如何在OnChanged中重置DropdownButtonField的值

import 'package:flutter/material.dart';

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  String dropdownValue = 'Option 1';
  List<String> dropdownOptions = ['Option 1', 'Option 2', 'Option 3'];

  void onChanged(String newValue) {
    setState(() {
      dropdownValue = newValue;
    });
  }

  void resetDropdownValue() {
    setState(() {
      dropdownValue = dropdownOptions[0];
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        DropdownButtonFormField<String>(
          value: dropdownValue,
          onChanged: onChanged,
          items: dropdownOptions.map((String value) {
            return DropdownMenuItem<String>(
              value: value,
              child: Text(value),
            );
          }).toList(),
        ),
        RaisedButton(
          onPressed: resetDropdownValue,
          child: Text('Reset'),
        ),
      ],
    );
  }
}