flutter-dart-patterns

Flutter Dart Patterns

Full reference: template.md

Key rules

Records for multi-value returns — no custom result classes

// DON'T — unnecessary class for a simple pair
class TaskPage {
  final List<Task> tasks;
  final bool hasMore;
  TaskPage({required this.tasks, required this.hasMore});
}

// DO — named record fields, destructurable at call sites
typedef TaskPage = ({List<Task> tasks, bool hasMore});

Future<TaskPage> call(({int page, int limit}) params) async {
  final dtos = await _remote.getTasks(page: params.page, limit: params.limit);
  return (tasks: dtos.map((d) => d.toEntity()).toList(), hasMore: dtos.length == params.limit);
}

// Call site — destructure inline
final (:tasks, :hasMore) = await getTasksUseCase((page: 1, limit: 20));

Sealed classes — exhaustive hierarchies for state and failures

// Cubit state — sealed for exhaustive switch in UI
sealed class TaskListState extends Equatable {
  const TaskListState();
}
final class TaskListInitial   extends TaskListState { ... }
final class TaskListLoading   extends TaskListState { ... }
final class TaskListLoaded    extends TaskListState { ... }
final class TaskListError     extends TaskListState { ... }

// UI — switch must cover all branches or compiler errors
return switch (state) {
  TaskListInitial()     => const SizedBox.shrink(),
  TaskListLoading()     => const AppShimmer(),
  TaskListLoaded(:final tasks, :final hasMore) => TaskListView(tasks: tasks),
  TaskListError(:final message) => AppErrorState(message: message),
};

Extension methods — add behavior to types you don't own

// DON'T — utility function scattered across files
String formatDate(DateTime dt) => DateFormat('MMM d, y').format(dt);

// DO — extension on the type itself
extension DateTimeX on DateTime {
  String get formatted => DateFormat('MMM d, y').format(this);
  bool get isToday => DateUtils.isSameDay(this, DateTime.now());
}

// BuildContext extensions reduce boilerplate
extension BuildContextX on BuildContext {
  ThemeData get theme => Theme.of(this);
  ColorScheme get colors => Theme.of(this).colorScheme;
  AppLocalizations get l10n => AppLocalizations.of(this)!;
  bool get isMobile => MediaQuery.sizeOf(this).width < 600;
}