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},
child: padding(
padding: const EdgeInsets.all(10),
child: Text('Row $i'),
),
),
);
}
return widgets;
}
}
<code_end>
<topic_end>
<topic_start>
how do i update ListView’s dynamically?
on android, you update the adapter and call notifyDataSetChanged.
in flutter, if you were to update the list of widgets inside a setState(),
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 {
const SampleApp({super.key});
// this widget is the root of your application.
@override
widget build(BuildContext context) {
return MaterialApp(
title: 'sample app',
theme: ThemeData(
colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
),
home: const SampleAppPage(),
);
}
}
class SampleAppPage extends StatefulWidget {
const SampleAppPage({super.key});
@override
State<SampleAppPage> createState() => _SampleAppPageState();
}
class _SampleAppPageState extends State<SampleAppPage> {
List<Widget> widgets = [];
@override
void initState() {
super.initState();
for (int i = 0; i < 100; i++) {
widgets.add(getRow(i));
}
}
@override
widget build(BuildContext context) {
return scaffold(
appBar: AppBar(
title: const Text('Sample app'),
),
body: ListView(children: widgets),
);
}
widget getRow(int i) {
return GestureDetector(
onTap: () {
setState(() {
widgets = list.from(widgets);
widgets.add(getRow(widgets.length));
developer.log('row $i');
});
},
child: padding(
padding: const EdgeInsets.all(10),
child: Text('Row $i'),
),
);
}
}
<code_end>
the recommended, efficient, and effective way to build a list uses a
ListView.Builder. this method is great when you have a dynamic
list or a list with very large amounts of data. this is essentially
the equivalent of RecyclerView on android, which automatically
recycles list elements for you:
<code_start>
import 'dart:developer' as developer;
import 'package:flutter/material.dart';
void main() {
runApp(const SampleApp());
}
class SampleApp extends StatelessWidget {
const SampleApp({super.key});
// this widget is the root of your application.