Merge branch 'github/main'

pull/591/head^2
Automerger 2 years ago
commit f1ddef4df5

@ -23,12 +23,14 @@ import com.google.samples.apps.nowinandroid.core.data.util.SyncStatusMonitor
import com.google.samples.apps.nowinandroid.core.domain.GetFollowableTopicsUseCase
import com.google.samples.apps.nowinandroid.core.domain.GetUserNewsResourcesUseCase
import com.google.samples.apps.nowinandroid.core.domain.model.UserNewsResource
import com.google.samples.apps.nowinandroid.core.model.data.UserData
import com.google.samples.apps.nowinandroid.core.ui.NewsFeedUiState
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.distinctUntilChanged
import kotlinx.coroutines.flow.flatMapLatest
import kotlinx.coroutines.flow.flowOf
import kotlinx.coroutines.flow.map
@ -40,7 +42,7 @@ import javax.inject.Inject
class ForYouViewModel @Inject constructor(
syncStatusMonitor: SyncStatusMonitor,
private val userDataRepository: UserDataRepository,
private val getSaveableNewsResources: GetUserNewsResourcesUseCase,
getUserNewsResources: GetUserNewsResourcesUseCase,
getFollowableTopics: GetFollowableTopicsUseCase,
) : ViewModel() {
@ -55,26 +57,8 @@ class ForYouViewModel @Inject constructor(
)
val feedState: StateFlow<NewsFeedUiState> =
userDataRepository.userData
.map { userData ->
// If the user hasn't completed the onboarding and hasn't selected any interests
// show an empty news list to clearly demonstrate that their selections affect the
// news articles they will see.
if (!userData.shouldHideOnboarding &&
userData.followedTopics.isEmpty()
) {
flowOf(NewsFeedUiState.Success(emptyList()))
} else {
getSaveableNewsResources(
filterTopicIds = userData.followedTopics,
)
.map<List<UserNewsResource>, NewsFeedUiState>(NewsFeedUiState::Success)
}
}
// Flatten the feed flows.
// As the selected topics and topic state changes, this will cancel the old feed
// monitoring and start the new one.
.flatMapLatest { it }
userDataRepository.getFollowedUserNewsResources(getUserNewsResources)
.map(NewsFeedUiState::Success)
.stateIn(
scope = viewModelScope,
started = SharingStarted.WhileSubscribed(5_000),
@ -116,3 +100,45 @@ class ForYouViewModel @Inject constructor(
}
}
}
/**
* Obtain a flow of user news resources whose topics match those the user is following.
*
* getUserNewsResources: The `UseCase` used to obtain the flow of user news resources.
*/
private fun UserDataRepository.getFollowedUserNewsResources(
getUserNewsResources: GetUserNewsResourcesUseCase,
): Flow<List<UserNewsResource>> = userData
// Map the user data into a set of followed topic IDs or null if we should return an empty list.
.map { userData ->
if (userData.shouldShowEmptyFeed()) {
null
} else {
userData.followedTopics
}
}
// Only emit a set of followed topic IDs if it's changed. This avoids calling potentially
// expensive operations (like setting up a new flow) when nothing has changed.
.distinctUntilChanged()
// getUserNewsResources returns a flow, so we have a flow inside a flow. flatMapLatest moves
// the inner flow (the one we want to return) to the outer flow and cancels any previous flows
// created by getUserNewsResources.
.flatMapLatest { followedTopics ->
if (followedTopics == null) {
flowOf(emptyList())
} else {
getUserNewsResources(filterTopicIds = followedTopics)
}
}
/**
* If the user hasn't completed the onboarding and hasn't selected any interests
* show an empty news list to clearly demonstrate that their selections affect the
* news articles they will see.
*
* Note: It should not be possible for the user to get into a state where the onboarding
* is not displayed AND they haven't followed any topics, however, this method is to safeguard
* against that scenario in future.
*/
private fun UserData.shouldShowEmptyFeed() =
!shouldHideOnboarding && followedTopics.isEmpty()

@ -60,6 +60,7 @@ class ForYouViewModelTest {
newsRepository = newsRepository,
userDataRepository = userDataRepository,
)
private val getFollowableTopicsUseCase = GetFollowableTopicsUseCase(
topicsRepository = topicsRepository,
userDataRepository = userDataRepository,
@ -71,7 +72,7 @@ class ForYouViewModelTest {
viewModel = ForYouViewModel(
syncStatusMonitor = syncStatusMonitor,
userDataRepository = userDataRepository,
getSaveableNewsResources = getUserNewsResourcesUseCase,
getUserNewsResources = getUserNewsResourcesUseCase,
getFollowableTopics = getFollowableTopicsUseCase,
)
}

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