如何在Flutter中使用DropdownButton中的TextEditingController？

import 'package:flutter/material.dart';

class MyDropdownButton extends StatefulWidget {
  @override
  _MyDropdownButtonState createState() => _MyDropdownButtonState();
}

class _MyDropdownButtonState extends State<MyDropdownButton> {
  TextEditingController _controller = TextEditingController();
  String _selectedValue;

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('DropdownButton with TextEditingController'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            DropdownButton<String>(
              value: _selectedValue,
              onChanged: (String newValue) {
                setState(() {
                  _selectedValue = newValue;
                  _controller.text = newValue; // 更新TextEditingController的文本
                });
              },
              items: <String>['Option 1', 'Option 2', 'Option 3', 'Option 4']
                  .map<DropdownMenuItem<String>>((String value) {
                return DropdownMenuItem<String>(
                  value: value,
                  child: Text(value),
                );
              }).toList(),
            ),
            SizedBox(height: 20),
            Text(
              'Selected Value: ${_controller.text}',
              style: TextStyle(fontSize: 18),
            ),
          ],
        ),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: MyDropdownButton(),
  ));
}