Unsupported operation: Cannot add to an unmodifiable list unsing Bloc

March 17, 2023

i am using bloc to add and remove from am list..

my bloc state is like this,

@freezed
class InterestActionState with _$InterestActionState {
  factory InterestActionState({
    required bool isSubmitting,
    required List<String> selectedInterest,
    required Option<Either<InterestFailure, Unit>>
        intrestFailureOrSuccessOption,
  }) = Initial;

  factory InterestActionState.initial() => InterestActionState(
        isSubmitting: false,
        selectedInterest: <String>[],
        intrestFailureOrSuccessOption: none(),
      );

  const InterestActionState._();
}

also i am adding to the list like this

  void addInterestToMyList(
    AddMyList event,
    Emitter<InterestActionState> emit,
  ) {
    emit(state.copyWith(
        selectedInterest: state.selectedInterest..add(event.selectedInterest)));

}

and to Remove from the List is

 void removeInterestToMyList(
    RemoveFromList event,
    Emitter<InterestActionState> emit,
  ) {
    emit(state.copyWith(
        selectedInterest: state.selectedInterest
          ..remove(event.selectedInterest)));
  }

but i keep getting flutter: Unsupported operation: Cannot add to an unmodifiable list

>Solution :

state.selectedInterest must be unmodifiable, and remove and add modify the list in place (it modifies the list and doesn’t create a copy).

You can create a copy yourself using .toList():

Add:

 void addInterestToMyList(
    AddMyList event,
    Emitter<InterestActionState> emit,
  ) {
    emit(state.copyWith(
        selectedInterest: state.selectedInterest.toList()..add(event.selectedInterest)));

Remove:

void removeInterestToMyList(
    RemoveFromList event,
    Emitter<InterestActionState> emit,
  ) {
    emit(state.copyWith(
        selectedInterest: state.selectedInterest.toList()
          ..remove(event.selectedInterest)));
  }