BaseViewModel<State, Event>

Abstract ViewModel base class providing typed state management, one-time events, and 5 async helpers.

Module: :ui-state

Definition

abstract class BaseViewModel<State, Event>(
    initialState: State
) : ViewModel()

Properties

Property	Type	Description
uiState	StateFlow<State>	Observable UI state
currentState	State	Current state snapshot
events	MutableEventFlow<Event>	One-time UI events

State Management

setState

Update state with a reducer function:

setState { copy(isLoading = true, error = null) }

The lambda receiver is the current state — use copy() for data classes.

sendEvent

Emit a one-time UI event:

sendEvent(MyEvent.ShowSnackbar("Item deleted"))
sendEvent(MyEvent.NavigateToDetail(itemId))

Async Helpers

collectResource

Pipes a one-shot suspend -> Resource<T> into a MutableStateFlow<Resource<T>>.

protected fun <T> collectResource(
    stateFlow: MutableStateFlow<Resource<T>>,
    call: suspend () -> Resource<T>
): Job

Example:

private val _users = MutableStateFlow<Resource<List<User>>>(Resource.Loading())
val users = _users.asStateFlow()

fun loadUsers() = collectResource(_users) { getUsersUseCase() }

---

collectFlow

Pipes a plain Flow<T> into a MutableStateFlow<Resource<T>>. Each emission is auto-wrapped in Resource.Success.

protected fun <T> collectFlow(
    stateFlow: MutableStateFlow<Resource<T>>,
    distinctUntilChanged: Boolean = false,
    flow: suspend () -> Flow<T>
): Job

Example:

private val _bookmarks = MutableStateFlow<Resource<List<Article>>>(Resource.Loading())
val bookmarks = _bookmarks.asStateFlow()

fun observe() = collectFlow(_bookmarks, distinctUntilChanged = true) {
    bookmarkDao.getAll() // Flow<List<Article>>
}

---

collectFlowResource

Pipes a Flow<Resource<T>> directly into a MutableStateFlow<Resource<T>>.

protected fun <T> collectFlowResource(
    stateFlow: MutableStateFlow<Resource<T>>,
    distinctUntilChanged: Boolean = false,
    flow: suspend () -> Flow<Resource<T>>
): Job

Example:

private val _feed = MutableStateFlow<Resource<List<FeedItem>>>(Resource.Loading())
val feed = _feed.asStateFlow()

fun observe() = collectFlowResource(_feed) {
    liveFeedUseCase() // Flow<Resource<List<FeedItem>>>
}

---

execute

One-shot suspend call with state reducers for full control:

protected fun <T> execute(
    call: suspend () -> Resource<T>,
    onLoading: (State.() -> State)? = null,
    onSuccess: State.(T) -> State,
    onError: (State.(AppException) -> State)? = null,
    errorEvent: ((AppException) -> Event)? = null
): Job

Parameters:

Parameter	Type	Description
call	suspend () -> Resource<T>	The async operation
onLoading	(State.() -> State)?	State reducer for loading state
onSuccess	State.(T) -> State	State reducer for success (required)
onError	(State.(AppException) -> State)?	State reducer for error
errorEvent	((AppException) -> Event)?	Emit an event on error

Example:

fun loadProducts() = execute(
    call = { getProductsUseCase() },
    onLoading = { copy(isLoading = true) },
    onSuccess = { copy(products = it, isLoading = false) },
    onError = { copy(error = it.message, isLoading = false) },
    errorEvent = { ProductEvent.ShowError(it.message ?: "Failed") }
)

---

collect

Reactive stream with state reducers:

protected fun <T> collect(
    flow: () -> Flow<Resource<T>>,
    distinctUntilChanged: Boolean = false,
    onLoading: (State.() -> State)? = null,
    onSuccess: State.(T) -> State,
    onError: (State.(AppException) -> State)? = null,
    errorEvent: ((AppException) -> Event)? = null
): Job

Example:

fun observeBookmarks() = collect(
    flow = { observeBookmarksUseCase() },
    distinctUntilChanged = true,
    onSuccess = { copy(bookmarks = it, isLoading = false) }
)

Decision Matrix

Need	Use
Simplest possible — one Resource drives the UI	collectResource
Observe a Room/DataStore Flow	collectFlow
Observe a Flow that already emits Resource	collectFlowResource
One-shot call, need to update multiple state fields	execute
Stream, need to update multiple state fields	collect