Retrieving items in cart

Question

I'm trying to retrieve the items in the usercart from firebase. It's in this format :1231352385:2. The getitemsquantity() is retrieving the count.

I need to use in the firebase query using whereIn, but its async - so i can't use await in the query.

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:get_it/get_it.dart';
import 'package:ionicons/ionicons.dart';
import 'package:order_sage_user/Services/firebaseservices.dart';
import 'package:order_sage_user/models/sellers.dart';
import 'package:order_sage_user/models/sellersitems.dart';
import 'package:provider/provider.dart';

import '../Services/sharedpreferences.dart';
import '../models/cart_item_counter.dart';
import '../widgets/cart_items_designs.dart';

class CartScreen extends StatefulWidget {
  final String? selleruid;
  CartScreen({this.selleruid, Key? key}) : super(key: key);

  @override
  State<CartScreen> createState() => _CartScreenState();
}

class _CartScreenState extends State<CartScreen> {
  late User _user;
  late double _deviceHeight, _deviceWidth;
  late MySharedPreferences _sharedPreferences;
  late FireBaseService _fireBaseService;

  List<int> separateItemQuantityList = [];

  getItemsQuantities() async {
    List<String> defaultItemList = [];
    int i = 0;

    defaultItemList = await _fireBaseService.getUserCart();

    for (i; i < defaultItemList.length; i++) {
      // this is a list so we used this function to get each item in the list
      String item = defaultItemList[i].toString();

      List<String> listItemCharacters = item.split(':').toList();
      //this is to get the number which is the first index after the : split and assign it to the quantity number
      var quantityNumber = int.parse(listItemCharacters[1].toString());

      print('\nthis is quantity Number now = ' + quantityNumber.toString());

      separateItemQuantityList.add(quantityNumber);
    }
    print('\nthis is Quantity list now = ');
    print(separateItemQuantityList);
  }

  @override
  void initState() {
    super.initState();
    _sharedPreferences = MySharedPreferences();
    _fireBaseService = GetIt.instance.get<FireBaseService>();
    _user = FirebaseAuth.instance.currentUser!;

    getItemsQuantities();
  }

  @override
  Widget build(BuildContext context) {
    _deviceHeight = MediaQuery.of(context).size.height;
    _deviceWidth = MediaQuery.of(context).size.width;

    return MultiProvider(
      providers: [
        ChangeNotifierProvider(
          create: (context) => CartItemCounter(_sharedPreferences),
        )
      ],
      child: Scaffold(
        appBar: AppBar(
          backgroundColor: Colors.transparent,
          elevation: 0,
          leading: IconButton(
            onPressed: () {
              Navigator.pop(context);
            },
            icon: Icon(
              Ionicons.chevron_back,
              color: Color(0xFF76966D),
            ),
          ),
          actions: [
            Stack(
              children: [
                IconButton(
                  onPressed: () {},
                  icon: Icon(
                    Ionicons.cart,
                    size: 30,
                    color: Color(0xFF76966D),
                  ),
                ),
                Positioned(
                  top: 8,
                  right: 8,
                  child: Container(
                    padding: EdgeInsets.all(4),
                    decoration: BoxDecoration(
                        color: Color(0xFF76966D), shape: BoxShape.circle),
                    child: Consumer<CartItemCounter>(
                      builder: (context, counter, child) {
                        return Text(
                          counter.count.toString(),
                          style: TextStyle(color: Colors.white),
                        );
                      },
                    ),
                  ),
                )
              ],
            ),
          ],
        ),
        floatingActionButton: Row(
          mainAxisAlignment: MainAxisAlignment.spaceAround,
          children: [
            Align(
              alignment: Alignment.bottomLeft,
              child: FloatingActionButton.extended(
                onPressed: () {},
                label: Text('Clear Cart'),
                icon: Icon(Icons.clear_all),
                backgroundColor: Colors.blue,
              ),
            ),
            Align(
              alignment: Alignment.bottomLeft,
              child: FloatingActionButton.extended(
                onPressed: () {},
                label: Text('Checkout'),
                icon: Icon(Icons.navigate_next),
                backgroundColor: Colors.blue,
              ),
            ),
          ],
        ),
        body: CustomScrollView(
          slivers: [
            StreamBuilder<QuerySnapshot>(
              stream: FirebaseFirestore.instance
                  .collection('items')
                  .where('itemId', whereIn: getItemsQuantities())
                  .orderBy('itemtime', descending: true)
                  .snapshots(),
              builder: (context, snapshot) {
                return !snapshot.hasData
                    ? SliverToBoxAdapter(
                        child: Center(
                          child: CircularProgressIndicator(),
                        ),
                      )
                    : snapshot.data!.docs.isEmpty
                        ? Container()
                        : SliverList(delegate:
                            SliverChildBuilderDelegate((context, index) {
                            Itemsmodel model = Itemsmodel.fromJson(
                                snapshot.data!.docs[index].data()!
                                    as Map<String, dynamic>);
                            return CartItemDesign(
                              model: model,
                              context: context,
                              itemsQuantityList: [index],
                            );
                          }));
              },
            )
          ],
        ),
      ),
    );
  }
}

ive tried to use a futurebuilder above the streambuilder but that also did not work