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flutter_docs

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// 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(