flutter-conventions-index

Group code by feature folder, then by layer: View, ViewModel, Repository, Service. Lower layers never import upward, keeping the dependency graph a strict DAG. One Notifier per screen owns immutable state, and all mutations go through a repository's single write path.

Use modern Notifier, AsyncNotifier, Future, and Stream providers only, with providers doubling as the DI container. Avoid get_it, package:provider, and legacy StateProvider, StateNotifierProvider, or ChangeNotifierProvider to keep one composition model.

Return a sealed Result<T, F extends Failure> from recoverable I/O and switch on it exhaustively. Pure functions stay total and never throw, and failures carry a stable code rather than a localized string.

It assumes a single-package Flutter app by default. Monorepo and pub-workspace guidance lives inside the project-structure-and-packages and codegen-and-toolchain skills and is never required for a small app.

DateTime.now() is a non-deterministic global side effect that makes code untestable. Read the current time from an injected Clock interface instead, which can be faked in tests and overridden once at the composition root.

Methods stay at or under 30 lines, build() at or under 80 lines, files at or under 300 lines, with at most 3 positional parameters and 3 levels of logic nesting. Widget build trees may nest to 5 levels as the stated exception, and const StatelessWidget classes are extracted instead of _buildX() helpers.