dropdown_crasher.dart

import 'package:flutter/material.dart';

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

const List<String> items = <String>[
  'one',
  'two',
  'three',
];

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  MediaQueryData mediaQuery;
  String item = items[0];

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      builder: (BuildContext context, Widget child) {
        if (mediaQuery == null)
          mediaQuery = MediaQuery.of(context);
        return MediaQuery(
          data: mediaQuery,
          child: child,
        );
      },
      home: Scaffold(
        appBar: AppBar(title: Text('My App')),
        body: DropdownButton(
          value: item,
          items: items.map((String item) => DropdownMenuItem(
            value: item,
            child: Text(item),
          )).toList(),
          onChanged: (String newItem) {
            setState(() {
              item = newItem;
              mediaQuery = mediaQuery.copyWith(
                textScaleFactor: mediaQuery.textScaleFactor + 0.1,
              );
            });
          },
        ),
      ),
    );
  }
}