如何在颤动DropdownButtonFormField中重置值

import 'package:flutter/material.dart';

class MyForm extends StatefulWidget {
  @override
  _MyFormState createState() => _MyFormState();
}

class _MyFormState extends State<MyForm> {
  String _selectedValue = ''; // 用于存储当前选中的值

  List<String> _dropdownValues = ['选项1', '选项2', '选项3']; // 下拉菜单的选项列表

  void _resetForm() {
    setState(() {
      _selectedValue = ''; // 将选中的值重置为空字符串
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        DropdownButtonFormField<String>(
          value: _selectedValue, // 设置当前选中的值
          items: _dropdownValues.map((value) {
            return DropdownMenuItem<String>(
              value: value,
              child: Text(value),
            );
          }).toList(),
          onChanged: (newValue) {
            setState(() {
              _selectedValue = newValue; // 当下拉菜单的值改变时更新选中的值
            });
          },
        ),
        RaisedButton(
          child: Text('重置'),
          onPressed: _resetForm, // 点击按钮时调用重置方法
        ),
      ],
    );
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('重置下拉菜单')),
        body: Center(
          child: MyForm(),
        ),
      ),
    );
  }
}

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