userNewsResourceRepository: UserNewsResourceRepository,
+    userNewsResourceRepository: UserNewsResourceRepository
 ) : ViewModel() {
 
-    val topicId = savedStateHandle.toRoute<TopicRoute>().id
+    private val _topicId = MutableStateFlow<String?>(null)
+    val topicId = _topicId.asStateFlow()
+
+    private val _topicUIState = MutableStateFlow<TopicUiState>(TopicUiState.Loading)
+
+    private val _newsUIState = MutableStateFlow<NewsUiState>(NewsUiState.Loading)
+
 
-    val topicUiState: StateFlow<TopicUiState> = topicUiState(
-        topicId = topicId,
-        userDataRepository = userDataRepository,
-        topicsRepository = topicsRepository,
+    init {
+        viewModelScope.launch {
+            _topicId.filterNotNull().collect { topicId ->
+                combine(
+                    topicUiState(
+                        topicId = topicId,
+                        userDataRepository = userDataRepository,
+                        topicsRepository = topicsRepository,
+                    ),
+                    newsUiState(
+                        topicId = topicId,
+                        userDataRepository = userDataRepository,
+                        userNewsResourceRepository = userNewsResourceRepository,
+                    ),
+                ) { topicIUState, newsUIState ->
+                    _topicUIState.update { topicIUState }
+                    _newsUIState.update { newsUIState }
+                }.stateIn(viewModelScope)
+            }
+        }
+    }
+
+    val topicUiState: StateFlow<TopicUiState> = _topicUIState.stateIn(
+        scope = viewModelScope,
+        started = SharingStarted.WhileSubscribed(5_000),
+        initialValue = TopicUiState.Loading,
     )
-        .stateIn(
-            scope = viewModelScope,
-            started = SharingStarted.WhileSubscribed(5_000),
-            initialValue = TopicUiState.Loading,
-        )
-
-    val newsUiState: StateFlow<NewsUiState> = newsUiState(
-        topicId = topicId,
-        userDataRepository = userDataRepository,
-        userNewsResourceRepository = userNewsResourceRepository,
+
+    val newsUiState: StateFlow<NewsUiState> = _newsUIState.stateIn(
+        scope = viewModelScope,
+        started = SharingStarted.WhileSubscribed(5_000),
+        initialValue = NewsUiState.Loading,
     )
-        .stateIn(
-            scope = viewModelScope,
-            started = SharingStarted.WhileSubscribed(5_000),
-            initialValue = NewsUiState.Loading,
-        )
 
     fun followTopicToggle(followed: Boolean) {
         viewModelScope.launch {
-            userDataRepository.setTopicIdFollowed(topicId, followed)
+            _topicId.value?.let {
+                userDataRepository.setTopicIdFollowed(it, followed)
+            }
         }
     }
 
@@ -89,6 +109,10 @@ class TopicViewModel @Inject constructor(
             userDataRepository.setNewsResourceViewed(newsResourceId, viewed)
         }
     }
+
+    fun updateTopic(id: String) {
+        this._topicId.value = id
+    }
 }
 
 private fun topicUiState(

feature/topic/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/topic/navigation/TopicNavigation.kt

@@ -36,8 +36,10 @@ fun NavGraphBuilder.topicScreen(
     onBackClick: () -> Unit,
     onTopicClick: (String) -> Unit,
 ) {
-    composable<TopicRoute> {
+    composable<TopicRoute> { entry ->
+        val id = entry.arguments?.getString("id")!!
         TopicScreen(
+            topicId = id,
             showBackButton = showBackButton,
             onBackClick = onBackClick,
             onTopicClick = onTopicClick,