Error Handling

api_exceptions.dart

@immutable
class ApiException implements Exception {
  final String _message;
  final String _prefix;

  String get message => _message;

  const ApiException([this._message, this._prefix]);

  String toString() => "$_prefix$_message";
}

class FetchDataException extends ApiException {
  FetchDataException([String message])
      : super(message, "Error During Communication: ");
}

class BadRequestException extends ApiException {
  BadRequestException([message]) : super(message, "Invalid Request: ");
}

class UnauthorisedException extends ApiException {
  UnauthorisedException([message]) : super(message, "Unauthorised: ");
}

class InvalidInputException extends ApiException {
  InvalidInputException([String message]) : super(message, "Invalid Input: ");
}

base_state.dart

abstract class BaseState<T extends StatefulWidget> extends State<T> {
  final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();

  GlobalKey<ScaffoldState> get scaffoldKey => _scaffoldKey;

  BlocBase baseBloc;

  setBaseBloc(BlocBase baseBloc) {
    this.baseBloc = baseBloc;
    _listenToErrors();
  }

  _listenToErrors() {
    baseBloc?.baseError?.listen((e) {
      _showSnackBar(e.exception);
    });
  }

  _showSnackBar(Exception exception) {
    _scaffoldKey.currentState.hideCurrentSnackBar();
    _scaffoldKey.currentState
        .showSnackBar(SnackBar(content: Text('$exception')));
  }
}

bloc_base.dart

abstract class BlocBase {
  final _prefHelper = locator<AppPreferencesHelper>();

  final _subjectBaseError = BehaviorSubject<CaughtException>();

  Observable<CaughtException> get baseError => _subjectBaseError.stream;

  showError(CaughtException error) => _subjectBaseError.sink.add(error);

  User getCurrentUser() {
    final user = json.decode(_prefHelper.getUserData());
    return User.fromApiJson(user);
  }

  @mustCallSuper
  void dispose() {
    _subjectBaseError?.close();
  }
}

safe_api_call.dart

typedef AsyncCallback<T> = Future<Result<T>> Function();

Future<Result<T>> safeApiCall<T>(
    AsyncCallback<T> call, String errorMessage) async {
  try {
    return await call();
  } catch (e, stacktrace) {
    // An exception was thrown when calling the API
    // so we're returning a failure
    return Result.failure(e, stacktrace);
  }
}