Flutter Bloc 如何从 Widget 本身更新 BlocBuilder 中的 Widget？

Question

How can to update a Bloc widget from the bloc Widget itself with the Slider?

The Event for the Chart Data is executed from another Widget. When the data is fetched this Widget is opened. When I change the Slider I want the chart to be updated withe the date but keep the other data. Would be too much to fetch all the Data again.

How can I get access only the data changed from the same widget?

I have the following Bloc Builder Widget, bloc_event, bloc and bloc_state

The Widget:

class ChartWidget extends StatelessWidget {
ChartWidget({Key key}) : super(key: key);

@override
Widget build(BuildContext context) {

double valueSliderDate;
return BlocBuilder<ChartDataBloc, ChartDataState>(
  builder: (context, state) {
    if (state is ChartDataLoadInProgress) {
      return LoadingIndicator();
    } else if (state is ChartDataLoadSuccess) {
      final chartData = state.chartData;
      final maxValueAll = getMaxValueAll(chartData);
      final List<double> dates = getValuesDate(chartData);
      valueSliderDate = dates.first;

      return Column(children: <Widget>[
        
        Expanded(
          child: MyFancyChart(chartData, valueSliderDate),
        ),
        Slider(
          min: dates.first,
          max: dates.last,
           divisions: dates.length,
           value: valueSliderDate,
          onChanged: (value) {
            context.read<ChartDataBloc>().add(DateSliderSet(value));
          },
        ),
      ]);
    } else {
      return Container();
    }
  },
);
}

This is the bloc_event with two events:

abstract class ChartDataEvent {
const ChartDataEvent();
@override
List<Object> get props => [];  }

class SpecificIndicatorIdSet extends ChartDataEvent {
const SpecificIndicatorIdSet(this.indicator);
final Indicator indicator;

@override
List<Object> get props => [indicator];  }

class DateSliderSet extends ChartDataEvent {
const DateSliderSet(this.dateSlider);
final double dateSlider;

@override
List<Object> get props => [dateSlider];  }

This is the bloc itself:

class ChartDataBloc extends Bloc<ChartDataEvent, ChartDataState> {
final ChartDataRepository chartDataRepository;
ChartDataBloc({@required this.chartDataRepository}) : super(ChartDataLoadInProgress());

@override
Stream<ChartDataState> mapEventToState(ChartDataEvent event) async* {
if (event is SpecificIndicatorIdSet) {
yield* _mapIndicatorsLoadedToState(event);
} else if (event is DateSliderSet) {
yield* _mapDateSliderToState(event);  }    }

Stream<ChartDataState> _mapDateSliderToState(
  DateSliderSet event
  ) async* {
try {
  final dateSlider = event.dateSlider;
  yield DateSliderLoadSuccess(
    dateSlider,
  );
} catch (_) {
  yield DateSliderLoadFailure();  }   }

Stream<ChartDataState> _mapIndicatorsLoadedToState(
  SpecificIndicatorIdSet event
  ) async* {
try {
  final chartData = await this.chartDataRepository.loadChartData(event.indicator.id);
  yield ChartDataLoadSuccess(
    sortToListOfLists(chartData),
    event.indicator.name
  );
} catch (_) {
  yield ChartDataLoadFailure();  }  }  }

This is the bloc_state:

abstract class ChartDataState {
const ChartDataState();
@override
List<Object> get props => [];  }

class ChartDataLoadInProgress extends ChartDataState {}

class ChartDataLoadSuccess extends ChartDataState {
final List<List<ChartData>> chartData;
final String titleIndicator;
const ChartDataLoadSuccess(this.chartData,this.titleIndicator);

@override
List<Object> get props => [chartData, titleIndicator];

@override
String toString() => 'ChartDataLoadSuccess { topics: ' + chartData + ' }';  }

class ChartDataLoadFailure extends ChartDataState {}

class DateSliderLoadSuccess extends ChartDataState {
final double dateSlider;
const DateSliderLoadSuccess(this.dateSlider);

@override
List<Object> get props => [dateSlider];

@override
String toString() => 'DateSliderLoadSuccess { dateSlider: ' + dateSlider.toString() + ' }';  
}

class DateSliderLoadFailure extends ChartDataState {}

Thanks in advance

Answer 1

Have you tried creating a variable inside your bloc to store the original data?

You would be able to store the data and be able to continue using your bloc and updating your widget.