Persistent storage
- Flutter course
- Intermediate
- Lesson 84/99
- 4 min
Persist notes with shared_preferences.
Storing with shared_preferences
To make notes permanent you use the shared_preferences package. You first serialize the note list to a JSON string with jsonEncode, then store it with prefs.setString('notlar', s). When the app opens you read this string with prefs.getString('notlar'), decode it with jsonDecode, and convert it to a list with Note.fromJson.
final prefs = await SharedPreferences.getInstance();
final s = jsonEncode(notlar.map((n) => n.toJson()).toList());
await prefs.setString('notlar', s);Reading and decoding
When reading the stored string you check the result of prefs.getString('notlar'). If the string exists you decode it into a List with jsonDecode and convert each element to a model with Note.fromJson. If it does not exist you start with an empty list.
final s = prefs.getString('notlar');
if (s == null) return [];
final liste = jsonDecode(s) as List;
return liste.map((e) => Note.fromJson(e as Map<String, dynamic>)).toList();Practice The notlariKaydet function
Write an async function named notlariKaydet. Get prefs with SharedPreferences.getInstance(), serialize the note list with jsonEncode (using notlar.map((n) => n.toJson()).toList()), then save it with prefs.setString('notlar', s). Print 'hazir' in main.
Starter code
import 'dart:convert';
import 'package:shared_preferences/shared_preferences.dart';
class Note {
final String id;
final String baslik;
final String icerik;
Note(this.id, this.baslik, this.icerik);
Map<String, dynamic> toJson() => {'id': id, 'baslik': baslik, 'icerik': icerik};
}
// notlariKaydet fonksiyonunu yaz
// prefs örneğini al
// notlar listesini dizeleştir
// 'notlar' anahtarıyla kalıcı olarak kaydet
void main() {
// 'hazir' yazdır
}Sample solution
import 'dart:convert';
import 'package:shared_preferences/shared_preferences.dart';
class Note {
final String id;
final String baslik;
final String icerik;
Note(this.id, this.baslik, this.icerik);
Map<String, dynamic> toJson() => {'id': id, 'baslik': baslik, 'icerik': icerik};
}
Future<void> notlariKaydet(List<Note> notlar) async {
final prefs = await SharedPreferences.getInstance();
final s = jsonEncode(notlar.map((n) => n.toJson()).toList());
await prefs.setString('notlar', s);
}
void main() {
print('hazir');
}Expected output
hazir
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is done before saving the note list to shared_preferences?
- Serialize the list to a JSON string with jsonEncode Correct answer
- Wrap the list in a Future
- Convert the list to a Widget
- Write the list to an sqflite table
Explanation: shared_preferences only stores primitive types; so you first serialize the note list with jsonEncode. Wrapping in a Future, converting to a Widget, and writing to sqflite are different operations and not needed here.
2 Store as a String
final s = jsonEncode(notlar.map((n) => n.toJson()).toList());
await prefs.____('notlar', s);final s = jsonEncode(notlar.map((n) => n.toJson()).toList());
await prefs.setString('notlar', s);Explanation: To store a string in shared_preferences you use setString. getString is for reading, setInt is for numbers, and there is no method called setList.
3 Persistent storage parts
| Term | Meaning |
|---|---|
shared_preferences |
Persistent storage |
jsonEncode |
Serializing the list |
setString |
Writing a string |
jsonDecode |
Decoding the string |