Hướng dẫn và ví dụ Flutter SharedPreferences

dependencies: 
  shared_preferences: ^2.2.3

import 'package:shared_preferences/shared_preferences.dart';

// Obtain shared preferences.
final prefs = await SharedPreferences.getInstance();

// Save an integer value to 'my_int_val' key.
await prefs.setInt('my_int_val', 10);

// Save an boolean value to 'my_bool_val' key.
await prefs.setBool('my_bool_val', true);

// Save an double value to 'my_double_val' key.
await prefs.setDouble('my_double_val', 1.5);

// Save an String value to 'my_note' key.
await prefs.setString('my_note', 'Go to the Beach');

// Save an list of strings to 'characters' key.
await prefs.setStringList('characters', ['Tom', 'Jerry', 'Donald']);

// Obtain shared preferences.
final prefs = await SharedPreferences.getInstance();

// Get an integer value from 'my_int_val' key.
int? intVal = await prefs.getInt('my_int_val');

// Get a boolean value from 'my_bool_val' key.
bool? boolVal = await prefs.getBool('my_bool_val');

// Get a double value from 'my_double_val' key.
double? doubleVal = await prefs.getDouble('my_double_val');

// Get a String value from 'my_note' key.
String? note = await prefs.getString('my_note');

// Get a list of strings from 'characters' key.
List<String>? characters = await prefs.getStringList('characters');

// Obtain shared preferences.
final prefs = await SharedPreferences.getInstance();

// Remove value for the 'my_int_val' key.
bool removed = await prefs.remove('my_int_val');

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 MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final TextEditingController controller = TextEditingController();
  String? myNote;

  @override
  void initState() {
    super.initState();
    //
    readMyNoteInSharedPreferences();
  }

  Future<void> readMyNoteInSharedPreferences() async {
    final prefs = await SharedPreferences.getInstance();
    myNote = await prefs.getString("my_note");
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: const Text('Flutter SharedPreferences Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text('My Note: $myNote'),
            const SizedBox(height: 10),
            TextField(
              controller: controller,
              decoration: const InputDecoration(
                border: OutlineInputBorder(),
                labelText: 'My Note',
                hintText: 'Enter a Note',
              ),
            ),
            const SizedBox(height: 10),
            ElevatedButton(
              onPressed: _saveMyNote,
              child: const Text("Save"),
            ),
          ],
        ),
      ),
    );
  }

  Future<void> _saveMyNote() async {
    final prefs = await SharedPreferences.getInstance();
    String text = controller.text;
    // Save a String to 'my_note' key of SharedPreferences.
    await prefs.setString("my_note", text);
    //
    ScaffoldMessenger.of(context).hideCurrentSnackBar();
    ScaffoldMessenger.of(context).showSnackBar(
      const SnackBar(content: Text("Saved!")),
    );
  }
}