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<topic_start>
supported types
although the key-value storage provided by shared_preferences is
easy and convenient to use, it has limitations:
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<topic_start>
testing support
it’s a good idea to test code that persists data using shared_preferences.
to enable this, the package provides an
in-memory mock implementation of the preference store.
to set up your tests to use the mock implementation,
call the setMockInitialValues static method in
a setUpAll() method in your test files.
pass in a map of key-value pairs to use as the initial values.
<code_start>
SharedPreferences.setMockInitialValues(<String, object>{
'counter': 2,
});
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<topic_start>
complete example
<code_start>
import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
void main() => runApp(const MyApp());
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
widget build(BuildContext context) {
return const MaterialApp(
title: 'shared preferences demo',
home: MyHomePage(title: 'shared preferences demo'),
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage({super.key, required this.title});
final string title;
@override
State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
@override
void initState() {
super.initState();
_loadCounter();
}
/// load the initial counter value from persistent storage on start,
/// or fallback to 0 if it doesn't exist.
future<void> _loadCounter() async {
final prefs = await SharedPreferences.getInstance();
setState(() {
_counter = prefs.getInt('counter') ?? 0;
});
}
/// after a click, increment the counter state and
/// asynchronously save it to persistent storage.
future<void> _incrementCounter() async {
final prefs = await SharedPreferences.getInstance();
setState(() {
_counter = (prefs.getint('counter') ?? 0) + 1;
prefs.setInt('counter', _counter);
});
}
@override
widget build(BuildContext context) {
return scaffold(
appBar: AppBar(
title: text(widget.title),
),
body: center(
child: column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
const text(
'you have pushed the button this many times: ',
),
text(
'$_counter',
style: Theme.of(context).textTheme.headlineMedium,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'increment',
child: const Icon(Icons.add),
),
);
}
}
<code_end>
<topic_end>
<topic_start>
read and write files