如何将复杂（嵌套）对象解析为 JSON 并在 Flutter 中使用 HTTP 将其发送到服务器？答案

【问题标题】：How to parse a complex(nested) object to JSON and send it to server using HTTP in flutter?如何将复杂（嵌套）对象解析为 JSON 并在 Flutter 中使用 HTTP 将其发送到服务器？
【发布时间】：2019-12-30 21:35:35
【问题描述】：

您好，我有一个类，其中嵌套了其他类。我想将此对象转换为 JSON 字符串并将其发送到服务器。

我已经从堆栈溢出和谷歌搜索中尝试了很多答案。不足以回答我的问题。

感谢任何帮助。

这是我的模型

class Place {
   String name;
   String description;
   List<PhoneNumber> phoneNumbers;
   List<String> tags;
   GPSCoordinante gpsCoordinates;
   List<Service> services;
   List<Album> albums;
   SocialMedia socialMedia;
   List<Comment> comments;
   List<String> imageURLArray;
   int rating;
   int shares;
   int favorites;
   int views;
   String category;
   String subcategory;
   WorkingHour workingHours;
   bool deleted;
   double distanceToUser;
   bool isApproved;
   String address;
   List<String> coverImages;

  Place({
    this.name,
    this.description,
    this.phoneNumbers,
    this.tags,
    this.gpsCoordinates,
    this.services,
    this.albums,
    this.socialMedia,
    this.comments,
    this.imageURLArray,
    this.rating,
    this.shares,
    this.favorites,
    this.views,
    this.category,
    this.subcategory,
    this.workingHours,
    this.deleted,
    this.distanceToUser,
    this.isApproved ,
    this.address,
    this.coverImages,
});

  factory Place.fromJson(Map<String, dynamic> json) {


    List phoneNumbersJsonList = json['phoneNumbers'] as List;
    List<PhoneNumber> parsedPhoneNumbers = phoneNumbersJsonList.map((value) => PhoneNumber.fromJson(value)).toList();

    List servicesJsonList = json['services'] as List;
    List<Service> parsedServices = servicesJsonList.map((value) => Service.fromJson(value)).toList();

    List walbumsJsonList = json['albums'] as List;
    List<Album> parsedAlbums = walbumsJsonList.map((value) => Album.fromJson(value)).toList();

    List commentsJsonList = json['comments'] as List;
    List<Comment> parsedComments = commentsJsonList.map((value) => Comment.fromJson(value)).toList();


    return Place(
        name: json['name'],
        description: json['description'],
        phoneNumbers:  parsedPhoneNumbers,
        gpsCoordinates: json['gpsCoordinates'],
        services: parsedServices,
        albums: parsedAlbums,
        socialMedia: json['socialMedia'],
        comments: parsedComments,
        imageURLArray: json['imageURLArray'],
        rating: json['rating'],
        shares : json['shares'],
        favorites: json['favorites'],
        category: json['category'],
        subcategory: json['subcategory'],
        workingHours: json['workingHours'],
        deleted: json['deleted'],
        isApproved: json['isApproved'],
        address: json['address'],
        coverImages: json['coverImages'],
    );

  }

   Map toMap() {
     var map = new Map<String, dynamic>();
     map["name"] = name;
     map["description"] = description;
     map["services"] = services;
     map["albums"] = albums;
     map["comments"] = comments;
     map["imageURLArray"] = imageURLArray;
     map["rating"] = rating;
     map["shares"] = shares;
     map["favorites"] = favorites;
     map["category"] = category;
     map["subcategory"] = subcategory;
     map["workingHours"] = workingHours;
     map["deleted"] = deleted;
     map["isApproved"] = isApproved;
     map["address"] = address;
     map["coverImages"] = coverImages;


     return map;
   }


}

class PhoneNumber {
   int phoneNumber;
   String owner;

  PhoneNumber({
    this.phoneNumber,
    this.owner
});

  factory PhoneNumber.fromJson(Map<String, dynamic> json) {
    return PhoneNumber(
      phoneNumber: json['phoneNumber'],
      owner: json['owner'],
    );
  }

   Map toMap() {
     var map = new Map<String, dynamic>();
     map["phoneNumber"] = phoneNumber;
     map["owner"] = owner;

     return map;
   }
}

class GPSCoordinante {
   double longitude;
   double latitude;

  GPSCoordinante({
    this.longitude,
    this.latitude
});

  factory GPSCoordinante.fromJson(Map<String, dynamic> json) {
    return GPSCoordinante(
      longitude: json['longitude'],
      latitude: json['latitude'],
    );
  }

   Map toMap() {
     var map = new Map<String, dynamic>();
     map["longitude"] = longitude;
     map["latitude"] = latitude;

     return map;
   }
}


class Service {

  String name;
  String description;

  Service({
    this.name,
    this.description
  });

  factory Service.fromJson(Map<String, dynamic> json) {
    return Service(
      name: json['name'],
      description: json['description'],
    );
  }

  Map toMap() {
    var map = new Map<String, dynamic>();
    map["name"] = name;
    map["description"] = description;

    return map;
  }
}

class Album {
   String name;
   String nameEn;
   List<Item> items;
   bool isAutoConvertToUSDEnabled;
   bool isAllItemsDeliveryEnabled;

  Album({
    this.name,
    this.nameEn,
    this.items,
    this.isAutoConvertToUSDEnabled,
    this.isAllItemsDeliveryEnabled
});

  factory Album.fromJson(Map<String, dynamic> json) {

    List itemsJsonList = json['items'] as List;
    List<Item> parsedItems = itemsJsonList.map((value) => Item.fromJson(value)).toList();

    return Album(
      name: json['name'],
      nameEn: json['nameEn'],
      items: parsedItems,
      isAutoConvertToUSDEnabled: json['isAutoConvertToUSDEnabled'],
      isAllItemsDeliveryEnabled: json['isAllItemsDeliveryEnabled']

    );
  }

   Map toMap() {
     var map = new Map<String, dynamic>();
     map["name"] = name;
     map["nameEn"] = nameEn;
     map["items"] = items;
     map["isAutoConvertToUSDEnabled"] = isAutoConvertToUSDEnabled;
     map["isAllItemsDeliveryEnabled"] = isAllItemsDeliveryEnabled;

     return map;
   }
}

class Item{
   List<String> imageVariants;
   String name;
   String nameEn;
   bool isAutoConvertNameToEnglishEnabled;
   List<String> tags;
   int priceIQD;
   double priceUSD;
   String description;
   bool isDeliveryAvailable;
   bool isDinarAutomaticallyConvertedToDollar;
   int itemIndex;
   int albumIndex;
   bool isDeleted;

  Item({
    this.imageVariants,
    this.name,
    this.nameEn,
    this.isAutoConvertNameToEnglishEnabled,
    this.tags,
    this.priceIQD,
    this.priceUSD,
    this.description,
    this.isDeliveryAvailable,
    this.isDinarAutomaticallyConvertedToDollar,
    this.itemIndex,
    this.albumIndex,
    this.isDeleted
});

  factory Item.fromJson(Map<String, dynamic> json) {
    return Item(
      imageVariants: json['imageVariants'],
      name: json['name'],
      nameEn: json['nameEn'],
      isAutoConvertNameToEnglishEnabled: json['isAutoConvertNameToEnglishEnabled'],
      tags: json['tags'],
      priceIQD: json['priceIQD'],
      priceUSD: json['priceUSD'],
      description: json['description'],
      isDeliveryAvailable: json['isDeliveryAvailable'],
      isDinarAutomaticallyConvertedToDollar: json['isDinarAutomaticallyConvertedToDollar'],
      albumIndex: json['albumIndex'],
      itemIndex: json['itemIndex'],
      isDeleted: json['isDeleted'],

    );
  }

   Map toMap() {
     var map = new Map<String, dynamic>();
     map["imageVariants"] = imageVariants;
     map["name"] = name;
     map["nameEn"] = nameEn;
     map["isAutoConvertNameToEnglishEnabled"] = isAutoConvertNameToEnglishEnabled;
     map["tags"] = tags;
     map["priceIQD"] = priceIQD;
     map["priceUSD"] = priceUSD;
     map["description"] = description;
     map["isDeliveryAvailable"] = isDeliveryAvailable;
     map["isDinarAutomaticallyConvertedToDollar"] = isDinarAutomaticallyConvertedToDollar;
     map["albumIndex"] = albumIndex;
     map["itemIndex"] = itemIndex;
     map["isDeleted"] = isDeleted;

     return map;
   }

}


class Comment{
   String user;
   String userId;
   String text;
   DateTime dateTime;

  Comment({
   this.user,
   this.userId,
   this.text,
   this.dateTime
});

  factory Comment.fromJson(Map<String, dynamic> json) {
    return Comment(
      user: json['user'],
      userId: json['userId'],
      text: json['text'],
      dateTime: json['dateTime'],

    );
  }

   Map toMap() {
     var map = new Map<String, dynamic>();
     map["user"] = user;
     map["userId"] = userId;
     map["text"] = text;
     map["dateTime"] = dateTime;
     return map;
   }
}

class WorkingHour{
   String openingHour;
   String openingHourAmOrPm;
   String closingHour;
   String closingHourAmOrPm;

  WorkingHour({
    this.openingHour,
    this.openingHourAmOrPm,
    this.closingHour,
    this.closingHourAmOrPm
});

  factory WorkingHour.fromJson(Map<String, dynamic> json) {
    return WorkingHour(
      openingHour: json['openingHour'],
      openingHourAmOrPm: json['openingHourAmOrPm'],
      closingHour: json['closingHour'],
      closingHourAmOrPm: json['closingHourAmOrPm'],

    );
  }

   Map toMap() {
     var map = new Map<String, dynamic>();
     map["openingHour"] = openingHour;
     map["openingHourAmOrPm"] = openingHourAmOrPm;
     map["closingHour"] = closingHour;
     map["closingHourAmOrPm"] = closingHourAmOrPm;
     return map;
   }
}

class SocialMedia {
  String facebook ;
  String instagram;
  String youTube;
  String snapChat;
  String twitter;
  String googlePlus;
  String pinterest;

  SocialMedia({
    this.facebook,
    this.instagram,
    this.youTube,
    this.snapChat,
    this.twitter,
    this.googlePlus,
    this.pinterest
});

  factory SocialMedia.fromJson(Map<String, dynamic> json) {
    return SocialMedia(
      facebook: json['facebook'],
      instagram: json['instagram'],
      youTube: json['youTube'],
      snapChat: json['snapChat'],
      twitter: json['twitter'],
      googlePlus: json['googlePlus'],
      pinterest: json['pinterest'],


    );
  }

  Map toMap() {
    var map = new Map<String, dynamic>();
    map["facebook"] = facebook;
    map["instagram"] = instagram;
    map["youTube"] = youTube;
    map["twitter"] = twitter;
    map["snapChat"] = snapChat;
    map["googlePlus"] = googlePlus;
    map["pinterest"] = pinterest;

    return map;
  }
}

我正在尝试将此 Place 对象发送到服务器：

 Place place = Place(
      name: 'some name',
      description: 'some description',
      phoneNumbers: [PhoneNumber(phoneNumber: 125252525, owner: 'ali')],
      tags: ['some tag 2', 'some tag 2'],
      gpsCoordinates: GPSCoordinante(latitude: 11332, longitude: 13415),
      services: [Service(name: 'some service', description: 'some description')],
      albums: [
        Album(
            name: 'some album name',
            nameEn: 'someEN name',
            items: [
              Item(
                  name: 'some item name',
                  imageVariants: ['a;lgjlagj', 'ag;ja;gj;ag'],
                  nameEn: 'some en name',
                  isAutoConvertNameToEnglishEnabled: true,
                  tags: ['aggagag'],
                  priceIQD: 32425,
                  priceUSD: 252525,
                  description: 'agkgl;aj g;g ja;g ',
                  isDeliveryAvailable: true,
                  isDinarAutomaticallyConvertedToDollar: true,
                  itemIndex: 1,
                  albumIndex: 2)
            ],
            isAutoConvertToUSDEnabled: true,
            isAllItemsDeliveryEnabled: false)
      ],
      socialMedia: SocialMedia(facebook: 'facebook url'),
      comments: [
        Comment(
            user: 'some user',
            userId: '324-2-5-25',
            text: 'some comment',
            dateTime: DateTime.now())
      ],
      imageURLArray: ['some url'],
      rating: 0,
      shares: 0,
      favorites: 0,
      views: 0,
      category: 'sdagagasga;lgjaa;lgj',
      subcategory: 'as;glgjasl;gjas;lgkj',
      workingHours: WorkingHour(
          openingHour: '11', openingHourAmOrPm: 'am', closingHour: '11:00'),
      deleted: false,
      distanceToUser: 225252,
      isApproved: false,
      address: "some adress",
      coverImages: ['image one', 'image 2']);

我在使用json.encode(place) 时不断出错；或json.encode(place.toMap()) 像这样

将对象转换为可编码对象失败：实例 “服务”

如何才能做到这一点？

【问题讨论】：

标签： json http flutter dart encode

【解决方案1】：

您似乎不需要编写太多代码来将您的类编码和解码为 JSON 字符串。为了避免大量冗余并让您的生活更轻松，请使用以下解决方案：

事情是这样的：

首先在你的 pubspec.yaml 中依赖这些库：

dependencies:
  # Your other regular dependencies here
  json_annotation: ^2.0.0

dev_dependencies:
  # Your other dev_dependencies here
  build_runner: ^1.0.0
  json_serializable: ^2.0.0

然后在您拥有所有模型类的文件中将其添加到顶部：

import 'package:json_annotation/json_annotation.dart';
part 'user.g.dart';

而不是part 'user.g.dart'; 中的用户使用模型类所在文件的名称。在我的例子中是model.dart，所以它变成：

part 'model.g.dart';

这给出了一条红色波浪线：

这很好，你需要做的是在项目根目录中的终端中运行以下命令：

flutter pub run build_runner watch

这样做是生成part 'model.g.dart'; 文件，这样您就不会再看到红色下划线了。它会监视你的模型（包含你的模型的文件，在我的例子中是 models.dart 文件），看看你的类中的变量或字段是否有任何变化。

如果您进行任何更改，它将自动重新生成将模型从 JSON 转换为 JSON 所需的代码，这意味着需要（json decode and encode）。

然后，您必须将此行添加到模型文件（在我的例子中为 models.dart）中每个类的上方。

所以把它添加到每个类上面的行：

@JsonSerializable(explicitToJson: true)

例如这样：

@JsonSerializable(explicitToJson: true)
class Place{ some fields};

在你的类定义中，你必须将它添加到每个类中：

factory Place.fromJson(Map<String, dynamic> json) => _$PlaceFromJson(json);
  Map<String, dynamic> toJson() => _$PlaceToJson(this);

当然，您必须将变量 _$PlaceFromJson(json) 和 _$PlaceToJson(this) 更改为反映您的班级名称的内容。例如，如果我有一个 PhoneNumber 类，我必须将这些两个变量分别更改为 _$PhoneNumberFromJson(json) 和 _$PhoneNumberToJson(this)。

现在你只需要为你的模型创建一个对象，例如 Place 类，然后将它传递给 jsonEndcode 或 jsonDecode，如下所示：

放置地点 = 地点（ name : "某个名字", 描述：“一些描述” );

var placeEncoded = jsonEncode(place);
print(placeEncoded);

var placeDecoded = jsonDecode(place);
print(placeDecoded );

这就是你需要做的。

官方文档可以在这个页面上找到： https://flutter.dev/docs/development/data-and-backend/json#code-generation

这是我的 model.dart 现在的样子：

import 'package:json_annotation/json_annotation.dart';
part 'models.g.dart';


@JsonSerializable(explicitToJson: true)
class Place {
   String name;
   String description;
   List<PhoneNumber> phoneNumbers;
   List<String> tags;
   GPSCoordinante gpsCoordinates;
   List<Service> services;
   List<Album> albums;
   SocialMedia socialMedia;
   List<Comment> comments;
   List<String> imageURLArray;
   int rating;
   int shares;
   int favorites;
   int views;
   String category;
   String subcategory;
   WorkingHour workingHours;
   bool deleted;
   double distanceToUser;
   bool isApproved;
   String address;
   List<String> coverImages;

  Place({
    this.name,
    this.description,
    this.phoneNumbers,
    this.tags,
    this.gpsCoordinates,
    this.services,
    this.albums,
    this.socialMedia,
    this.comments,
    this.imageURLArray,
    this.rating,
    this.shares,
    this.favorites,
    this.views,
    this.category,
    this.subcategory,
    this.workingHours,
    this.deleted,
    this.distanceToUser,
    this.isApproved ,
    this.address,
    this.coverImages,
});

  factory Place.fromJson(Map<String, dynamic> json) => _$PlaceFromJson(json);
  Map<String, dynamic> toJson() => _$PlaceToJson(this);


}

@JsonSerializable(explicitToJson: true)
class PhoneNumber {
   int phoneNumber;
   String owner;

  PhoneNumber({
    this.phoneNumber,
    this.owner
});


   factory PhoneNumber.fromJson(Map<String, dynamic> json) => _$PhoneNumberFromJson(json);
   Map<String, dynamic> toJson() => _$PhoneNumberToJson(this);
}

@JsonSerializable(explicitToJson: true)
class GPSCoordinante {
   double longitude;
   double latitude;

  GPSCoordinante({
    this.longitude,
    this.latitude
});

   factory GPSCoordinante.fromJson(Map<String, dynamic> json) => _$GPSCoordinanteFromJson(json);
   Map<String, dynamic> toJson() => _$GPSCoordinanteToJson(this);

}



@JsonSerializable(explicitToJson: true)
class Service {

  String name;
  String description;

  Service({
    this.name,
    this.description
  });

  factory Service.fromJson(Map<String, dynamic> json) => _$ServiceFromJson(json);
  Map<String, dynamic> toJson() => _$ServiceToJson(this);
}

@JsonSerializable(explicitToJson: true)
class Album {
   String name;
   String nameEn;
   List<Item> items;
   bool isAutoConvertToUSDEnabled;
   bool isAllItemsDeliveryEnabled;

  Album({
    this.name,
    this.nameEn,
    this.items,
    this.isAutoConvertToUSDEnabled,
    this.isAllItemsDeliveryEnabled
});


   factory Album.fromJson(Map<String, dynamic> json) => _$AlbumFromJson(json);
   Map<String, dynamic> toJson() => _$AlbumToJson(this);

}

@JsonSerializable(explicitToJson: true)
class Item{
   List<String> imageVariants;
   String name;
   String nameEn;
   bool isAutoConvertNameToEnglishEnabled;
   List<String> tags;
   int priceIQD;
   double priceUSD;
   String description;
   bool isDeliveryAvailable;
   bool isDinarAutomaticallyConvertedToDollar;
   int itemIndex;
   int albumIndex;
   bool isDeleted;

  Item({
    this.imageVariants,
    this.name,
    this.nameEn,
    this.isAutoConvertNameToEnglishEnabled,
    this.tags,
    this.priceIQD,
    this.priceUSD,
    this.description,
    this.isDeliveryAvailable,
    this.isDinarAutomaticallyConvertedToDollar,
    this.itemIndex,
    this.albumIndex,
    this.isDeleted
});

   factory Item.fromJson(Map<String, dynamic> json) => _$ItemFromJson(json);
   Map<String, dynamic> toJson() => _$ItemToJson(this);

}


@JsonSerializable(explicitToJson: true)
class Comment{
   String user;
   String userId;
   String text;
   DateTime dateTime;

  Comment({
   this.user,
   this.userId,
   this.text,
   this.dateTime
});

   factory Comment.fromJson(Map<String, dynamic> json) => _$CommentFromJson(json);
   Map<String, dynamic> toJson() => _$CommentToJson(this);

}

@JsonSerializable(explicitToJson: true)
class WorkingHour{
   String openingHour;
   String openingHourAmOrPm;
   String closingHour;
   String closingHourAmOrPm;

  WorkingHour({
    this.openingHour,
    this.openingHourAmOrPm,
    this.closingHour,
    this.closingHourAmOrPm
});

   factory WorkingHour.fromJson(Map<String, dynamic> json) => _$WorkingHourFromJson(json);
   Map<String, dynamic> toJson() => _$WorkingHourToJson(this);

}

@JsonSerializable(explicitToJson: true)
class SocialMedia {
  String facebook ;
  String instagram;
  String youTube;
  String snapChat;
  String twitter;
  String googlePlus;
  String pinterest;

  SocialMedia({
    this.facebook,
    this.instagram,
    this.youTube,
    this.snapChat,
    this.twitter,
    this.googlePlus,
    this.pinterest
});

  factory SocialMedia.fromJson(Map<String, dynamic> json) => _$SocialMediaFromJson(json);
  Map<String, dynamic> toJson() => _$SocialMediaToJson(this);

}

当不必要的编码被丢弃并且不再使用时，我喜欢它。这就是我真正喜欢颤振的原因。

保重。

【讨论】：

explicitToJson: 是的，这就是我需要的。谢谢。

【解决方案2】：

您应该使用 BuiltValue 库 (https://github.com/google/built_value.dart)。

在开始使用该技术之前，您需要学习一天的时间。

但在简历中，您的课程将像上面的课程一样，您必须为每个复杂的课程创建一个类似的课程，例如 PhoneNumber，...：

import 'package:built_collection/built_collection.dart';
import 'package:built_value/built_value.dart';
import 'package:built_value/serializer.dart';
import 'package:wallet/models/transaction.dart';

import 'json_serializer.dart';

part 'place.g.dart';

abstract class Place
    implements Built<Place, PlaceBuilder>, JsonSerializer {


  factory Place([PlaceBuilder updates(PlaceBuilder builder)]) =
      _$Place;

  Place._();

  factory Place.initState() {
    return Place((b) {
      b..name = "";

      return b;
    });
  }
  @nullable
  String get name;

  @nullable
  String get description;

  @nullable
  BuiltList<PhoneNumber> get phoneNumbers;


  static Serializer<Place> get serializer => _$place;


}

创建类之后，您必须定义一个 serializer.dart 类，您可以指定所有可以序列化的对象。请注意，对于定义中使用的每个 BuiltList，您必须为其创建一个工厂：

    part 'serializers.g.dart';

    @SerializersFor(<Type>[
      Place
    ])
    final Serializers serializers = (_$serializers.toBuilder()
          ..addPlugin(StandardJsonPlugin())
..addBuilderFactory(phoneNumberList.fullType, phoneNumberList.function)
        .build();

ListBuilderFactory<PhoneNumber> phoneNumberList = ListBuilderFactory<PhoneNumber>();

在最后一刻，您必须生成文件 .g.dart。使用以下命令：

flutter packages pub run build_runner build --delete-conflicting-outputs

最后，要解码项目中的 json，请调用：

var body = jsonDecode(jsonPlaces);
        Place places = serializers.deserialize(
          body,
          specifiedType: const FullType(Place),
        );

【讨论】：

非常感谢 Roger 抽出宝贵时间撰写如此详细的答案。虽然我决定采用更简单的解决方案。