flutter_bloc.md

Changes in flutter_bloc package

New version number:

• flutter_bloc: 8.1.2

---

Requirements:

Upgrading to v8.1.2 in flutter-multipliers will require us to upgrade the flutter_bloc and bloc in following packages:

Non-breaking bloc migrations:

• deriv_auth, deriv_web_view, deriv_bloc_manager.

Breaking bloc migrations:

• flutter_deriv_api, update_checker.
• mapEventToState has been removed since bloc 8.0.0. We will need to change mapEventToState to onEvent in these packages.

-We also have to upgrade bloc_test to v9.1.1, wherever we have upgraded flutter_bloc.

Resolving issues:

• Since flutter_bloc v8.0.0, BlocUnhandledErrorException has been removed, which results in following error as we have used it in our test cases.

• Add // ignore: invalid_use_of_protected_member to cubit.addError.

  The name 'BlocUnhandledErrorException' isn't a type, so it can't be used as a type argument.
  Try correcting the name to an existing type, or defining a type named 'BlocUnhandledErrorException'.
  

  We have used this exception in test/features/chart/state/chart_setting/chart_setting_cubit_test.dart.

      test(
          'should emit a [$ChartSettingFailureState] when the service throws '
          'an exception',
          () async {
          when(service.getSetting).thenThrow(Exception('Test exception'));
  
          expect(
              chartSettingCubit.loadLastSetting,
              throwsA(isA<BlocUnhandledErrorException>()),
          );
          expect(
              chartSettingCubit.state,
              isA<ChartSettingFailureState>(),
          );
          },
      );
  

  We came to the conclusion to remove the assertion for BlocUnhandledErrorException and not add any replacements as well due to the reason below:

  /// Loads last saved chart setting from shared preferences.
  Future<void> loadLastSetting() async {
      try {
      final ChartSettingModel setting = await _service.getSetting();
      emit(ChartSettingLoadedState(setting));
      } on Exception catch (error, stackTrace) {
      emit(ChartSettingFailureState(message: '$error', setting: state.setting));
      addError(error, stackTrace);
      }
  }
  

  The above snippet is from the method we are testing. We can see that we are catching the exception and calling bloc.addError method which reports error to bloc.onError. As per changelog of bloc v8.0.0, only uncaught exceptions are rethrown by bloc.onError. Since, it is a caught exception, it will not be rethrown and only log the error to the console as we have added log in our BlocObserver. So, there will not be any exceptions thrown to test. We can change the test case to the following:

  test(
          'should emit a [$ChartSettingFailureState] when the service throws '
          'an exception',
          () async {
          when(service.getSetting).thenThrow(Exception('Test exception'));
          await chartSettingCubit.loadLastSetting();
          expect(
              chartSettingCubit.state,
              isA<ChartSettingFailureState>(),
          );
          },
      );

  • Warning: The member 'addError' can only be used within instance members of subclasses of 'package:bloc/src/bloc_base.dart'. This is received in the following code snippet.

  blocTest<TickStreamCubit, TickStreamState>(
          'captures exceptions.',
          build: () => TickStreamCubit(),
          act: (TickStreamCubit cubit) => cubit.addError(exception),
          errors: () => <Matcher>[equals(exception)],
      );

  The above lint error/warning is due to bloc.addError being protected in the new version. Upon checking the official git repository of bloc to see how the addError is being tested, we found that they have added //ignore: invalid_use_of_protected_member in the file to remove the lint error. We can do the same in our test cases as we haven't found the alternative way to test the case without having to use the protected addError.