This is where the error comes from. "Null". In the console I received error like "type 'Null' is not a subtype of type 'String'"

 class UserPreferences {
  static late SharedPreferences _preferences;

  static const _keyUser = 'user';
  static const myUser = User(
    imagePath: "https://assets.teenvogue.com/photos/5591a26d33df629d5e314870/master/w_420,h_630,c_limit/08-jacob-morton.jpg",
    name: "Deva",
    email: "[email protected]",
    mobile: "9998887776",
    address: "2, Park street, Chennai",
    userid: "1",
    isDarkMode: false,
  );

  static Future init() async =>
      _preferences = await SharedPreferences.getInstance();

  static Future setUser(User user) async {
    final json = jsonEncode(user.toJson());

    await _preferences.setString(_keyUser, json);
  }

  static User getUser(){
    final json = _preferences.getString(_keyUser);

    return json == null ?  myUser : User.fromJson(jsonDecode(json));
  }
}
    }

Json getUser

Included the getUser class for clarification. Do we need to add dependecies or adds an additional property

class User{
  final String imagePath;
  final String name;
  final String email;
  final String mobile;
  final String address;
  final String userid;
  final bool isDarkMode;

  const User ({
    required this.imagePath,
    required this.name,
    required this.email,
    required this.mobile,
    required this.address,
    required this.userid,
    required this.isDarkMode,
});

  User copy({
    String? imagePath,
    String? name,
    String? email,
    String? mobile,
    String? address,
    String? userid,
    bool? isDarkMode,
}) =>
  User (
    imagePath: imagePath ?? this.imagePath,
    name:  name ?? this.name,
    email: email ?? this.email,
    mobile:  mobile ?? this.mobile,
    address: address ?? this.address,
    userid: userid ?? this.userid,
    isDarkMode: isDarkMode ?? this.isDarkMode,
  );

  static User fromJson(Map<String, dynamic>json) => User(
    imagePath: json ["imagePath"],
    name: json ["name"],
    email: json ["email"],
    mobile:  json ["mobile"],
    address: json ["address"],
    userid: json ["userid"],
    isDarkMode: json ["isDarkMode"],
  );

  Map<String, dynamic> toJson() => {
    "imagePath": imagePath,
    "name": name,
    "email": email,
    "mobile": mobile,
    "address": address,
    "isDarkMode": isDarkMode,
  };
}

Thanks in Advance for helping..
I am new to flutter and suggestions are welcome.

CodePudding user response：

You should try to give fallback values in the fromJson method in case some are null, like this

  static User fromJson(Map<String, dynamic>json) => User(
    imagePath: json ["imagePath"] ?? '',
    name: json ["name"] ?? '',
    email: json ["email"] ?? '',
    mobile:  json ["mobile"] ?? '',
    address: json ["address"] ?? '',
    userid: json ["userid"] ?? '',
    isDarkMode: json ["isDarkMode"] ?? false,
  );