flutter使用Shared Preferences进行数据持久化的示例代码

以下是使用Shared Preferences进行数据持久化的示例代码：

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

class ExamplePage extends StatefulWidget {
  @override
  _ExamplePageState createState() => _ExamplePageState();
}

class _ExamplePageState extends State<ExamplePage> {
  TextEditingController _controller = TextEditingController();
  String _savedText = '';

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

  void _loadSavedText() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    String savedText = prefs.getString('savedText') ?? '';
    setState(() {
      _savedText = savedText;
      _controller.text = savedText;
    });
  }

  void _saveText(String text) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.setString('savedText', text);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Example Page'),
      ),
      body: Padding(
        padding: EdgeInsets.all(16.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            TextField(
              controller: _controller,
              decoration: InputDecoration(
                labelText: 'Enter some text',
              ),
              onChanged: (text) {
                _saveText(text);
              },
            ),
            SizedBox(height: 16.0),
            Text(
              'Saved text: $_savedText',
              style: TextStyle(fontSize: 18.0),
            ),
          ],
        ),
      ),
    );
  }
}

在上述代码中，我们首先在initState()方法中加载之前保存的文本，并将其设置为文本框的默认值。然后，我们在文本框中输入文本时使用SharedPreferences实例保存文本。最后，我们将保存的文本显示在屏幕上。