how can I send data from one class to a stateful widget in Flutter

I want to be able to make progress bar where the value changes based on a function. My problem is I am working with 3 different files. The first file main_page_test.dart where the code for calling the function is held. enigma_test.dart where the code for the function is held. Finally, loading_alert_dialog.dart where I keep the code for the AlertDialog containing the ProgressBar

To clarify, I want the application to display the AlertDialog when the function is called in main_page_test.dart. While the function is running I want it to update the ProgressBar and pass the filename of the file it is working on encrypting.

If there is anything else I can clarify on please let me know.

Here is the relevant code for main_page_test.dart:

import 'dart:io';

import 'package:fluent_ui/fluent_ui.dart';
import 'package:file_picker/file_picker.dart';

import '../functions/enigma_test.dart';

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

  @override
  State<MainPageTest> createState() => _MainPageTestState();
}

class _MainPageTestState extends State<MainPageTest> {
  final double _buttonTextSize = 20.0;
  final double _widgetWidth = 200.0;

  List<File>? _files;

  late final TextEditingController _textController;
  late final FlyoutController _flyoutController;

  @override
  void initState() {
    super.initState();
    _textController = TextEditingController();
    _flyoutController = FlyoutController();
  }

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

  void pickFiles() async {
    FilePickerResult? result = await FilePicker.platform.pickFiles(
      type: FileType.custom,
      allowedExtensions: ['txt'],
      allowMultiple: true,
    );

    if (result != null) {
      setState(() {
        _files = result.paths.map((path) => File(path!)).toList();
      });
    } else {
      setState(() {
        _files = null;
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        children: [
          Padding(
            padding: const EdgeInsets.all(8.0),
            child: SizedBox(
              width: _widgetWidth,
              child: Button(
                onPressed: () {
                  pickFiles();
                },
                child: Padding(
                  padding: const EdgeInsets.symmetric(vertical: 12.0),
                  child: Text(
                    'Choose Files',
                    style: TextStyle(
                      fontSize: _buttonTextSize,
                    ),
                  ),
                ),
              ),
            ),
          ),
          Padding(
            padding: const EdgeInsets.symmetric(horizontal: 12.0),
            child: SizedBox(
              width: _widgetWidth,
              child: Button(
                onPressed: () async {
                  await EnigmaTest().encrypt(_files!);
                },
                child: Padding(
                  padding: const EdgeInsets.symmetric(vertical: 12.0),
                  child: Text(
                    'Encrypt',
                    style: TextStyle(
                      fontSize: _buttonTextSize,
                    ),
                  ),
                ),
              ),
            ),
          ),
        ],
      ),
    );
  }
}

Here is the relevant code for enigma_test.dart:

import 'dart:developer';
import 'dart:io';
import 'package:path_provider/path_provider.dart';
import 'package:path/path.dart' as p;

import 'package:encrypt/encrypt.dart';

class EnigmaTest {
  Future<void> encrypt(List<File> files) async {
    const String keyAsString = '123';
    final String encryptedPath = p.join(await _localPath, 'encrypted');
    final Key key = Key.fromUtf8(keyAsString.padRight(32, ' '));

    try {
      for (File file in files) {
        final contents = await file.readAsLines();
        // getting the name of the file without the extension
        final filename = p.basename(file.path);

        File encrypedFile =
            await File(p.join(encryptedPath, filename)).create(recursive: true);

        var sink = encrypedFile.openWrite();

        for (String line in contents) {
          if (line == '') {
            sink.writeln();
          } else {
            var encryptedLine = _aesEncryption(line, key);
            sink.writeln(encryptedLine);
          }
        }

        await sink.flush();
        await sink.close();
      }
    } catch (e) {
      //somethibng
      inspect(e);
    }
  }

  String _aesEncryption(String line, Key key) {
    final iv = IV.fromLength(16);
    final encrypter = Encrypter(AES(key));
    final encrypted = encrypter.encrypt(line, iv: iv);
    return encrypted.base16;
  }

  Future<String> get _localPath async {
    final documentsDirectory = await getApplicationDocumentsDirectory();
    final encyptedFilesDirectory =
        p.join(documentsDirectory.path, "Dead Man's Enigma Output");

    return encyptedFilesDirectory;
  }
}

Here is the code for loading_alert_dialog.dart:

import 'package:fluent_ui/fluent_ui.dart';

class MyLoadingAlertDialog {
  static showLoadingAlert(
      BuildContext context, String filename, double progress) {
    showDialog(
      context: context,
      builder: (context) {
        return ContentDialog(
          title: const Text('Progress'),
          content: Column(
            children: [
              SizedBox(
                width: double.infinity,
                child: ProgressBar(value: progress, strokeWidth: 8),
              ),
              Padding(
                padding: const EdgeInsets.all(4.0),
                child: Text(
                  'currently encrypting $filename...',
                  style: const TextStyle(
                      fontSize: 10.0, fontStyle: FontStyle.italic),
                ),
              ),
            ],
          ),
        );
      },
    );
  }
}