I can't pull images from firebase_storage in my Flutter project

I decided to pull some of my image files from firebase storage in my Flutter application because the total size of the images is about 25gb. when I want to pull the images, I get some kind of ‘firebase cannot be called’ warning, how do I solve this problem?

If you can’t get an idea about the code, here’s a hint: I’m making an application that displays images with a page-turning animation. so the firebase operation must be compatible with this.

Warning Text

I/flutter ( 6311): Error getting image URL: [core/no-app] No Firebase App '[DEFAULT]' has been created - call Firebase.initializeApp()
I/chatty  ( 6311): uid=10148(com.example.libsy_app) 1.ui identical 2 lines
I/flutter ( 6311): Error getting image URL: [core/no-app] No Firebase App '[DEFAULT]' has been created - call Firebase.initializeApp()

This my code

import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/material.dart';
import 'package:page_flip/page_flip.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:firebase_storage/firebase_storage.dart' as firebase_storage;

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(AChristmasCarol());
}

final _controller = GlobalKey<PageFlipWidgetState>();

class AChristmasCarol extends StatefulWidget {
  const AChristmasCarol({Key? key}) : super(key: key);

  @override
  State<AChristmasCarol> createState() => _AChristmasCarolState();
}

class _AChristmasCarolState extends State<AChristmasCarol> {
  final _controller = GlobalKey<PageFlipWidgetState>();

  // sharedPreferences to store lastLeftOverPage Index
  final Future<SharedPreferences> _prefs = SharedPreferences.getInstance();

  // last left over page index
  int lastLeftOverPageIndex = 0;

  // SharedPreference key to retrieve the  value of lastLeftOverPageIndex
  String lastLeftOverPageNoPrefKey = "_lastLeftOverPageNoPrefKey";

  final List<String> imagesPath = [
    '/books/A Christmas Carol/page 1.png',
    '/books/A Christmas Carol/page 2.png',
    '/books/A Christmas Carol/page 3.png',
    '/books/A Christmas Carol/page 4.png',
  ];

  late List<String> downloadUrls;

  Widget _buildDemoPage(String imageUrl) {
    return FutureBuilder(
      future: _getImageUrl(imageUrl),
      builder: (BuildContext context, AsyncSnapshot<String?> snapshot) {
        if (snapshot.connectionState == ConnectionState.waiting) {
          return Center(child: CircularProgressIndicator());
        }
        if (snapshot.hasError || snapshot.data == null) {
          return Center(child: Text('Error fetching image'));
        }
        return Scaffold(
          body: Image.network(
            snapshot.data!,
            fit: BoxFit.cover,
          ),
        );
      },
    );
  }

  Future<String?> _getImageUrl(String imageUrl) async {
    try {
      final url = await firebase_storage.FirebaseStorage.instance
          .ref()
          .child(imageUrl)
          .getDownloadURL();
      return url;
    } catch (e) {
      print('Error getting image URL: $e');
      return null;
    }
  }

  @override
  void initState() {
    // restore the previous lastLeftOverPageIndex;
    _restoreLeftOverPage();
    super.initState();
  }

  Future<void> _restoreLeftOverPage() async {
    SharedPreferences pref = await _prefs;
    lastLeftOverPageIndex =
        pref.getInt(lastLeftOverPageNoPrefKey)?.toInt() ?? 0;
    // navigate the book page index to lastLeftOverPageIndex
    _controller.currentState?.goToPage(lastLeftOverPageIndex);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: PageFlipWidget(
        key: _controller,
        backgroundColor: Colors.white,
        initialIndex: lastLeftOverPageIndex,
        lastPage: Container(
            color: Colors.white, child: const Center(child: Text('The End!'))),
        children: [
          for (var imagePath in imagesPath) _buildDemoPage(imagePath),
        ],
      ),
      floatingActionButton: FloatingActionButton(
        child: const Icon(Icons.looks_one_outlined),
        onPressed: () {
          _controller.currentState?.goToPage(1);
        },
      ),
    );
  }

  @override
  void dispose() {
    super.dispose();
  }

  @override
  void deactivate() {
    super.deactivate();
    // before disposing the widget save the current page no
    var currentPageNo = _controller.currentState?.pageNumber.toInt() ?? 0;
    saveLastLeftOverPagePref(currentPageNo);
  }

  Future<void> saveLastLeftOverPagePref(int lastPage) async {
    SharedPreferences pref = await _prefs;
    pref.setInt(lastLeftOverPageNoPrefKey, lastPage);
  }
}