SharedPreference不能在我的flutter应用程序上运行

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

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter SharedPreferences Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String _data = '';

  @override
  void initState() {
    super.initState();
    _loadData();
  }

  Future<void> _loadData() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      _data = prefs.getString('data') ?? '';
    });
  }

  Future<void> _saveData(String data) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.setString('data', data);
    setState(() {
      _data = data;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter SharedPreferences Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'Data from SharedPreferences:',
            ),
            Text(
              _data,
              style: TextStyle(fontSize: 20),
            ),
            SizedBox(height: 20),
            RaisedButton(
              onPressed: () {
                _saveData('Hello, SharedPreferences!');
              },
              child: Text('Save Data'),
            ),
          ],
        ),
      ),
    );
  }
}