refactor: extract stateInUi helper to reduce ViewModel boilerplate

Add FlowExtensions.kt in core:ui with a context(viewModel: ViewModel)
stateInUi() extension that wraps the standard stateIn() pattern used
across all ViewModels.

- core/ui: add FlowExtensions.kt with stateInUi()
- core/ui: add lifecycle-viewmodel-compose dependency
- build-logic: enable -Xcontext-parameters compiler flag
- app, feature/*: replace stateIn(...) calls with stateInUi()

Author: muraki-sports

app/src/main/kotlin/com/google/samples/apps/nowinandroid/MainActivityViewModel.kt

@@ -24,11 +24,10 @@ import com.google.samples.apps.nowinandroid.core.data.repository.UserDataReposit
 import com.google.samples.apps.nowinandroid.core.model.data.DarkThemeConfig
 import com.google.samples.apps.nowinandroid.core.model.data.ThemeBrand
 import com.google.samples.apps.nowinandroid.core.model.data.UserData
+import com.google.samples.apps.nowinandroid.core.ui.stateInUi
 import dagger.hilt.android.lifecycle.HiltViewModel
-import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.map
-import kotlinx.coroutines.flow.stateIn
 import javax.inject.Inject
 
 @HiltViewModel
@@ -37,11 +36,7 @@ class MainActivityViewModel @Inject constructor(
 ) : ViewModel() {
     val uiState: StateFlow<MainActivityUiState> = userDataRepository.userData.map {
         Success(it)
-    }.stateIn(
-        scope = viewModelScope,
-        initialValue = Loading,
-        started = SharingStarted.WhileSubscribed(5_000),
-    )
+    }.stateInUi(initialValue = Loading)
 }
 
 sealed interface MainActivityUiState {

build-logic/convention/src/main/kotlin/com/google/samples/apps/nowinandroid/KotlinAndroid.kt

@@ -105,5 +105,10 @@ private inline fun <reified T : KotlinBaseExtension> Project.configureKotlin() =
              */
             "-Xconsistent-data-class-copy-visibility",
         )
+        freeCompilerArgs.add(
+            // Enable context parameters (experimental, Kotlin 2.x).
+            // Used by Flow<T>.stateInUi which declares context(viewModel: ViewModel).
+            "-Xcontext-parameters",
+        )
     }
 }

core/ui/build.gradle.kts

@@ -30,6 +30,7 @@ dependencies {
     api(projects.core.model)
 
     implementation(libs.androidx.browser)
+    implementation(libs.androidx.lifecycle.viewModelCompose)
     implementation(libs.coil.kt)
     implementation(libs.coil.kt.compose)
 

core/ui/src/main/kotlin/com/google/samples/apps/nowinandroid/core/ui/FlowExtensions.kt

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.samples.apps.nowinandroid.core.ui
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.stateIn
+
+/**
+ * Converts a [Flow] to a [StateFlow] scoped to the [ViewModel]'s lifecycle, using
+ * [SharingStarted.WhileSubscribed] with a 5-second stop timeout.
+ *
+ * Shorthand for:
+ * ```
+ * stateIn(
+ *     scope = viewModelScope,
+ *     started = SharingStarted.WhileSubscribed(5_000),
+ *     initialValue = initialValue,
+ * )
+ * ```
+ *
+ * The [ViewModel] context is resolved implicitly from `this` when called inside a [ViewModel].
+ */
+context(viewModel: ViewModel)
+fun <T> Flow<T>.stateInUi(initialValue: T): StateFlow<T> = stateIn(
+    scope = viewModel.viewModelScope,
+    started = SharingStarted.WhileSubscribed(5_000),
+    initialValue = initialValue,
+)

feature/bookmarks/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/bookmarks/impl/BookmarksViewModel.kt

@@ -26,12 +26,11 @@ import com.google.samples.apps.nowinandroid.core.data.repository.UserNewsResourc
 import com.google.samples.apps.nowinandroid.core.model.data.UserNewsResource
 import com.google.samples.apps.nowinandroid.core.ui.NewsFeedUiState
 import com.google.samples.apps.nowinandroid.core.ui.NewsFeedUiState.Loading
+import com.google.samples.apps.nowinandroid.core.ui.stateInUi
 import dagger.hilt.android.lifecycle.HiltViewModel
-import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.flow.onStart
-import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import javax.inject.Inject
 
@@ -48,11 +47,7 @@ class BookmarksViewModel @Inject constructor(
         userNewsResourceRepository.observeAllBookmarked()
             .map<List<UserNewsResource>, NewsFeedUiState>(NewsFeedUiState::Success)
             .onStart { emit(Loading) }
-            .stateIn(
-                scope = viewModelScope,
-                started = SharingStarted.WhileSubscribed(5_000),
-                initialValue = Loading,
-            )
+            .stateInUi(initialValue = Loading)
 
     fun removeFromSavedResources(newsResourceId: String) {
         viewModelScope.launch {

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

@@ -29,15 +29,14 @@ import com.google.samples.apps.nowinandroid.core.data.util.SyncManager
 import com.google.samples.apps.nowinandroid.core.domain.GetFollowableTopicsUseCase
 import com.google.samples.apps.nowinandroid.core.notifications.DEEP_LINK_NEWS_RESOURCE_ID_KEY
 import com.google.samples.apps.nowinandroid.core.ui.NewsFeedUiState
+import com.google.samples.apps.nowinandroid.core.ui.stateInUi
 import dagger.hilt.android.lifecycle.HiltViewModel
 import kotlinx.coroutines.flow.Flow
-import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flowOf
 import kotlinx.coroutines.flow.map
-import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import javax.inject.Inject
 
@@ -70,27 +69,15 @@ class ForYouViewModel @Inject constructor(
             }
         }
         .map { it.firstOrNull() }
-        .stateIn(
-            scope = viewModelScope,
-            started = SharingStarted.WhileSubscribed(5_000),
-            initialValue = null,
-        )
+        .stateInUi(initialValue = null)
 
     val isSyncing = syncManager.isSyncing
-        .stateIn(
-            scope = viewModelScope,
-            started = SharingStarted.WhileSubscribed(5_000),
-            initialValue = false,
-        )
+        .stateInUi(initialValue = false)
 
     val feedState: StateFlow<NewsFeedUiState> =
         userNewsResourceRepository.observeAllForFollowedTopics()
             .map(NewsFeedUiState::Success)
-            .stateIn(
-                scope = viewModelScope,
-                started = SharingStarted.WhileSubscribed(5_000),
-                initialValue = NewsFeedUiState.Loading,
-            )
+            .stateInUi(initialValue = NewsFeedUiState.Loading)
 
     val onboardingUiState: StateFlow<OnboardingUiState> =
         combine(
@@ -103,11 +90,7 @@ class ForYouViewModel @Inject constructor(
                 OnboardingUiState.NotShown
             }
         }
-            .stateIn(
-                scope = viewModelScope,
-                started = SharingStarted.WhileSubscribed(5_000),
-                initialValue = OnboardingUiState.Loading,
-            )
+            .stateInUi(initialValue = OnboardingUiState.Loading)
 
     fun updateTopicSelection(topicId: String, isChecked: Boolean) {
         viewModelScope.launch {

feature/interests/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/interests/impl/InterestsViewModel.kt

@@ -24,14 +24,13 @@ import com.google.samples.apps.nowinandroid.core.domain.GetFollowableTopicsUseCa
 import com.google.samples.apps.nowinandroid.core.domain.TopicSortField
 import com.google.samples.apps.nowinandroid.core.model.data.FollowableTopic
 import com.google.samples.apps.nowinandroid.feature.interests.api.navigation.InterestsNavKey
+import com.google.samples.apps.nowinandroid.core.ui.stateInUi
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
 import dagger.hilt.android.lifecycle.HiltViewModel
-import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
-import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 
 @HiltViewModel(assistedFactory = InterestsViewModel.Factory::class)
@@ -57,11 +56,7 @@ class InterestsViewModel @AssistedInject constructor(
         selectedTopicId,
         getFollowableTopics(sortBy = TopicSortField.NAME),
         InterestsUiState::Interests,
-    ).stateIn(
-        scope = viewModelScope,
-        started = SharingStarted.WhileSubscribed(5_000),
-        initialValue = InterestsUiState.Loading,
-    )
+    ).stateInUi(initialValue = InterestsUiState.Loading)
 
     fun followTopic(followedTopicId: String, followed: Boolean) {
         viewModelScope.launch {

feature/search/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/search/impl/SearchViewModel.kt

@@ -28,14 +28,13 @@ import com.google.samples.apps.nowinandroid.core.data.repository.UserDataReposit
 import com.google.samples.apps.nowinandroid.core.domain.GetRecentSearchQueriesUseCase
 import com.google.samples.apps.nowinandroid.core.domain.GetSearchContentsUseCase
 import com.google.samples.apps.nowinandroid.core.model.data.UserSearchResult
+import com.google.samples.apps.nowinandroid.core.ui.stateInUi
 import dagger.hilt.android.lifecycle.HiltViewModel
-import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.catch
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flowOf
 import kotlinx.coroutines.flow.map
-import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import javax.inject.Inject
 
@@ -75,20 +74,12 @@ class SearchViewModel @Inject constructor(
                         }
                     }
                 }
-            }.stateIn(
-                scope = viewModelScope,
-                started = SharingStarted.WhileSubscribed(5_000),
-                initialValue = SearchResultUiState.Loading,
-            )
+            }.stateInUi(initialValue = SearchResultUiState.Loading)
 
     val recentSearchQueriesUiState: StateFlow<RecentSearchQueriesUiState> =
         recentSearchQueriesUseCase()
             .map(RecentSearchQueriesUiState::Success)
-            .stateIn(
-                scope = viewModelScope,
-                started = SharingStarted.WhileSubscribed(5_000),
-                initialValue = RecentSearchQueriesUiState.Loading,
-            )
+            .stateInUi(initialValue = RecentSearchQueriesUiState.Loading)
 
     fun onSearchQueryChanged(query: String) {
         savedStateHandle[SEARCH_QUERY] = query

feature/settings/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/settings/impl/SettingsViewModel.kt

@@ -23,14 +23,12 @@ import com.google.samples.apps.nowinandroid.core.model.data.DarkThemeConfig
 import com.google.samples.apps.nowinandroid.core.model.data.ThemeBrand
 import com.google.samples.apps.nowinandroid.feature.settings.impl.SettingsUiState.Loading
 import com.google.samples.apps.nowinandroid.feature.settings.impl.SettingsUiState.Success
+import com.google.samples.apps.nowinandroid.core.ui.stateInUi
 import dagger.hilt.android.lifecycle.HiltViewModel
-import kotlinx.coroutines.flow.SharingStarted.Companion.WhileSubscribed
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.map
-import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import javax.inject.Inject
-import kotlin.time.Duration.Companion.seconds
 
 @HiltViewModel
 class SettingsViewModel @Inject constructor(
@@ -47,11 +45,7 @@ class SettingsViewModel @Inject constructor(
                     ),
                 )
             }
-            .stateIn(
-                scope = viewModelScope,
-                started = WhileSubscribed(5.seconds.inWholeMilliseconds),
-                initialValue = Loading,
-            )
+            .stateInUi(initialValue = Loading)
 
     fun updateThemeBrand(themeBrand: ThemeBrand) {
         viewModelScope.launch {

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

@@ -27,16 +27,15 @@ import com.google.samples.apps.nowinandroid.core.data.repository.UserNewsResourc
 import com.google.samples.apps.nowinandroid.core.model.data.FollowableTopic
 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.ui.stateInUi
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
 import dagger.hilt.android.lifecycle.HiltViewModel
 import kotlinx.coroutines.flow.Flow
-import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.map
-import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 
 @HiltViewModel(assistedFactory = TopicViewModel.Factory::class)
@@ -51,22 +50,14 @@ class TopicViewModel @AssistedInject constructor(
         userDataRepository = userDataRepository,
         topicsRepository = topicsRepository,
     )
-        .stateIn(
-            scope = viewModelScope,
-            started = SharingStarted.WhileSubscribed(5_000),
-            initialValue = TopicUiState.Loading,
-        )
+        .stateInUi(initialValue = TopicUiState.Loading)
 
     val newsUiState: StateFlow<NewsUiState> = newsUiState(
         topicId = topicId,
         userDataRepository = userDataRepository,
         userNewsResourceRepository = userNewsResourceRepository,
     )
-        .stateIn(
-            scope = viewModelScope,
-            started = SharingStarted.WhileSubscribed(5_000),
-            initialValue = NewsUiState.Loading,
-        )
+        .stateInUi(initialValue = NewsUiState.Loading)
 
     fun followTopicToggle(followed: Boolean) {
         viewModelScope.launch {