PulseViewModel

abstract class PulseViewModel<
    UiState : PulseState,
    UiAction : PulseAction,
    Event : PulseEvent,
    Broadcast : PulseBroadcast,
    Unicast : PulseUnicast,
>(
    initialUiState: UiState,
    coroutineDispatcher: CoroutineDispatcher = Dispatchers.Default,
)

Abstract base class that holds the UI state of a content on the desktop, or of a screen on mobile.

The signature above is the desktop's, in mvi-desktop. In mvi-mobile the class takes three type parameters, and unicast, onReceive() and unicast() do not exist; everything else on this page is the same. Use unicast() on the desktop when the ViewModel needs to send messages up to its parent Container.

// mvi-mobile
abstract class PulseViewModel<
    UiState : PulseState,
    UiAction : PulseAction,
    Event : PulseEvent,
>(
    initialUiState: UiState,
    coroutineDispatcher: CoroutineDispatcher = Dispatchers.Default,
)

Properties

state

val state: StateFlow<UiState>

The current UI state as a hot, read-only StateFlow. Collecting it does not change the ViewModel lifecycle.

---

currentState

val currentState: UiState

Synchronous snapshot of the current UI state. Equivalent to state.value.

---

event

val event: Flow<Event>

A cold Flow of one-time side effects emitted via event(). Collected by PulseContent. Each event goes to a single collector and is consumed; it is not replayed to later collectors.

---

unicast

val unicast: SharedFlow<Unicast>

Desktop only. A hot stream of child-to-parent unicasts emitted via unicast().

---

coroutineScope

val coroutineScope: CoroutineScope

A CoroutineScope backed by SupervisorJob and the dispatcher passed to the constructor. The dispatcher defaults to Dispatchers.Default and can be swapped for Dispatchers.Main or a test dispatcher.

cancel() cancels this scope and replaces it with a fresh one.

Methods

onSetup()

open fun onSetup()

Called once, by PulseContent, the first time it observes the ViewModel. The instance outlives the composition, so leaving and re-entering it does not repeat the call.

Override it to start data-collection coroutines. They run in coroutineScope and stop when it is cancelled.

Observe an instance from one PulseContent at a time. event is a single-consumer channel, so a second observer would take events the first never sees.

---

onAction(uiAction)

abstract fun onAction(uiAction: UiAction)

Called each time the UI dispatches an action. Launch coroutines for async work here.

---

onReceive(broadcast)

open fun onReceive(broadcast: Broadcast)

Desktop only. Called when the parent PulseContainer delivers a broadcast. Default implementation does nothing.

---

update(block)

fun update(block: UiState.() -> UiState)

Applies an immutable state update. The lambda receives the current state as this and must return the next state:

update { copy(count = count + 1) }

---

event(effect)

fun event(effect: Event)

Emits a one-time side effect to the UI layer. Collected by the onEvent lambda in PulseContent.

Buffered, so it never suspends and keeps emission order.

Events emitted while no PulseContent is collecting — the destination is covered by another one, say — wait in the buffer and arrive when a collector returns. The buffer holds 64; beyond that, the oldest event is dropped.

---

unicast(unicast)

fun unicast(unicast: Unicast)

Desktop only. Emits a child-to-parent message. The parent PulseContainer collects the ViewModel's unicast flow and receives the message through onReceived().

---

cancel()

fun cancel()

Cancels the work started in onSetup() and replaces the scope with a fresh one, with the state preserved. The next PulseContent to observe the instance runs onSetup() again. Use it when the ViewModel may become active again.

---

close()

fun close()

Cancels the work started in onSetup() for good. Unlike cancel(), it does not replace the scope. onCleared() calls it when the owning ViewModelStore is cleared, so a discarded ViewModel cannot launch anything that outlives it.

Example

sealed class CounterUnicast : PulseUnicast {
    data object ResetRequested : CounterUnicast()
}

class CounterViewModel(
    private val repository: CounterRepository,
) : PulseViewModel<CounterState, CounterAction, CounterEvent, CounterBroadcast, CounterUnicast>(
    initialUiState = CounterState(),
) {
    override fun onSetup() {
        coroutineScope.launch {
            repository.count.collect { count ->
                update { copy(count = count) }
            }
        }
    }

    override fun onAction(uiAction: CounterAction) {
        coroutineScope.launch {
            when (uiAction) {
                CounterAction.Increment -> repository.increment()
                CounterAction.Decrement -> repository.decrement()
            }
        }
    }

    override fun onReceive(broadcast: CounterBroadcast) {
        when (broadcast) {
            CounterBroadcast.Reset -> update { CounterState() }
        }
    }
}

sealed class CounterUnicast : PulseUnicast {
    data object ResetRequested : CounterUnicast()
}

class CounterViewModel(
    private val repository: CounterRepository,
) : PulseViewModel<CounterState, CounterAction, CounterEvent, CounterBroadcast, CounterUnicast>(
    initialUiState = CounterState(),
) {
    override fun onAction(uiAction: CounterAction) {
        when (uiAction) {
            CounterAction.Reset -> {
                repository.reset()
                unicast(CounterUnicast.ResetRequested)
            }
            CounterAction.Increment -> repository.increment()
            CounterAction.Decrement -> repository.decrement()
        }
    }
}