flutter - 在 flutter 中序列化对象列表并使用共享首选项保存它时出现问题

Question

我一直在尝试保存类型为 Contact 的列表(这是来自 contacts_service 的类)通过使用 toJosn 对其进行序列化来打包和 fromJson然后将其保存为 String在Shared Preferences

到&从Josn:

 Contact.fromJson(Map<String, dynamic> json):
        identifier = json['identifier'],
        displayName = json['displayName'],
        givenName = json['givenName'],
        middleName = json['middleName'],
        prefix = json['prefix'],
        suffix = json['suffix'],
        familyName = json['familyName'],
        company = json['company'],
        avatar = json['avatar'],
        androidAccountType = json['androidAccountType'],
        jobTitle = json['jobTitle'],
        androidAccountTypeRaw = json['androidAccountTypeRaw'],
        androidAccountName = json['androidAccountName'],
        emails = json['emails'], phones = json['phones'],
        postalAddresses = json['postalAddresses'],
        birthday = json['birthday'];

  Map<String, dynamic> toJson() => {
    'identifier':identifier,
    'displayName':displayName,
    'givenName':givenName,
    'middleName':middleName,
    'prefix':prefix,
    'suffix':suffix,
    'familyName':familyName,
    'company':company,
    'avatar':avatar,
    'jobTitle':jobTitle,
    'androidAccountTypeRaw':androidAccountTypeRaw,
    'androidAccountName':androidAccountName,
    'emails':emails,
    'phones':phones,
    'postalAddresses':postalAddresses,
    'birthday':birthday,
    'androidAccountType':androidAccountType};

保存和加载:

  void saveContacts() async{
    SharedPreferences prefs = await SharedPreferences.getInstance();
    final String List = json.encode(contacts.map((contact) => contact.toJson()));
    await prefs.setString('contactList', List);
  }

  void loadConatcs() async{
    SharedPreferences prefs = await SharedPreferences.getInstance();
    final String saved = prefs.getString('contactList');
    final List<dynamic> decoded = json.decode(saved);
    contacts = decoded.map((contact) => Contact.fromJson(contact));
  }

但我遇到了一个错误 Converting object to an encodable object failed: Instance of 'MappedListIterable<dynamic, Item>'

另请注意，这是我第一次尝试序列化和对象，因此可能遗漏了 to 中的一些内容& fromJosn

编辑:

我也试过使用 toEncodable

final String List = jsonEncode(contacts, toEncodable: (c)=> c.toJson());        

但它会返回一个异常:type 'MappedListIterable<dynamic, Contact>' is not a subtype of type 'List<Contact>'

Answer 1

这可能会解决您的问题:

var contacts = decoded.map((c) => Contact.fromJson(Map<String, dynamic>.from(c)));