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crossAxisCount: 2,
// Generate 100 widgets that display their index in the List.
children: List.generate(100, (index) {
return Center(
child: Text(
'Item $index',
style: Theme.of(context).textTheme.headlineSmall,
),
);
}),
),
),
);
}
}<code_end>
<topic_end>
<topic_start>Create lists with different types of items
You might need to create lists that display different types of content.
For example, you might be working on a list that shows a heading
followed by a few items related to the heading, followed by another heading,
and so on.Here’s how you can create such a structure with Flutter:<topic_end>
<topic_start>
1. Create a data source with different types of items
<topic_end>
<topic_start>
Types of items
To represent different types of items in a list, define
a class for each type of item.In this example, create an app that shows a header followed by five
messages. Therefore, create three classes: ListItem, HeadingItem,
and MessageItem.
<code_start>/// The base class for the different types of items the list can contain.
abstract class ListItem {
/// The title line to show in a list item.
Widget buildTitle(BuildContext context);
/// The subtitle line, if any, to show in a list item.
Widget buildSubtitle(BuildContext context);
}
/// A ListItem that contains data to display a heading.
class HeadingItem implements ListItem {
final String heading;
HeadingItem(this.heading);
@override
Widget buildTitle(BuildContext context) {
return Text(
heading,
style: Theme.of(context).textTheme.headlineSmall,
);
}
@override
Widget buildSubtitle(BuildContext context) => const SizedBox.shrink();
}
/// A ListItem that contains data to display a message.
class MessageItem implements ListItem {
final String sender;
final String body;
MessageItem(this.sender, this.body);
@override
Widget buildTitle(BuildContext context) => Text(sender);
@override
Widget buildSubtitle(BuildContext context) => Text(body);
}<code_end>
<topic_end>
<topic_start>
Create a list of items
Most of the time, you would fetch data from the internet or a local
database and convert that data into a list of items.For this example, generate a list of items to work with. The list
contains a header followed by five messages. Each message has one
of 3 types: ListItem, HeadingItem, or MessageItem.
<code_start>final items = List<ListItem>.generate(
1000,
(i) => i % 6 == 0
? HeadingItem('Heading $i')
: MessageItem('Sender $i', 'Message body $i'),
);<code_end>
<topic_end>
<topic_start>
2. Convert the data source into a list of widgets
To convert each item into a widget,
use the ListView.builder() constructor.In general, provide a builder function that checks for what type
of item you’re dealing with, and returns the appropriate widget
for that type of item.
<code_start>ListView.builder(
// Let the ListView know how many items it needs to build.
itemCount: items.length,
// Provide a builder function. This is where the magic happens.
// Convert each item into a widget based on the type of item it is.
itemBuilder: (context, index) {
final item = items[index];
return ListTile(
title: item.buildTitle(context),
subtitle: item.buildSubtitle(context),
);
},
)<code_end>
<topic_end>
<topic_start>
Interactive example
<code_start>import 'package:flutter/material.dart';
void main() {
runApp(