前言

使用 json_annotation 框架实现json字符串序列化和反序列化

框架官方地址：json_serializable

一、引入依赖：在pubspec.yaml中添加

dependencies:json_annotation: ^4.8.1dev_dependencies:build_runner: ^2.3.3json_serializable: ^6.6.0

二、使用过程

数据源：

{"id": 1,"name": "John","email": "john@example.com","phone_numbers": [{"type": "home","number": "1234567890"},{"type": "work","number": "0987654321"}]
}

创建数据模型：

// 引入依赖
import 'package:json_annotation/json_annotation.dart';// 指定此类的代码生成文件(格式：part '类名.g.dart';)
part 'Person.g.dart';// 添加序列化标注
@JsonSerializable()
class Person {int id;String name;String email;// 使用别名@JsonKey(name: "phone_numbers")List<PhoneNumber> phoneNumbers;Person(this.id, this.name, this.email, this.phoneNumbers);// 添加反序列化方法(格式：factory 类名.fromJson(Map<String, dynamic> json) => _$类名FromJson(json);)factory Person.fromJson(Map<String,dynamic> json) => _$PersonFromJson(json);// 添加序列化方法(格式：Map<String, dynamic> toJson() => _$类名ToJson(this);)Map<String,dynamic> toJson() => _$PersonToJson(this);
}@JsonSerializable()
class PhoneNumber {String type;String number;PhoneNumber(this.type, this.number);factory PhoneNumber.fromJson(Map<String,dynamic> json) => _$PhoneNumberFromJson(json);Map<String,dynamic> toJson() => _$PhoneNumberToJson(this);
}

使用命令生成对应的.g.dart内容

在android studio的Terminal终端使用如下命令：

flutter pub run build_runner build

命令生成过程：

PS D:\AndroidStudioProjects\github_client_app> flutter pub run build_runner build
Deprecated. Use `dart run` instead.
Building package executable... (5.9s)
Built build_runner:build_runner.
[INFO] Generating build script completed, took 252ms
[INFO] Reading cached asset graph completed, took 73ms
[INFO] Checking for updates since last build completed, took 685ms
[INFO] Running build completed, took 19.0s
[INFO] Caching finalized dependency graph completed, took 87ms
[INFO] Succeeded after 19.1s with 602 outputs (606 actions)
PS D:\AndroidStudioProjects\github_client_app> flutter pub run build_runner build
Deprecated. Use `dart run` instead.
[INFO] Generating build script completed, took 252ms
[INFO] Reading cached asset graph completed, took 193ms
[INFO] Checking for updates since last build completed, took 683ms
[INFO] Running build completed, took 10.1s
[INFO] Caching finalized dependency graph completed, took 86ms
[INFO] Succeeded after 10.2s with 189 outputs (193 actions)

查看Person.g.dart

// GENERATED CODE - DO NOT MODIFY BY HANDpart of 'Person.dart';// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************Person _$PersonFromJson(Map<String, dynamic> json) => Person(json['id'] as int,json['name'] as String,json['email'] as String,(json['phone_numbers'] as List<dynamic>).map((e) => PhoneNumber.fromJson(e as Map<String, dynamic>)).toList(),);Map<String, dynamic> _$PersonToJson(Person instance) => <String, dynamic>{'id': instance.id,'name': instance.name,'email': instance.email,'phone_numbers': instance.phoneNumbers,};PhoneNumber _$PhoneNumberFromJson(Map<String, dynamic> json) => PhoneNumber(json['type'] as String,json['number'] as String,);Map<String, dynamic> _$PhoneNumberToJson(PhoneNumber instance) =><String, dynamic>{'type': instance.type,'number': instance.number,};

使用示例：

void jsonTest() {final json = '''
{"id": 1,"name": "John","email": "john@example.com","phone_numbers": [{"type": "home","number": "1234567890"},{"type": "work","number": "0987654321"}]
}
''';final person = Person.fromJson(jsonDecode(json));print("steve:${person.name}");final jsonEncoded = jsonEncode(person.toJson());print("steve:$jsonEncoded");}

打印的日志：

I/flutter ( 1781): steve:John
I/flutter ( 1781): steve:{"id":1,"name":"John","email":"john@example.com","phone_numbers":[{"type":"home","number":"1234567890"},{"type":"work","number":"0987654321"}]}

补充：

jsonKey

• nullable：默认为true，表示该字段可为null。
• defaultValue：如果源JSON不包含该key或该key的value为null，提供一个默认值。
• name：别名，若为null则默认为字段名。
• required：默认为false，若为真会检查JSON是否包含该key，若没有则抛出异常(key为null也是有效的)。

生成.g.dart文件

一次性构建

flutter packages pub run build_runner build

删除后重新构建

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

自动为后续创建的数据模型创建

flutter packages pub run build_runner watch