如何在flutter中保存变量并使其可供我的所有文件访问？

dependencies:
  flutter:
    sdk: flutter
  provider: ^6.0.1

import 'package:flutter/material.dart';

class AppState extends ChangeNotifier {
  String myVariable = '';

  void updateVariable(String newValue) {
    myVariable = newValue;
    notifyListeners();
  }
}

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

void main() {
  runApp(
    ChangeNotifierProvider(
      create: (context) => AppState(),
      child: MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'My App',
      home: MyHomePage(),
    );
  }
}

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

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    var appState = Provider.of<AppState>(context);

    return Scaffold(
      appBar: AppBar(
        title: Text('My Home Page'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(appState.myVariable),
            ElevatedButton(
              onPressed: () {
                appState.updateVariable('New Value');
              },
              child: Text('Update Variable'),
            ),
          ],
        ),
      ),
    );
  }
}

dependencies:
  flutter:
    sdk: flutter
  shared_preferences: ^2.0.10

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

class MyPage extends StatelessWidget {
  final myVariableKey = 'myVariable';

  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: () async {
        SharedPreferences prefs = await SharedPreferences.getInstance();
        prefs.setString(myVariableKey, 'New Value');
      },
      child: Text('Save Variable'),
    );
  }
}

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

class AnotherPage extends StatelessWidget {
  final myVariableKey = 'myVariable';

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<String>(
      future: _getVariable(),
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          return Text(snapshot.data!);
        } else {
          return CircularProgressIndicator();
        }
      },
    );
  }

  Future<String> _getVariable() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    return prefs.getString(myVariableKey) ?? '';
  }
}