How to save List<Object> to SharedPreferences in Flutter? - flutter

Question

I have a list of favorite music, which I retrieve from music when the app is opened for the first time, the app gets a favorite music list from favorite. I want to save this list to shared
preferences.List<Music> favoriteMusic = new List<Music>();
where music class is:
class Music {
final int id;
final String name, size, rating, duration, img;
bool favorite;
Music({
this.id,
this.rating,
this.size,
this.duration,
this.name,
this.img,
this.favorite,
});
factory Music.fromJson(Map<String, dynamic> jsonData){
return Music(
id: jsonData['id'],
rating: jsonData['rating'],
size: jsonData['size'],
duration: jsonData['duration'],
name: jsonData['name'],
img: jsonData['img'],
favorite: false,
);
}
}
How can I save favorite music list?

Answer 1

You should do these steps
to save the object:
convert your object to map with toMap() method
encode your map to string with encode(...) method
save the string to shared preferences
for restoring your object:
decode shared preference string to a map with decode(...) method
use fromJson() method to get your object
UPDATE FULL SAMPLE
import 'dart:convert';
void main() async {
final SharedPreferences prefs = await SharedPreferences.getInstance();
// Encode and store data in SharedPreferences
final String encodedData = Music.encode([
Music(id: 1, ...),
Music(id: 2, ...),
Music(id: 3, ...),
]);
await prefs.setString('musics_key', encodedData);
// Fetch and decode data
final String musicsString = await prefs.getString('musics_key');
final List<Music> musics = Music.decode(musicsString);
}
class Music {
final int id;
final String name, size, rating, duration, img;
bool favorite;
Music({
this.id,
this.rating,
this.size,
this.duration,
this.name,
this.img,
this.favorite,
});
factory Music.fromJson(Map<String, dynamic> jsonData) {
return Music(
id: jsonData['id'],
rating: jsonData['rating'],
size: jsonData['size'],
duration: jsonData['duration'],
name: jsonData['name'],
img: jsonData['img'],
favorite: false,
);
}
static Map<String, dynamic> toMap(Music music) => {
'id': music.id,
'rating': music.rating,
'size': music.size,
'duration': music.duration,
'name': music.name,
'img': music.img,
'favorite': music.favorite,
};
static String encode(List<Music> musics) => json.encode(
musics
.map<Map<String, dynamic>>((music) => Music.toMap(music))
.toList(),
);
static List<Music> decode(String musics) =>
(json.decode(musics) as List<dynamic>)
.map<Music>((item) => Music.fromJson(item))
.toList();
}

Answer 2

Flutter's shared_preferences plugin has a method: setStringList(String key, List<String> value), so you can just write serializer for your objects.

Answer 3

Convert it to a string, you can store it
import 'dart:convert';
...
var s = json.encode(myList);
// or var s = jsonEncode(myList);
json.decode() //convert a string to List when you load it

Answer 4

For noob folks like me who want to understand a bit more about the magic our dear friend Hamed did in his answer, or want to adapt his solution to more complex classes with lists/other classes, check out these two links:
https://bezkoder.com/dart-flutter-parse-json-string-array-to-object-list/
https://bezkoder.com/dart-flutter-convert-object-to-json-string/
jsonEncode() and jsonDecode() are the same as json.encode() and json.decode()

Answer 5

simply use stringlist in shared preferences
basic syntax:
// read
final myStringList = prefs.getStringList('my_string_list_key') ?? [];
// write
prefs.setStringList('my_string_list_key', ['a', 'b', 'c']);
Firstly convert the object to a map. Then convert the map to a JSON string using jsonEncode and at the end save the JSON string to shared preferences
Sample example:
// import 'dart:convert';
Person person = Person('Mary', 30);
Map<String, dynamic> map = {
'name': person.name,
'age': person.age
};
String rawJson = jsonEncode(map);
prefs.setString('my_string_key', rawJson);
retrieve data
final rawJson = prefs.getString('my_string_key') ?? '';
Map<String, dynamic> map = jsonDecode(rawJson);
final person = Person(map['name'], map['age']);