如何根据用户偏好在Flutter中选择日期格式

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  String _dateFormat = "yyyy-MM-dd"; // 默认日期格式

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

  // 从shared_preferences中加载日期格式
  void _loadDateFormat() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      _dateFormat = prefs.getString('dateFormat') ?? _dateFormat;
    });
  }

  // 保存日期格式到shared_preferences
  void _saveDateFormat(String format) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.setString('dateFormat', format);
    setState(() {
      _dateFormat = format;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('日期格式选择'),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                '当前日期格式：$_dateFormat',
                style: TextStyle(fontSize: 18),
              ),
              SizedBox(height: 20),
              RaisedButton(
                child: Text('选择日期格式'),
                onPressed: () {
                  _showFormatDialog();
                },
              ),
              SizedBox(height: 20),
              Text(
                '当前日期：${DateFormat(_dateFormat).format(DateTime.now())}',
                style: TextStyle(fontSize: 18),
              ),
            ],
          ),
        ),
      ),
    );
  }

  // 显示日期格式选择对话框
  void _showFormatDialog() {
    showDialog(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          title: Text('选择日期格式'),
          content: Column(
            mainAxisSize: MainAxisSize.min,
            children: <Widget>[
              ListTile(
                title: Text('yyyy-MM-dd'),
                onTap: () {
                  _saveDateFormat('yyyy-MM-dd');
                  Navigator.pop(context);
                },
              ),
              ListTile(
                title: Text('MM/dd/yyyy'),
                onTap: () {
                  _saveDateFormat('MM/dd/yyyy');
                  Navigator.pop(context);
                },
              ),
              // 其他日期格式选项...
            ],
          ),
        );
      },
    );
  }
}

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