这是我的User类:
import 'package:geocoder/model.dart';
import 'package:json_annotation/json_annotation.dart';
import './resource.dart';
part 'user.g.dart';
@JsonSerializable()
class User extends Resource {
User(this.email, this.name);
String email;
String name;
List<Address> addresses;
factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
Map<String, dynamic> toJson() => _$UserToJson(this);
}
构造函数返回的类型“ Address”不是预期的类型“ UserAddress”。dart(invalid_cast_new_expr)
在命名的构造函数UserAddress.fromJson中:
import 'package:geocoder/geocoder.dart';
import 'package:json_annotation/json_annotation.dart';
part 'user-address.g.dart';
@JsonSerializable()
class UserAddress extends Address {
UserAddress();
factory UserAddress.fromJson(Map<String, dynamic> json) =>
Address.fromMap(json);
Map<String, dynamic> toJson() => this.toMap();
}
请给我一些选择,以实现与地图之间的解析。
答案 0 :(得分:1)
如果我答对了,您想用自己的装饰图书馆的课。您可以使用@JsonKey
注释来设置(en)解码库的Address
对象的函数。
import 'dart:convert';
import 'package:geocoder/geocoder.dart';
import 'package:json_annotation/json_annotation.dart';
part 'user_address.g.dart';
@JsonSerializable()
class UserAddress {
UserAddress(this.address, this.oneMoreField);
@JsonKey(fromJson: _addressFromJson, toJson: _addressToJson)
final Address address;
final int oneMoreField;
factory UserAddress.fromJson(Map<String, dynamic> json) => _$UserAddressFromJson(json);
Map<String, dynamic> toJson() => _$UserAddressToJson(this);
}
String _addressToJson(Address address) => jsonEncode(address.toMap());
Address _addressFromJson(String json) => Address.fromMap(jsonDecode(json));
用法示例:
final testUserAddress = UserAddress(Address(
addressLine: 'test',
coordinates: Coordinates(10, 20)
), 1);
final json = testUserAddress.toJson();
print(json);
final decoded = UserAddress.fromJson(json);
打印:
{address: {"coordinates":{"latitude":10.0,"longitude":20.0},"addressLine":"test","countryName":null,"countryCode":null,"featureName":null,"postalCode":null,"locality":null,"subLocality":null,"adminArea":null,"subAdminArea":null,"thoroughfare":null,"subThoroughfare":null}, oneMoreField: 1}
如您所见,所有嵌套对象都被正确编码。
UPD :通过继承进行操作时,您必须将所有基类的字段传递给超级构造函数,并使用@JsonKey
批注覆盖嵌套对象的字段:
@JsonSerializable()
class UserAddress extends Address {
UserAddress({String addressLine, String countryName, this.coordinates, this.oneMoreField})
: super(addressLine: addressLine, countryName: countryName);
@override
@JsonKey(fromJson: _coordinatesFromJson, toJson: _coordinatesToJson)
final Coordinates coordinates;
final int oneMoreField;
factory UserAddress.fromJson(Map<String, dynamic> json) => _$UserAddressFromJson(json);
Map<String, dynamic> toJson() => _$UserAddressToJson(this);
}
String _coordinatesToJson(Coordinates coordinates) => jsonEncode(coordinates.toMap());
Coordinates _coordinatesFromJson(String json) => Coordinates.fromMap(jsonDecode(json));
结果:
{addressLine: test, countryName: null, coordinates: {"latitude":10.0,"longitude":20.0}, oneMoreField: 1}
但是在这种情况下,我建议对继承使用合成。