How to compare state or get data from state or use state of flutter bloc cubit?

Question

I'm new to flutter BloC and I'm confused about its state usage. From the counter app, I built another basic app to show a different widget based on its state. But not sure how to do that.

Cubits:

part 'home_bloc_state.dart';

class HomeBlocCubit extends Cubit<HomeBlocState> {
  HomeBlocCubit() : super(HomeBlocInitial());


  void showHome() {
    emit(HomeBlocInitial());
  }

  void showStudents() {
    emit(HomeBlocStudents());
  }


}

//state

part of 'home_bloc_cubit.dart';


@immutable
abstract class HomeBlocState {}

class HomeBlocInitial extends HomeBlocState {}
class HomeBlocStudents extends HomeBlocState {} 

With a button widget I can add/toggle events:

final myBloc = BlocProvider.of<HomeBlocCubit>(context);

 return Container(
  child: ElevatedButton(
        onPressed: () { 
          myBloc.showHome(); 
        }, 
        child: Text('Home'),
      ), )

To show events on UI I would like to return a Text widget based on state.

@override
  Widget build(BuildContext context) {
    return Container(child: Align(child:
        BlocBuilder<HomeBlocCubit, HomeBlocState>(
            builder: (context, state) {
              //do something based on state.
              //How to check or compare or get data from this state?
              switch (state) {
                case   HomeBlocState: //error, - how to use?
                  break;
              }
      return Text(
        "Welcome to this page: " + state.toString(),
        style: TextStyle(
            fontSize: 60 ),
      );
    })));
  }

How to show UI based on state?

Answer 1

With Dart 3 you may leverage pattern matching and sealed classes. Now it is possible to change state like that:

sealed class HomeBlocState {}
class HomeBlocInitial extends HomeBlocState {}
class HomeBlocStudents extends HomeBlocState {} 

and use pattern matching in the builder:

return switch(state) {
  HomeBlocInitial() => LoadingView(),
  HomeBlocStudents() => StudentsList(),
};

---

old answer

You may check whether state is in a required state by calling

if (state is HomeBlocInitial) {
  ...
}

If you prefer switches:

switch (state.runtimeType) {
  case HomeBlocInitial:
    return const HomeInitial();
  default:
    // probably throw
    return const SizedBox();
}

A more mature approach (if you're good with code generation) would be to use freezed for states. In that case, your state would be declared as:

@freezed
class HomeBlocState with _$Failfast{
  const factory HomeBlocState.initial() = _Initial;
  const factory HomeBlocState.students() = _Students;
}

And inside BlocBuilder you'll have:

return state.map(
  initial: (initialState) => ...,
  students: (studentsState) => ...,
);