How to change state of individual list items using bloc flutter?

Question

How to change the widgets in a list item in flutter using bloc pacakage. Should i use BlockBuilder or listener on the whole ListView.builder or only the individual items. It would be nice if u share an example or tutorial. eg If i have a checkbox i need to change its state on clicking it. These are my Bloc classes Bloc

const String SERVER_FAILURE_MESSAGE = 'Server Failure';
const String CACHE_FAILURE_MESSAGE = 'Cache Failure';
class MarkAttendanceBloc extends Bloc<MarkAttendanceEvent, MarkAttendanceState> {

  final MarkStudentPresent markStudentPresent;
  final MarkStudentAbsent markStudentAbsent;

  MarkAttendanceBloc({@required this.markStudentPresent,@required this.markStudentAbsent});

  @override
  MarkAttendanceState get initialState => MarkedInitial();

  @override
  Stream<MarkAttendanceState> mapEventToState(MarkAttendanceEvent event) async* {
    yield MarkedLoading();
    if(event is MarkAbsentEvent){
      final remotelyReceived = await markStudentAbsent(MarkStudentParams(classId: event.classId, courseId: event.courseId,studentId: event.studentId));
      yield* _eitherLoadedOrErrorState(remotelyReceived);
    }
    else if(event is MarkPresentEvent){
      final remotelyReceived = await markStudentPresent(MarkStudentParams(classId: event.classId, courseId: event.courseId,studentId: event.studentId));
      yield* _eitherLoadedOrErrorState(remotelyReceived);
    }
  }
  Stream<MarkAttendanceState> _eitherLoadedOrErrorState(
    Either<StudentDetailsFacultyFailure,int> failureOrClasses,
    ) async* {
    yield failureOrClasses.fold(
        (failure) => MarkedError(_mapFailureToMessage(failure)),
        (studentId) => Marked(studentId),
    );
  }
  String _mapFailureToMessage(StudentDetailsFacultyFailure failure) {
    switch (failure.runtimeType) {
      case ServerError:
        return SERVER_FAILURE_MESSAGE;
      default:
        return 'No internet';
    }
  }

}

State

abstract class MarkAttendanceState extends Equatable{
  const MarkAttendanceState();
}

class MarkedInitial extends MarkAttendanceState{
  const MarkedInitial();
  @override
  List<Object> get props => [];

}

class MarkedLoading extends MarkAttendanceState{
  const MarkedLoading();
  @override
  List<Object> get props => [];

}

class Marked extends MarkAttendanceState{
  final int studentId;

  Marked(this.studentId);

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

}

class MarkedError extends MarkAttendanceState{
  final String errorMessage;
  MarkedError(this.errorMessage);
  @override
  List<Object> get props => [errorMessage];
}

Event

import 'package:equatable/equatable.dart';

abstract class MarkAttendanceEvent extends Equatable {
  const MarkAttendanceEvent();
}
class MarkPresentEvent extends MarkAttendanceEvent {
  final int studentId;
  final int courseId;
  final int classId;

  MarkPresentEvent(this.studentId, this.courseId, this.classId);

  @override
  List<Object> get props =>[studentId,courseId,classId];

}

class MarkAbsentEvent extends MarkAttendanceEvent {
  final int studentId;
  final int courseId;
  final int classId;

  MarkAbsentEvent(this.studentId, this.courseId, this.classId);

  @override
  List<Object> get props =>[studentId,courseId,classId];

}

Answer 1

Maybe by now you have found a solution but this is how i managed to achieve the same functionality using flutter cubits. This code is hand written and not tested but it should guide you to achieve your goal

1 Declare the class objects

    class ClassItem{
      int? price;
      bool isChecked;
    
      ClassItem({
        this.price,
        this.isChecked=false,
      });
}
    class ClassOverall{
      List<ClassItem> items;
      double? total;
      ClassOverall(this.items,this.total);
    }

2. Declare the cubit class

     class OverallCubit extends Cubit<ClassOverall> {
     OverallCubit(ClassOverallinitialState) : super(initialState);
   
     void checkUncheckCart(int index) {
     if (!state.items
         .elementAt(index).isChecked) {
       state.items
               .elementAt(index).isChecked =
           !state.items
               .elementAt(index).isChecked;
       var t_total = double.tryParse(state.items
               .elementAt(index).price!)! * 1;
       emit(OverallCubit (state.items,state.total));
     } else {
       state.items.elementAt(index).isChecked =
           !state.items
               .elementAt(index).isChecked;
       emit(OverallCubit (state.items,state.total));
     }
     calculateTotal();
   }
   void calculateTotal() {
     var tot = 0.0;
       for (var tick in state.items) {
         if (tick.isChecked) {
           tot = (tick.t_total! + tot);
   
     }
   
     }
   emit(OverallCubit (state.items,tot));
    }
    }
   

3. Declare the top class widget to hold the state

   class TopState extends StatelessWidget {
         @override
         Widget build(BuildContext context) {
           return BlocProvider(
             create: (_) => OverallCubit(ClassOverall(items,0)),//fetch items from your source 
             child: Home(),
           );
         }
       }
   

4. Declare the stateful widget and add a bloc builder

    class Home extends StatefulWidget {
           @override
      _HomePageState createState() => _HomePageState();
    }
   
    class _HomePageState extends State<Home> {
      @override
      Widget build(BuildContext context) {
        return  BlocBuilder<OverallCubit, ClassOverall>(
                                  builder: (ctx, state) {
    return Column(children:[ 
    ListView.builder(
    padding: EdgeInsets.all(0.0),
                                          shrinkWrap: true,
                                          itemCount: state.items.length,
                                          itemBuilder: (context, index) {
                                            return ListTile(
    onTap: () {
                ctx
                    .read<OverallCubit>()
                    .checkUncheckCart(index);
              },
    tileColor: state.elementAt(index).isChecked ? Colors.red : Colors.white
    title: Text(state.items.elementAt(index).price!),
    );
    }),
    Text(state.total.toString),
    ]);
                                     });
    }
   
    }