exmple-app-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: 'Startup Name Generator',
      home: RandomWords(),
    );
  }
}

class RandomWordsState extends State<RandomWords> {
  final List<WordPair> _suggestions = <WordPair>[];
  final List<WordPair> _saved = <WordPair>[]; // Add this line.
  final TextStyle _fontStyle = const TextStyle(fontSize: 18);

  Widget _buildWordsList(WordPair itemAt(int index)) {
    return ListView.builder(
      padding: const EdgeInsets.all(16),
      itemBuilder: (BuildContext context, int i) {
        final int index = i ~/ 2;
        final item = itemAt(index);
        if (item == null) {
          return null;
        }

        if (i.isOdd) {
          return Divider();
        }

        return _buildRow(item);
      },
    );
  }

  Widget _buildRow(WordPair pair) {
    final bool alreadySaved = _saved.contains(pair); // Add this line.

    return ListTile(
      title: Text(
        pair.asPascalCase,
        style: _fontStyle,
        textAlign: TextAlign.center,
      ),
      trailing: Icon(
        alreadySaved ? Icons.favorite : Icons.favorite_border,
        color: alreadySaved ? Colors.red : null,
      ),
      onTap: () {
        setState(() {
          if (alreadySaved) {
            _saved.remove(pair);
          } else {
            _saved.add(pair);
          }
        });
      },
    );
  }

  WordPair _suggestionsBuilder(int index) {
    if (index >= _suggestions.length) {
      _suggestions.addAll(generateWordPairs().take(10));
    }

    return _suggestions[index];
  }

  WordPair _favoriteWordGetter(int index) {
    if (index < _saved.length) {
      return _saved[index];
    }

    return null;
  }

  void _pushSaved() {
    Navigator.of(context).push(
      MaterialPageRoute<void>(
        builder: (BuildContext context) {
          return Scaffold(
              appBar: AppBar(
                title: Text("Favorites suggestions"),
              ),
              body: _buildWordsList(_favoriteWordGetter));
        },
      ),
    );
  }

  @override // Add from this line ...
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Startup Name Generator'),
        actions: <Widget>[
          IconButton(icon: Icon(Icons.list), onPressed: _pushSaved)
        ],
      ),
      body: _buildWordsList(_suggestionsBuilder),
    );
  }
}

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