Work with long lists

The standard ListView constructor works well for small lists. To work with lists that contain a large number of items, it's best to use the ListView.builder constructor.

In contrast to the default ListView constructor, which requires creating all items at once, the ListView.builder() constructor creates items as they're scrolled onto the screen.

1. Create a data source

First, you need a data source. For example, your data source might be a list of messages, search results, or products in a store. Most of the time, this data comes from the internet or a database.

For this example, generate a list of 10,000 Strings using the List.generate constructor.

List<String>.generate(10000, (i) => 'Item $i'),

2. Convert the data source into widgets

To display the list of strings, render each String as a widget using ListView.builder(). In this example, display each String on its own line.

ListView.builder(
  itemCount: items.length,
  prototypeItem: ListTile(title: Text(items.first)),
  itemBuilder: (context, index) {
    return ListTile(title: Text(items[index]));
  },
)

Interactive example

import 'package:flutter/material.dart';

void main() {
  runApp(
    MyApp(
      items: List<String>.generate(10000, (i) => 'Item $i'),
    ),
  );
}

class MyApp extends StatelessWidget {
  final List<String> items;

  const MyApp({super.key, required this.items});

  @override
  Widget build(BuildContext context) {
    const title = 'Long List';

    return MaterialApp(
      title: title,
      home: Scaffold(
        appBar: AppBar(title: const Text(title)),
        body: ListView.builder(
          itemCount: items.length,
          prototypeItem: ListTile(title: Text(items.first)),
          itemBuilder: (context, index) {
            return ListTile(title: Text(items[index]));
          },
        ),
      ),
    );
  }
}

Children's extent

To specify each item's extent, you can use either prototypeItem, itemExtent, or itemExtentBuilder.

Specifying either is more efficient than letting the children determine their own extent because the scrolling machinery can make use of the foreknowledge of the children's extent to save work, for example when the scroll position changes drastically.

Use prototypeItem or itemExtent if your list has items of fixed size.

Use itemExtentBuilder if your list has items of different sizes.