flutter-examples/infinite_list/lib/example.dart

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

// Example: an infinitely scrolling list that generates new word pairs on demand.
class Example extends StatefulWidget {
  const Example({super.key});

  @override
  State<Example> createState() => _ExampleState();
}

class _ExampleState extends State<Example> {
  final _suggestions = <WordPair>[];
  final _saved = <WordPair>{};
  final _biggerFont = const TextStyle(fontSize: 18.0);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Infinite List'),
        centerTitle: true,
        actions: <Widget>[
          IconButton(icon: const Icon(Icons.list), onPressed: _pushSaved),
        ],
      ),
      body: _buildSuggestions(),
    );
  }

  void _pushSaved() {
    Navigator.of(context).push(
      MaterialPageRoute(
        builder: (context) {
          final tiles = _saved.map(
            (pair) {
              return ListTile(
                title: Text(
                  pair.asPascalCase,
                  style: _biggerFont,
                ),
              );
            },
          );
          final divided = ListTile.divideTiles(
            context: context,
            tiles: tiles,
          ).toList();

          return Scaffold(
            appBar: AppBar(
              title: const Text('Saved lists'),
            ),
            body: ListView(children: divided),
          );
        },
      ),
    );
  }

  Widget _buildRow(WordPair pair) {
    final alreadySaved = _saved.contains(pair);
    return ListTile(
      title: Text(
        pair.asPascalCase,
        style: _biggerFont,
      ),
      trailing: Icon(
        alreadySaved ? Icons.favorite : Icons.favorite_border,
        color: alreadySaved ? Colors.red : null,
      ),
      onTap: () {
        setState(() {
          if (alreadySaved) {
            _saved.remove(pair);
          } else {
            _saved.add(pair);
          }
        });
      },
    );
  }

  Widget _buildSuggestions() {
    return ListView.builder(
        padding: const EdgeInsets.all(16.0),
        // The itemBuilder callback is called once per suggested word pairing,
        // and places each suggestion into a ListTile row.
        // For even rows, the function adds a ListTile row for the word pairing.
        // For odd rows, the function adds a Divider widget to visually
        // separate the entries. Note that the divider may be difficult
        // to see on smaller devices.
        itemBuilder: (context, i) {
          // Add a one-pixel-high divider widget before each row in theListView.
          if (i.isOdd) return const Divider();

          // The syntax "i ~/ 2" divides i by 2 and returns an integer result.
          // For example: 1, 2, 3, 4, 5 becomes 0, 1, 1, 2, 2.
          // This calculates the actual number of word pairings in the ListView,
          // minus the divider widgets.
          final index = i ~/ 2;
          // If you've reached the end of the available word pairings...
          if (index >= _suggestions.length) {
            // ...then generate 10 more and add them to the suggestions list.
            _suggestions.addAll(generateWordPairs().take(10));
          }
          return _buildRow(_suggestions[index]);
        });
  }
}