define the provider

provider.dart

// in your startup main.dart file
RestClient(await buildDioClient())
RepositoryProvider(create: (context) => restClient, child: ....

// The class preceding the statefull class with the dropdown search
class AssetDialog extends StatelessWidget {
  final Asset asset;
  const AssetDialog(this.asset, {super.key});
  @override
  Widget build(BuildContext context) {
    return BlocProvider(
      create: (BuildContext context) =>
          ProductBloc(context.read<RestClient>(), context.read<String>())
            ..add(const ProductFetch(isForDropDown: true)),
      child: AssetDialogFull(asset),
    );
  }
}

// part of the statefull widget                   
BlocBuilder<ProductBloc, ProductState>(builder: (context, state) {
  switch (state.status) {
    case ProductStatus.failure:
      return const FatalErrorForm(
          message: 'server connection problem');
    case ProductStatus.success:
      return DropdownSearch<Product>(
        key: const Key('productDropDown'),
        selectedItem: _selectedProduct,
        popupProps: PopupProps.menu(
          showSearchBox: true,
          searchFieldProps: TextFieldProps(
            autofocus: true,
            decoration: InputDecoration(
                labelText: 'Product id'),
            controller: _productSearchBoxController,
          ),
          title: 'Product',
        ),
        dropdownDecoratorProps: DropDownDecoratorProps(
          dropdownSearchDecoration: InputDecoration(
            labelText: classificationId == 'AppHotel'
                ? 'Room Type'
                : 'Product',
          ),
        ),
        itemAsString: (Product? u) =>
            " ${u!.productName}", // invisible char for test
        onChanged: (Product? newValue) {
          _selectedProduct = newValue;
        },
        asyncItems: (String filter) {
          _productBloc.add(ProductFetch(searchString: filter));
          return Future.value(state.products);
        },
        validator: (value) =>
            value == null ? 'field required' : null,
      );
    default:
      return const Center(child: CircularProgressIndicator());
  }
}),