What is Piper?

Lifecycle-aware ViewModels for Flutter with automatic cleanup.

class SearchViewModel extends ViewModel {
  final SearchRepository _repo;

  SearchViewModel(this._repo);

  late final results = asyncState<List<Result>>();
  Task<void>? _task;

  void search(String query) {
    _task?.cancel();
    _task = launch(() async {
      await Future.delayed(Duration(milliseconds: 300));
      results.setData(await _repo.search(query));  // Won't run if disposed
    });
  }
}

No "mounted" checks. No stream subscriptions to manage. No manual disposal.

Why Piper?

• Explicit dependencies — Constructor injection
• Automatic lifecycle — Subscriptions cancel, tasks stop, state disposes
• Plain Dart — Testable without Flutter
• Incremental — Works alongside existing solutions

Core Principles

Explicit over Magic

Dependencies are constructor parameters:

final vm = AuthViewModel(authRepository);

Lifecycle-Aware

When the ViewModel disposes, everything cleans up:

class AuthViewModel extends ViewModel {
  late final user = bind(repo.userStream, initial: null);
  void logout() => load(logoutState, () => repo.logout());
}

Plain Dart

Test without Flutter:

test('search', () async {
  final vm = SearchViewModel(mockRepo);
  vm.search('flutter');
  await Future.delayed(Duration(milliseconds: 300));
  expect(vm.results.hasData, isTrue);
});

Good Fit If You:

• Prefer constructor injection
• Want lifecycle management without ceremony
• Come from Android/iOS (familiar ViewModel patterns)
• Want testable business logic
• Are adopting incrementally

Next Steps

• Getting Started — Install and create your first ViewModel
• Core Concepts — StateHolder, AsyncState, and more
• Examples — Complete examples