仅当我重新加载整个应用程序时，才会显示DropdownButtonFormField的选定值

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

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

class _MyAppState extends State<MyApp> {
  String _selectedValue = '';

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

  Future<void> _loadSelectedValue() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      _selectedValue = prefs.getString('selectedValue') ?? '';
    });
  }

  Future<void> _saveSelectedValue(String value) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.setString('selectedValue', value);
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('DropdownButtonFormField Example'),
        ),
        body: Center(
          child: DropdownButtonFormField<String>(
            value: _selectedValue,
            onChanged: (newValue) {
              setState(() {
                _selectedValue = newValue;
                _saveSelectedValue(newValue);
              });
            },
            items: <String>['Option 1', 'Option 2', 'Option 3']
                .map<DropdownMenuItem<String>>((String value) {
              return DropdownMenuItem<String>(
                value: value,
                child: Text(value),
              );
            }).toList(),
          ),
        ),
      ),
    );
  }
}

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