Flutter -如何使用BloC实现下拉列表？

dependencies:
  flutter_bloc: ^7.0.0

import 'package:flutter_bloc/flutter_bloc.dart';

enum DropdownEvent {
  fetchOptions,
}

class DropdownState {
  final List<String> options;

  DropdownState(this.options);
}

class DropdownBloc extends Bloc<DropdownEvent, DropdownState> {
  DropdownBloc() : super(DropdownState([]));

  @override
  Stream<DropdownState> mapEventToState(DropdownEvent event) async* {
    if (event == DropdownEvent.fetchOptions) {
      // 模拟异步获取下拉列表选项的过程
      await Future.delayed(Duration(seconds: 2));
      yield DropdownState(['Option 1', 'Option 2', 'Option 3']);
    }
  }
}

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

class DropdownWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocProvider(
      create: (context) => DropdownBloc()..add(DropdownEvent.fetchOptions),
      child: Scaffold(
        appBar: AppBar(
          title: Text('Dropdown Example'),
        ),
        body: BlocBuilder<DropdownBloc, DropdownState>(
          builder: (context, state) {
            if (state.options.isEmpty) {
              return Center(child: CircularProgressIndicator());
            } else {
              return DropdownButton<String>(
                value: null,
                items: state.options.map((option) {
                  return DropdownMenuItem<String>(
                    value: option,
                    child: Text(option),
                  );
                }).toList(),
                onChanged: (value) {
                  // 处理下拉列表选项变化的逻辑
                },
              );
            }
          },
        ),
      ),
    );
  }
}