CODEWITHSUNDEEP
flutterdartflutter-sharedpreference
sumseflut
sumseflut

Reputation: 678

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

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?

Upvotes: 49

Views: 75450

Answers (6)

Rahul Raj
Rahul Raj

Reputation: 1493

Here the solution for store and retrieve some list of object data to shared preference from api response

Here the sampleData carrying whole data from api and sampleList is the list to store shared preference

    SampleModel sampleData = await ApiCall();
    List<SampleDataItem> sampleList = sampleData.sampleList;

    //Convert sampleList to string
    String sampleStringList = jsonEncode(sampleList);
    
    print(sampleStringList);

    // Store to preference as string 
    PreferenceUtils.setSampleListData(sampleStringList);

Here the reverse that shared preference string data to object list model

    // get data from preference
String sampleDataFromPref = PreferenceUtils.getSampleListData();

// convert string data to jsonMap
var sampleJsonMap = json.decode(sampleDataFromPref);

// convert json map list to object model lis
List<SampleDataItem> sampleListFromPreferance = List<SampleDataItem>.from(jsonMap.map((x) => SampleDataItem.fromJson(x)));

// print the final output
print(sampleListFromPreferance);

Upvotes: 1

Tarun Jain
Tarun Jain

Reputation: 679

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']);

Upvotes: 5

Hamed Rezaee
Hamed Rezaee

Reputation: 7222

You should do these steps

to save the object:

  1. convert your object to map with toMap() method
  2. encode your map to string with encode(...) method
  3. save the string to shared preferences

for restoring your object:

  1. decode shared preference string to a map with decode(...) method
  2. 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();
}

Upvotes: 98

Michał Dobi Dobrzański
Michał Dobi Dobrzański

Reputation: 2000

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

Upvotes: 10

jayesh saha
jayesh saha

Reputation: 351

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()

Upvotes: 3

Rudresh Narwal
Rudresh Narwal

Reputation: 3100

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

Upvotes: 6

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