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.
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.
dart
List
<
String
>.
generate
(
10000
, (i) =>
'Item
$
i
'
),
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.
dart
ListView
.
builder
(
itemCount: items.length,
prototypeItem:
ListTile
(
title:
Text
(items.first),
),
itemBuilder: (context, index) {
return
ListTile
(
title:
Text
(items[index]),
);
},
)
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]),
);
},
),
),
);
}
}
To specify each item's extent, you can use either
itemExtent
or
prototypeItem
. 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.