如何在flutter中创建下拉选项卡

import 'package:flutter/material.dart';

String selectedOption;

DropdownButton<String>(
  value: selectedOption,
  items: <String>['选项1', '选项2', '选项3', '选项4'].map((String value) {
    return DropdownMenuItem<String>(
      value: value,
      child: Text(value),
    );
  }).toList(),
  onChanged: (String newValue) {
    setState(() {
      selectedOption = newValue;
    });
  },
),

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: '下拉选项卡示例',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String selectedOption;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('下拉选项卡示例'),
      ),
      body: Center(
        child: DropdownButton<String>(
          value: selectedOption,
          items: <String>['选项1', '选项2', '选项3', '选项4'].map((String value) {
            return DropdownMenuItem<String>(
              value: value,
              child: Text(value),
            );
          }).toList(),
          onChanged: (String newValue) {
            setState(() {
              selectedOption = newValue;
            });
          },
        ),
      ),
    );
  }
}