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Flutter_Documentation

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class SampleAppPage extends StatefulWidget {
const SampleAppPage({super.key});
@override
State<SampleAppPage> createState() => _SampleAppPageState();
}
class _SampleAppPageState extends State<SampleAppPage> {
List<Widget> _getListData() {
return List<Widget>.generate(
100,
(index) => GestureDetector(
onTap: () {
developer.log('Row $index tapped');
},
child: Padding(
padding: const EdgeInsets.all(10),
child: Text('Row $index'),
),
),
);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: const Text('Sample App')),
body: ListView(children: _getListData()),
);
}
}<code_end>
<topic_end>
<topic_start>
How do I update a ListView dynamically?
In Xamarin.Forms, if you bound the
ItemsSource property to an ObservableCollection,
you would just update the list in your ViewModel.
Alternatively, you could assign a new List to the ItemSource property.In Flutter, things work a little differently.
If you update the list of widgets inside a setState() method,
you would quickly see that your data did not change visually.
This is because when setState() is called,
the Flutter rendering engine looks at the widget tree
to see if anything has changed.
When it gets to your ListView, it performs a == check,
and determines that the two ListViews are the same.
Nothing has changed, so no update is required.For a simple way to update your ListView,
create a new List inside of setState(),
and copy the data from the old list to the new list.
While this approach is simple, it is not recommended for large data sets,
as shown in the next example.
<code_start>import 'dart:developer' as developer;
import 'package:flutter/material.dart';
void main() {
runApp(const SampleApp());
}
class SampleApp extends StatelessWidget {
/// This widget is the root of your application.
const SampleApp({super.key});
@override
Widget build(BuildContext context) {
return const MaterialApp(
title: 'Sample App',
home: SampleAppPage(),
);
}
}
class SampleAppPage extends StatefulWidget {
const SampleAppPage({super.key});
@override
State<SampleAppPage> createState() => _SampleAppPageState();
}
class _SampleAppPageState extends State<SampleAppPage> {
List<Widget> widgets = <Widget>[];
@override
void initState() {
super.initState();
for (int i = 0; i < 100; i++) {
widgets.add(getRow(i));
}
}
Widget getRow(int index) {
return GestureDetector(
onTap: () {
setState(() {
widgets = List<Widget>.from(widgets);
widgets.add(getRow(widgets.length));
developer.log('Row $index');
});
},
child: Padding(
padding: const EdgeInsets.all(10),
child: Text('Row $index'),
),
);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: const Text('Sample App')),
body: ListView(children: widgets),
);
}
}<code_end>