ViewModel

Base class for business logic with automatic lifecycle management.

class CounterViewModel extends ViewModel {
  late final count = state(0);
  void increment() => count.update((c) => c + 1);
}

When disposed: state holders dispose, subscriptions cancel, async tasks stop.

Structure

class ProfileViewModel extends ViewModel {
  final ProfileRepository _repo;

  ProfileViewModel(this._repo);

  late final profile = asyncState<Profile>();
  late final isEditing = state(false);

  void loadProfile(String id) => load(profile, () => _repo.getProfile(id));
  void toggleEdit() => isEditing.update((v) => !v);
}

Dependencies

Pass through constructor for explicit, testable dependencies:

class OrderViewModel extends ViewModel {
  final OrderRepository _repo;
  final PaymentService _payment;

  OrderViewModel(this._repo, this._payment);
}

State

// Sync state
late final count = state(0);
late final name = state('');

// Async state
late final user = asyncState<User>();
late final items = asyncState<List<Item>>();

Streams

// Bind directly
late final user = bind(repo.userStream, initial: null);

// Or subscribe manually
ChatViewModel(ChatRepository repo) {
  subscribe(repo.messagesStream, (msgs) => messages.value = msgs);
}

Async Operations

// launch() — returns Task for cancellation
_task = launch((cancellation) async {
  await cancellation.wait(_repo.save(data));
  isSaved.value = true;
});

// launchWith() — callbacks
launchWith(
  (cancellation) => cancellation.wait(_repo.delete(id)),
  onSuccess: (_) => isDeleted.value = true,
  onError: (e) => error.value = e.toString(),
);

// load() — updates AsyncStateHolder
load(user, () => _repo.getUser(id));

All cancel on dispose. See Task for debouncing patterns.

Custom Cleanup

@override
void dispose() {
  _controller.dispose();
  super.dispose();
}

Automatic Cleanup

Resource	On Dispose
state() / asyncState()	Disposed
bind() / bindAsync()	Cancelled, disposed
subscribe()	Cancelled
launch() / load()	Cancelled

ViewModel Granularity

Prefer one ViewModel per screen or feature:

// ✅ Good: Focused ViewModels
class TodoListViewModel extends ViewModel { ... }
class TodoDetailViewModel extends ViewModel { ... }
class TodoSearchViewModel extends ViewModel { ... }

// ❌ Avoid: God ViewModel
class TodosViewModel extends ViewModel {
  // list state, detail state, search state, settings...
}

Focused ViewModels are easier to test, reuse, and maintain. They also benefit from cleaner lifecycle management—each ViewModel disposes only when its specific feature is no longer needed.