在Flutter项目中，ObjectDb dart中的DateTime解析问题

如何解决在Flutter项目中，ObjectDb dart中的DateTime解析问题

我在下面的飞镖项目中遇到了异常：

E/Flutter (17804): [ERROR:Flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: Instance of 'objectdbException'

我的模型课是：

import 'item.dart';

class User {
  String id;
  String name;
  String mobile;
  String imageUrl;
  String address;
  List<Item> items;
  DateTime createdAt;

  User({
    this.id,this.name,this.mobile,this.imageUrl,this.address,this.items,this.createdAt,});

  Map<String,dynamic> toJson() {
    final Map<String,dynamic> data = new Map<String,dynamic>();
    final List<Map<String,dynamic>> subData = [];
    data['id'] = this.id;
    data['name'] = this.name;
    data['mobile'] = this.mobile;
    data['imageUrl'] = this.imageUrl;
    data['address'] = this.address;
    this.items.forEach((element) {
      subData.add(element.toJson());
    });
    data['items'] = subData;
    data['createdAt'] = this.createdAt;
    //data['createdAt'] = this.createdAt;
    return data;
  }
}

当我从类中删除DateTime createdAt成员时，它工作正常。然后将其存储到db并检索就可以了。但是添加完之后，我得到了上面的异常。

从数据库端检索逻辑是：

User _getUserFromMap(Map<dynamic,dynamic> val) {
      List<Item> items = [];
      if (val['items'] != null) {
        print('Items Type: ${val['items'].runtimeType.toString()}');
        print('Items: ${val['items']}');
        print('Items lenth: ${val['items'].length}');
        items = List.generate(
            val['items'].length,(index) => _getItemFromMap(val['items'][index]));
      }
      print('Use date: ${val['createdAt']}');
      User user = User(
        id: val['id'],name: val['name'],mobile: val['mobile'],address: val['address'],imageUrl: val['imageUrl'],items: items,createdAt: DateTime.Now(),);
      return user;
  }

任何帮助表示赞赏。 谢谢！