Question

我有这个模型

class Trail {
    List<CusomPosition> markers;
    List<Vote> voteList;
    ...}

我已经定义了表决和CustomPosition。所有这些类都具有@JsonSerializable批注，并且是它们各自的部分'class.g.dart'的一部分；文件。

当我运行命令时：

flutter pub run build_runner build

一切正常，但是当我尝试在Firestore上添加实例时

Firestore.instance.collection("trails").add(finalTrail.toJson());

我收到此错误：

Unhandled Exception: Invalid argument: Instance of 'Vote'

如果我打印finalTrail.toJson（），我会得到：

votesList: [Instance of 'Vote']

我该怎么做才能正确转换它？

编辑：这是我的足迹的一部分。g.dart

markers: (json['markers'] as List)
      ?.map((e) => e == null
          ? null
          : CustomPosition.fromJson(e as Map<String, dynamic>))
      ?.toList(),
  votesList: (json['votesList'] as List)
      ?.map((e) =>
          e == null ? null : Vote.fromJson(e as Map<String, dynamic>))
      ?.toList(),

Vote.fromJson和CustomPosition.fromJson都存在（它们是通过运行命令创建的）

Answer 1

也许此代码可以为您提供帮助？

import 'dart:convert';

import 'json_objects.dart';

void main() {
  var json = jsonDecode(_data) as Map<String, dynamic>;
  var finalTrail = Trail.fromJson(json);
  print(finalTrail.markers[0].myPosition);
  print(finalTrail.voteList[0].myVote);

  // Firestore.instance.collection("trails").add(finalTrail.toJson());
  print(finalTrail.toJson());
}

var _data = '{"markers":[{"myPosition":1}],"voteList":[{"myVote":41}]}';

1
41
{markers: [{myPosition: 1}], voteList: [{myVote: 41}]}

JSON数据模型：

class CustomPosition {
  final int myPosition;

  CustomPosition({this.myPosition});

  factory CustomPosition.fromJson(Map<String, dynamic> json) {
    return CustomPosition(
      myPosition: json['myPosition'] as int,
    );
  }

  Map<String, dynamic> toJson() {
    return {
      'myPosition': myPosition,
    };
  }
}

class Trail {
  final List<CustomPosition> markers;
  final List<Vote> voteList;

  Trail({this.markers, this.voteList});

  factory Trail.fromJson(Map<String, dynamic> json) {
    return Trail(
      markers:
          _toObjectList(json['markers'], (e) => CustomPosition.fromJson(e)),
      voteList: _toObjectList(json['voteList'], (e) => Vote.fromJson(e)),
    );
  }

  Map<String, dynamic> toJson() {
    return {
      'markers': _fromList(markers, (e) => e.toJson()),
      'voteList': _fromList(voteList, (e) => e.toJson()),
    };
  }
}

class Vote {
  final int myVote;

  Vote({this.myVote});

  factory Vote.fromJson(Map<String, dynamic> json) {
    return Vote(
      myVote: json['myVote'] as int,
    );
  }

  Map<String, dynamic> toJson() {
    return {
      'myVote': myVote,
    };
  }
}

List _fromList(data, Function(dynamic) toJson) {
  if (data == null) {
    return null;
  }
  var result = [];
  for (var element in data) {
    var value;
    if (element != null) {
      value = toJson(element);
    }
    result.add(value);
  }
  return result;
}

List<T> _toObjectList<T>(data, T Function(Map<String, dynamic>) fromJson) {
  if (data == null) {
    return null;
  }
  var result = <T>[];
  for (var element in data) {
    T value;
    if (element != null) {
      value = fromJson(element as Map<String, dynamic>);
    }
    result.add(value);
  }
  return result;
}

/*
Trail:
  markers: List<CustomPosition>
  voteList: List<Vote>

CustomPosition:
  myPosition: int

Vote:
  myVote: int
*/

当我尝试将自定义对象解析为json时，Firestore（Flutter）引发异常

1 个答案: