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<topic_end>
<topic_start>
What are the StatefulWidget and StatelessWidget best practices?
Here are a few things to consider when designing your widget.In Flutter, widgets are either Stateful or Stateless—depending on whether
they depend on a state change.In Flutter, there are three primary ways to manage state:When deciding which approach to use, consider the following principles:The MyStatefulWidget class manages its own state—it extends
StatefulWidget, it overrides the createState()
method to create the State object,
and the framework calls createState() to build the widget.
In this example, createState() creates an instance of
_MyStatefulWidgetState, which
is implemented in the next best practice.
<code_start>class MyStatefulWidget extends StatefulWidget {
const MyStatefulWidget({
super.key,
required this.title,
});
final String title;
@override
State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
@override
Widget build(BuildContext context) {
//...
}
}<code_end>
Add your custom StatefulWidget to the widget tree
in the app’s build method.
<code_start>class MyStatelessWidget extends StatelessWidget {
// This widget is the root of your application.
const MyStatelessWidget({super.key});
@override
Widget build(BuildContext context) {
return const MaterialApp(
title: 'Flutter Demo',
home: MyStatefulWidget(title: 'State Change Demo'),
);
}
}<code_end>
<topic_end>
<topic_start>
Props
In React Native, most components can be customized when they are
created with different parameters or properties, called props.
These parameters can be used in a child component using this.props.In Flutter, you assign a local variable or function marked
final with the property received in the parameterized constructor.
<code_start>/// Flutter
class CustomCard extends StatelessWidget {
const CustomCard({
super.key,
required this.index,
required this.onPress,
});
final int index;
final void Function() onPress;
@override
Widget build(BuildContext context) {
return Card(
child: Column(
children: <Widget>[
Text('Card $index'),
TextButton(
onPressed: onPress,
child: const Text('Press'),
),
],
),
);
}
}
class UseCard extends StatelessWidget {
const UseCard({super.key, required this.index});
final int index;
@override
Widget build(BuildContext context) {
/// Usage
return CustomCard(
index: index,
onPress: () {
print('Card $index');
},
);
}
}<code_end>
<topic_end>
<topic_start>
Local storage
If you don’t need to store a lot of data, and it doesn’t require
structure, you can use shared_preferences which allows you to
read and write persistent key-value pairs of primitive data
types: booleans, floats, ints, longs, and strings.<topic_end>
<topic_start>
How do I store persistent key-value pairs that are global to the app?
In React Native, you use the setItem and getItem functions
of the AsyncStorage component to store and retrieve data
that is persistent and global to the app.In Flutter, use the shared_preferences plugin to
store and retrieve key-value data that is persistent and global
to the app. The shared_preferences plugin wraps
NSUserDefaults on iOS and SharedPreferences on Android,
providing a persistent store for simple data.To add the shared_preferences package as a dependency, run flutter pub add: