如何在flutter中添加自动填充下拉菜单？

import 'package:flutter/material.dart';

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

class _MyFormState extends State<MyForm> {
  String _selectedItem;

  List<String> _items = [
    'Item 1',
    'Item 2',
    'Item 3',
    'Item 4',
    'Item 5',
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Auto-fill Dropdown'),
      ),
      body: Padding(
        padding: EdgeInsets.all(16.0),
        child: Column(
          children: [
            DropdownButtonFormField<String>(
              value: _selectedItem,
              items: _items.map((String value) {
                return DropdownMenuItem<String>(
                  value: value,
                  child: Text(value),
                );
              }).toList(),
              onChanged: (String newValue) {
                setState(() {
                  _selectedItem = newValue;
                });
              },
              decoration: InputDecoration(
                labelText: 'Select Item',
              ),
            ),
            SizedBox(height: 16.0),
            Text('Selected Item: $_selectedItem'),
          ],
        ),
      ),
    );
  }
}

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