如何保存List< Object>到SharedPreferences扑朔迷离? [英] How to save List<Object> to SharedPreferences flutter?

问题描述

我有一个收藏的音乐列表，当我第一次打开该应用程序时，我会从音乐中检索该列表，该应用程序会从收藏夹"中获取一个收藏的音乐列表.我想将此列表保存到共享

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>();

音乐课在哪里:

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,
    );
  }
}

如何保存收藏的音乐列表?

How can I save favorite music list?

推荐答案

您应该执行以下步骤

保存对象:

1. 使用 toMap()方法
将您的对象转换为地图
2. 使用 encode(...)方法
将地图编码为字符串
3. 将字符串保存为共享首选项

用于还原对象:

1. 使用 decode(...)方法将共享的首选项字符串解码为地图
2. 使用 fromJson()方法获取对象

1. decode shared preference string to a map with decode(...) method
2. use fromJson() method to get your object

---

更新完整示例

import 'dart:convert';

void main() {
  final String encodedData = Music.encode([
    Music(id: 1, ...),
    Music(id: 2, ...),
    Music(id: 3, ...),
  ]);

  final List<Music> decodedData = Music.decode(encodedData);

  print(decodedData);
}

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();
}

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