在共享首选项中保存嵌套对象

Question

我有一个包含 json 数组的对象，它正试图存储在共享首选项中，但我不知道该怎么做。

这是我的模型：

import 'dart:convert';

import 'package:deepnrise/models/settings/perimeter.dart';
import 'package:deepnrise/models/user/user_perims.dart';

UserWithPerim user(String str) => UserWithPerim.fromJson(json.decode(str));

class UserWithPerim {
  // ignore: non_constant_identifier_names
  UserWithPerim({
    required this.identifier,
    required this.firstName,
    required this.lastName,
    required this.email,
    required this.role,
    required this.perimeters,
  });

  String identifier;
  String firstName;
  String lastName;
  String email;
  String role;
  List<UserPerimeter> perimeters;

  factory UserWithPerim.fromJson(Map<String, dynamic> json) {
    return UserWithPerim(
      identifier: json['identifier'] ?? "",
      firstName: json['firstName'] ?? "",
      lastName: json['lastName'] ?? "",
      email: json['email'] ?? "",
      role: json['role'] ?? "",
      perimeters: (json['perimeters'] as List)
          .map((p) => UserPerimeter.fromJson(p))
          .toList(),
    );
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['identifier'] = identifier;
    data['firstName'] = firstName;
    data['lastName'] = lastName;
    data['role'] = role;
    data['email'] = email;
    data['perimeters'] = perimeters;
    return data;
  }
}

这是周长模型：

import 'dart:convert';

Userperimeters(String str) => UserPerimeter.fromJson(json.decode(str));

String UserPerimToJson(UserPerimeter data) => json.encode(data.tojson());

class UserPerimeter {
  // ignore: non_constant_identifier_names
  UserPerimeter(
      {required this.id, required this.label, required this.perimeterId});
  // ignore: non_constant_identifier_names
  int id;
  String label;
  int perimeterId;

  factory UserPerimeter.fromJson(Map<String, dynamic> json) {
    return UserPerimeter(
        id: json['id'] ?? "",
        label: json['label'] ?? "",
        perimeterId: json["perimeterId"] ?? "");
  }

  Map<String, dynamic> tojson() => {
        "id": id,
        "label": label,
        "perimeterId": perimeterId,
      };
}

现在我有两种用户对象模型，一种包含风险列表，另一种不包含，因为每当我尝试将用户存储在共享首选项中时，都会抛出此异常：

Unhandled Exception: type 'UserPerimeter' is not a subtype of type 'Map<String, dynamic>'

这是我保存和读取用户的方式：

  saveUser(value) async {
    final prefs = await SharedPreferences.getInstance();
    String user = jsonEncode(User.fromJson(value));
    prefs.setString(Preferences.USER_KEY, user);
  }

Future<User?> getUser() async {
    final prefs = await SharedPreferences.getInstance();
    if (prefs.containsKey(Preferences.USER_KEY)) {
      Map<String, dynamic> userMap =
          jsonDecode(prefs.getString(Preferences.USER_KEY) ?? "");
      User user = User.fromJson(userMap);
      return user;
    }
  }

有没有一种方法可以在不创建用户对象的两个模型的情况下将整个用户模型与风险对象列表一起存储？非常感谢你。

Answer 1

将周长列表转换为 Json 列表，如下所示：

if (this.perimeters != null) {
          data['perimeters'] = this.perimeters!.map((v) => v.toJson()).toList();
        }

Answer 2

这里的工作是将整个 json 响应转换为字符串。将该字符串保存到 sharedprefs 中，然后您可以调用它并使用以下命令对其进行解码：

var response = json.decode(prefs.getString("response");

所以，完整的想法：

prefs.setString("response",json.encode(response.body));

再次将该字符串用作 json 格式：

MyModel model = MyModel.fromJson(json.decode(prefs.getString("response")));

我希望你能从这个想法中找到你需要的东西。

在共享首选项中保存嵌套对象

Save nested objects in shared preferences

sharedpreferences

dart

flutter