My flutter learning

main.dart

import 'package:flutter/material.dart';
import 'package:english_words/english_words.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Welcome to Flutter',
      home: new HomePage());
  }

}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(appBar: new AppBar(
      title: new Text('Page 2'),
      actions: <Widget>[ // Add 3 lines from here...
        new IconButton(icon: const Icon(Icons.apps),
            onPressed: () => navigateSecondPage(context)),
      ],
    ),
      body: Center(
        child: new RandomWords(),
      ),
    );
  }

  void navigateSecondPage(BuildContext context) {
    Navigator.of(context).pushReplacement(
        new MaterialPageRoute<void>(
        builder: (BuildContext context){
          return new Scaffold( // Add 6 lines from here...
              appBar: new AppBar(
              title: const Text('Second Page'),
          ),
        body: new Center(child: new Text("Hello Second Page")),);
        },
      ),
    );
  }
}


class RandomWords extends StatefulWidget {
  @override
  RandomWordsState createState() => new RandomWordsState();
}

class RandomWordsState extends State<RandomWords> {
  final _suggestions = <WordPair>[];
  final Set<WordPair> _saved = new Set<WordPair>(); // Add this line.
  final _biggerFont = const TextStyle(fontSize: 32.0);

  @override
  Widget build(BuildContext context) {
    return _buildListView();
  }

  Widget _buildListView() {
    return ListView.builder(
        padding: const EdgeInsets.all(16.0),

        itemBuilder: (context, i) {
          if (i.isOdd) return Divider();
          final index = i ~/ 2;
          if (index >= _suggestions.length) {
            _suggestions.addAll(generateWordPairs().take(10));
          }
          return _buildRow(_suggestions[index]);
        }
    );
  }

  Widget _buildRow(WordPair pair) {
    final bool alreadySaved = _saved.contains(pair); // Add this line.
    return ListTile(
      title: Text(
        pair.asPascalCase,
        style: _biggerFont,
      ),
      trailing: new Icon( // Add the lines from here...
        alreadySaved ? Icons.favorite : Icons.favorite_border,
        color: alreadySaved ? Colors.red : null,
      ), onTap: () {
      // Add 9 lines from here...
      setState(() {
        if (alreadySaved) {
          _saved.remove(pair);
        } else {
          _saved.add(pair);
        }
      });
    },
    );
  }
}