import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';
  final _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    var items = [
      'Ayo',
      'This',
      'Don',
      'Look',
      'Right',
    ].map((String val) {
      return DropdownMenuItem(
        value: val,
        child: Text(
          val,
        ),
      );
    }).toList();

    return MaterialApp(
      title: _title,
      theme: ThemeData(
        inputDecorationTheme: const InputDecorationTheme(
          border: OutlineInputBorder(
            borderRadius: BorderRadius.all(Radius.circular(32)),
            borderSide: BorderSide(color: Colors.blue, width: 2),
          ),
        ),
      ),
      home: Scaffold(
        body: Center(
          child: SizedBox(
            width: 500,
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                Form(
                  key: _formKey,
                  child: DropdownButtonFormField(
                    onTap: () {
                      _formKey.currentState!.validate();
                    },
                    validator: (String? v) => 'Required',
                    onChanged: (String? value) {},
                    items: items,
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}