Write Your First App example using both the Marterial design or the Cupertino design.

write_your_first_app.dart

import 'dart:io' show Platform;

import 'package:flutter/foundation.dart' show kIsWeb;

import 'package:english_words/english_words.dart';

import 'package:flutter/material.dart';

import 'package:flutter/cupertino.dart';

void main() => runApp(MyApp(
      switchUI: true,
    ));

class MyApp extends StatelessWidget {
  MyApp({
    this.key,
    this.android = false,
    this.iOS = false,
    this.switchUI = false,
  }) {
    _useMaterial = android;
    _useCupertino = iOS;
    _switchUI = switchUI;
  }
  final Key key;
  final bool android;
  final bool iOS;
  final bool switchUI;

  static bool _useMaterial;
  static bool _useCupertino;
  static bool _switchUI;

  @override
  Widget build(BuildContext context) {
    String title = 'Startup Name Generator';
    Widget home = RandomWords(key: key);
    if (useCupertino) {
      return CupertinoApp(
        title: title,
        home: home,
      );
    } else {
      return MaterialApp(
        title: title,
        home: home,
      );
    }
  }

  // Use Material UI when explicitly specified or even when running in iOS
  static bool get useMaterial =>
      (_useMaterial && !_useCupertino) ||
      (Platform.isAndroid && !_switchUI && !_useCupertino) ||
      (Platform.isIOS && _switchUI) ||
      (kIsWeb && !_switchUI);

  // Use Cupertino UI when explicitly specified or even when running in Android
  static bool get useCupertino =>
      (_useCupertino && !_useMaterial) ||
      (Platform.isIOS && !_switchUI && !_useMaterial) ||
      (Platform.isAndroid && _switchUI) ||
      (kIsWeb && _switchUI);
}

class RandomWords extends StatefulWidget {
  RandomWords({
    Key key,
    this.useMaterial = false,
    this.useCupertino = false,
    this.switchUI = false,
  }) : super(key: key);
  final bool useMaterial;
  final bool useCupertino;
  final bool switchUI;
  @override
  State createState() =>
      MyApp.useMaterial ? RandomWordsAndroid() : RandomWordsApple();
}

class RandomWordsAndroid extends State<RandomWords> {
  RandomWordsAndroid() {
    wordPair = _WordPair(this);
  }
  _WordPair wordPair;
  final _biggerFont = const TextStyle(fontSize: 18.0);
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Startup Name Generator'),
      ),
      body: ListView.builder(
          padding: const EdgeInsets.all(16.0),
          itemBuilder: (context, i) {
            if (i.isOdd) return Divider();
            wordPair.build(i);
            return ListTile(
              title: Text(
                wordPair.current.asPascalCase,
                style: _biggerFont,
              ),
              trailing: wordPair.icon,
              onTap: () {
                wordPair.onTap(i);
              },
            );
          }),
    );
  }
}

class RandomWordsApple extends State<RandomWords> {
  RandomWordsApple() {
    wordPair = _WordPair(this);
  }
  _WordPair wordPair;
  @override
  Widget build(BuildContext context) {
    return CupertinoPageScaffold(
      child: CustomScrollView(
        slivers: <Widget>[
          const CupertinoSliverNavigationBar(
            largeTitle: Text('Startup Name Generator'),
          ),
          SliverSafeArea(
            top: false,
            minimum: const EdgeInsets.only(top: 8),
            sliver: SliverList(
              delegate: SliverChildBuilderDelegate(
                (context, i) {
                  if (i.isOdd) return Divider();
                  wordPair.build(i);
                  return CupertinoListTile(
                    title: wordPair.current.asPascalCase,
                    trailing: wordPair.icon,
                    onTap: () {
                      wordPair.onTap(i);
                    },
                  );
                },
              ),
            ),
          )
        ],
      ),
    );
  }
}

class _WordPair {
  _WordPair(this.state);
  final State state;
  final suggestions = <WordPair>[];
  final Set<WordPair> saved = <WordPair>{};
  int index;

  void build(int i) {
    index = i ~/ 2;
    if (index >= suggestions.length) {
      suggestions.addAll(generateWordPairs().take(10));
    }
  }

  WordPair get current => suggestions[index];

  Icon get icon {
    bool alreadySaved = saved.contains(suggestions[index]);
    return Icon(
      alreadySaved ? Icons.favorite : Icons.favorite_border,
      color: alreadySaved ? Colors.red : null,
    );
  }

  void onTap(int i) => state.setState(() {
        int index = i ~/ 2;
        WordPair pair = suggestions[index];
        if (pair == null) return;
        if (saved.contains(suggestions[index])) {
          saved.remove(pair);
        } else {
          saved.add(pair);
        }
      });
}

/// Cupertino needs a ListTile equivalent
/// https://github.com/flutter/flutter/issues/50668#issuecomment-593060684
class CupertinoListTile extends StatefulWidget {
  const CupertinoListTile({
    Key key,
    this.leading,
    this.title,
    this.subtitle,
    this.trailing,
    this.onTap,
  }) : super(key: key);
  final Widget leading;
  final String title;
  final String subtitle;
  final Widget trailing;
  final Function onTap;
  @override
  _StatefulStateCupertino createState() => _StatefulStateCupertino();
}

class _StatefulStateCupertino extends State<CupertinoListTile> {
  @override
  Widget build(BuildContext context) {
    Widget leading;
    if (widget.leading == null) {
      leading = const SizedBox();
    } else {
      leading = widget.leading;
    }
    Widget trailing;
    if (widget.trailing == null) {
      trailing = const SizedBox();
    } else {
      trailing = widget.trailing;
    }
    return GestureDetector(
      onTap: () {
        if (widget.onTap != null) widget.onTap();
      },
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceBetween,
        children: <Widget>[
          Row(
            children: <Widget>[
              leading,
              SizedBox(width: 10),
              Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: columnChildren(context),
              ),
            ],
          ),
          trailing,
        ],
      ),
    );
  }

  List<Widget> columnChildren(BuildContext context) {
    List<Widget> children = List();
    bool isDark = MediaQuery.of(context).platformBrightness == Brightness.dark;
    Widget title = widget.title != null
        ? Text(
            widget.title,
            style: TextStyle(
                fontSize: 25.0, color: isDark ? Colors.white : Colors.black),
          )
        : const SizedBox();
    children.add(title);
    if (widget.subtitle != null)
      children.add(Text(widget.subtitle,
          style: TextStyle(color: CupertinoColors.systemGrey)));
    return children;
  }
}