flutter-logging

Flutter Logging

Full reference: template.md

Key rules

• AppLogger is the app-owned interface. Never import package:logger/logger.dart outside logger_impl.dart.
• Four log levels: debug, info, warn, error. All accept optional error and stackTrace params.
• LoggerImpl wraps the logger package. Configured with PrettyPrinter in dev/uat, SimplePrinter in prod.
• Logging is enabled based on AppConfig.enableLogging. Prod builds log only errors.
• Wire AppLogger into BlocObserver to log state transitions and errors automatically.
• Route observer (RouteObserver) logs page pushes/pops for screen tracking.
• Pass AppLogger via constructor injection — never resolve via getIt inside business logic.

AppBlocObserver pattern

Set in bootstrap — logs every cubit state change and routes all bloc errors to ErrorHandler:

class AppBlocObserver extends BlocObserver {
  AppBlocObserver({required AppLogger logger, required ErrorHandler errorHandler})
      : _logger = logger, _errorHandler = errorHandler;
  final AppLogger _logger;
  final ErrorHandler _errorHandler;

  @override
  void onError(BlocBase<dynamic> bloc, Object error, StackTrace stackTrace) {
    super.onError(bloc, error, stackTrace);
    _errorHandler.handleError(error, stackTrace, reason: '${bloc.runtimeType} error');
  }

  @override
  void onChange(BlocBase<dynamic> bloc, Change<dynamic> change) {
    super.onChange(bloc, change);
    _logger.debug('${bloc.runtimeType}: state → ${change.nextState.runtimeType}');
  }
}

Bootstrap wiring:

Bloc.observer = AppBlocObserver(
  logger: getIt<AppLogger>(),
  errorHandler: getIt<ErrorHandler>(),
);

Route observer

AppRouteObserver extends NavigatorObserver — logs screen pushes/pops. Wire into GoRouter observers:

final router = GoRouter(
  observers: [AppRouteObserver(logger: getIt<AppLogger>())],
);

Files

lib/src/core/logging/
  app_logger.dart          ← interface (debug / info / warn / error)
  logger_impl.dart         ← only file that imports package:logger
lib/src/core/bloc/
  app_bloc_observer.dart   ← logs BLoC state changes + routes errors to ErrorHandler
  app_route_observer.dart  ← logs screen push/pop via NavigatorObserver