DropDown Example

main.dart

import 'package:flutter/material.dart';

void main() => runApp(MaterialApp(home: MyApp()));

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) => Scaffold(
    body: Center(
      child:DropDownWidget(),),);
}

class DropDownWidget extends StatefulWidget {
  @override
  _DropDownWidgetState createState() => _DropDownWidgetState();
}

const _hintText = "hint";
Widget _hintWidget = Text(_hintText);
List<int> _values = [1, 2, 3, 4, 5];
List<DropdownMenuItem> _items = _values.map((v) => DropdownMenuItem(
  value: v,
  child: Text(v.toString()),
)).toList();

class _DropDownWidgetState extends State<DropDownWidget> {

  int _selectedValue = _values[0];
  void _setValue(int value) => setState(()=> _selectedValue = value);

  @override
  Widget build(BuildContext context) => DropdownButton<int>(
    hint: _hintWidget,
    value: _selectedValue,
    items: _items,
    onChanged: (value) => _setValue(value),
  );
}