import 'package:flutter/material.dart';

class MyStatefulWidget extends StatefulWidget {

  MyStatefulWidget({Key key}) : super(key: key);

  @override

  _MyStatefulWidgetState createState() => _MyStatefulWidgetState();

}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {

  String dropdownValue = 'One';

  @override

  Widget build(BuildContext context) {

    return Scaffold(

      body: Center(

        child: DropdownButton<String>(

          value: dropdownValue,

          onChanged: (String newValue) {

            setState(() {

              dropdownValue = newValue;

            });

          },

          items: <String>['One', 'Two', 'Free', 'Four']

              .map<DropdownMenuItem<String>>((String value) {

            return DropdownMenuItem<String>(

              value: value,

              child: Text(value),

            );

          }).toList(),

        ),

      ),

    );

  }

}