flutter json_serializable 的使用

一、配置

1、去根目录 pubspec.yaml 文件中加入 json_annotation、json_serializable、build_runner 等三个依赖，如：

name: flutter_app
description: A new Flutter project.

# The following line prevents the package from being accidentally published to
# pub.dev using `flutter pub publish`. This is preferred for private packages.
publish_to: 'none' # Remove this line if you wish to publish to pub.dev

# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In Android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In iOS, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
version: 1.0.0+1

environment:
  sdk: ">=2.16.2 <3.0.0"

# Dependencies specify other packages that your package needs in order to work.
# To automatically upgrade your package dependencies to the latest versions
# consider running `flutter pub upgrade --major-versions`. Alternatively,
# dependencies can be manually updated by changing the version numbers below to
# the latest version available on pub.dev. To see which dependencies have newer
# versions available, run `flutter pub outdated`.
dependencies:
  flutter:
    sdk: flutter


  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^1.0.2

 # json_serializable 需要依赖的注解 https://github.com/google/json_serializable.dart/tree/master/example
  json_annotation: ^4.4.0


dev_dependencies:
  flutter_test:
    sdk: flutter

  # The "flutter_lints" package below contains a set of recommended lints to
  # encourage good coding practices. The lint set provided by the package is
  # activated in the `analysis_options.yaml` file located at the root of your
  # package. See that file for information about deactivating specific lint
  # rules and activating additional ones.
  flutter_lints: ^1.0.0

 # json 序列化辅助类 https://pub.flutter-io.cn/packages/json_serializable/install
  # https://github.com/google/json_serializable.dart/tree/master/example
  json_serializable: ^6.2.0
  build_runner: ^2.0.0


# For information on the generic Dart part of this file, see the
# following page: https://dart.dev/tools/pub/pubspec

# The following section is specific to Flutter.
flutter:

  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.

uses-material-design: true

  # To add assets to your application, add an assets section, like this:
  # assets:
  #   - images/a_dot_burr.jpeg
  #   - images/a_dot_ham.jpeg

  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.dev/assets-and-images/#resolution-aware.

  # For details regarding adding assets from package dependencies, see
  # https://flutter.dev/assets-and-images/#from-packages

  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a

 # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  # example:
  # fonts:
  #   - family: Schyler
  #     fonts:
  #       - asset: fonts/Schyler-Regular.ttf
  #       - asset: fonts/Schyler-Italic.ttf
  #         style: italic
  #   - family: Trajan Pro
  #     fonts:
  #       - asset: fonts/TrajanPro.ttf
  #       - asset: fonts/TrajanPro_Bold.ttf
  #         weight: 700
  #

 # For details regarding fonts from package dependencies,
  # see https://flutter.dev/custom-fonts/#from-packages

二、编写 demo

1、新建 LiveListData.dart 文件，内容如下：

@JsonSerializable()
class LiveListData {
  late int pageSize;
  late int pageNo;
  late List rows;
  late int total;

  LiveListData();

// 固定格式，不同的类使用不同的mixin即可
  // 这里声明一个工厂构造方法
  factory LiveListData.fromJson(Map json) =>
      $LiveListDataFromJson(json);

  Map toJson() => $LiveListDataToJson(this);

  LiveListData copyWith(
      {int? pageSize, int? pageNo, List? rows, int? total}) {
    return LiveListData()
      ..pageSize = pageSize ?? this.pageSize
      ..pageNo = pageNo ?? this.pageNo
      ..rows = rows ?? this.rows
      ..total = total ?? this.total;
  }

  @override
  String toString() {
    return jsonEncode(this);
  }
}

1）@JsonSerializable() ：表示当前类需要被 json_serializable 处理；
2）part 'LiveListData.g.dart'：这里的 part 表示当前文件（LiveListData.dart）关联 LiveListData.g.dart，其中 LiveListData.g.dart 命名规范是：文件名称.g.dart；

3） _$ResultFromJson ：是 json_serializable 帮我们生成的将 Map 转为实体类的方法，这个方法的命名规则：_$+当前类名+FromJson；
4）_$ResultToJson ：是 json_serializable 帮我们生成的将实体类转为 Map 的方法，这个方法的命名规则：_$+当前类名+ToJson；
5）factory Result.fromJson : 这里是声明了工厂构造函数 fromJson ；

2、去到项目根目录，执行 flutter pub run build_runner build 命令，生成 LiveListData.g.dart 文件

LiveListData $LiveListDataFromJson(Map json) {
    final LiveListData liveListData = LiveListData();
    final int? pageSize = jsonConvert.convert(json['pageSize']);
    if (pageSize != null) {
        liveListData.pageSize = pageSize;
    }
    final int? pageNo = jsonConvert.convert(json['pageNo']);
    if (pageNo != null) {
        liveListData.pageNo = pageNo;
    }
    final List? rows = jsonConvert.convertListNotNull(json['rows']);
    if (rows != null) {
        liveListData.rows = rows;
    }
    final int? total = jsonConvert.convert(json['total']);
    if (total != null) {
        liveListData.total = total;
    }
    return liveListData;
}

Map $LiveListDataToJson(LiveListData entity) {
    final Map data = {};
    data['pageSize'] = entity.pageSize;
    data['pageNo'] = entity.pageNo;
    data['rows'] =  entity.rows.map((v) => v.toJson()).toList();
    data['total'] = entity.total;
    return data;
}