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Flutter_Documentation

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),
);
}
}
class ItemWidget extends StatelessWidget {
const ItemWidget({
super.key,
required this.text,
});
final String text;
@override
Widget build(BuildContext context) {
return Card(
child: SizedBox(
height: 100,
child: Center(child: Text(text)),
),
);
}
}<code_end>
<topic_end>
<topic_start>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.<topic_end>
<topic_start>
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.
<code_start>List<String>.generate(10000, (i) => 'Item $i'),<code_end>
<topic_end>
<topic_start>
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.
<code_start>ListView.builder(
itemCount: items.length,
prototypeItem: ListTile(
title: Text(items.first),
),
itemBuilder: (context, index) {
return ListTile(
title: Text(items[index]),
);
},
)<code_end>
<topic_end>
<topic_start>
Interactive example
<code_start>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]),
);
},
),
),
);
}
}<code_end>
<topic_end>
<topic_start>
Children’s extent
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.
<topic_end>
<topic_start>Scrolling
Flutter has many built-in widgets that automatically