Multi-level dropdownbuttonformfield example

multi-level-dropdown.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: Center(
            child: Container(
                padding: EdgeInsets.symmetric(horizontal: 50, vertical: 30),
                child: Column(children: <Widget>[
                  DropdownButtonFormField<int>(
                    value: 2,
                    items: <DropdownMenuItem<int>>[
                      DropdownMenuItem<int>(
                        value: 1,
                        child: Text("One"),
                      ),
                      DropdownMenuItem<int>(
                        value: 2,
                        child: Text("Two"),
                      ),
                    ],
                    onChanged: (int value) {},
                  ),
                  DropdownButtonFormField<int>(
                    value: 2,
                    items: <DropdownMenuItem<int>>[
                      DropdownMenuItem<int>(
                        value: 1,
                        child: Text("Three"),
                      ),
                      DropdownMenuItem<int>(
                        value: 2,
                        child: Text("Four"),
                      ),
                    ],
                    onChanged: (int value) {},
                  ),
                  DropdownButtonFormField<int>(
                    value: 2,
                    items: <DropdownMenuItem<int>>[
                      DropdownMenuItem<int>(
                        value: 1,
                        child: Text("Five"),
                      ),
                      DropdownMenuItem<int>(
                        value: 2,
                        child: Text("Six"),
                      ),
                    ],
                    onChanged: (int value) {},
                  ),
                ]))));
  }
}

Implemented multi-level dropdowns using DropDownButtonFormField widget, that has 2 dropdown menu items each.

flutter/flutter#58989