Flutter 中 JSON 解析

使用 json_serializable, build_runner, json_annotation 解決 JSON -> Model 的問題。

設置依賴

dependencies:
  json_annotation: ^1.1.0

dev_dependencies:
  build_runner: ^0.10.2
  json_serializable: ^1.2.0

創建一個 Model

model/user_model.dart

import 'package:json_annotation/json_annotation.dart';

part 'user_model.g.dart';

@JsonSerializable()
class UserModel {
  String name;
  int age;

  UserModel(this.name, this.age);

  factory UserModel.fromJson(Map<String, dynamic> json) =>
      _$UserModelFromJson(json);

  Map<String, dynamic> toJson() => _$UserModelToJson(this);
}

寫完後會報錯，先不管

使用 build_runner 自動生成 JSON解析 相關的代碼

創建 JSON 解析文件：在工程目錄下執行下面命令

flutter packages pub run build_runner build

執行完成後，在 model 文件夾下會生成 user_model.g.dart 文件, user_model.dart 的報錯會消失。

寫個單元測試

在 test 文件夾下：

json_test.dart

import 'package:flutter_test/flutter_test.dart';
import 'dart:convert';

import 'package:flutter_app/model/user_model.dart';

void main() {
  String JSON_STRING = '''{"name":"fangmingdong","age":12}''';

  group('jsonparse test', () {

    test('to json', () {
      UserModel userModel = UserModel('fangmingdong', 12);
      String jsonStr = json.encode(userModel.toJson());
      print(jsonStr);
      expect(jsonStr, JSON_STRING);
    });

    test('mockdata test', () {
      UserModel userModel = UserModel.fromJson(json.decode(JSON_STRING));
      expect(userModel.age, 12);
      expect(userModel.name, 'fangmingdong');
    });
    
  });
}

工程級封裝

通常接口設計都是以下面格式的：

{
  "code": 200,
  "msg": "success",
  "data":{
      ...
  }
}

Android 中通常使用泛型解析上面的 JSON:

public class BaseResponse<T>{
  int code;
  String msg;
  T data;
}

但是 json_serializable 並不支持泛型解析。

不太優雅的解決方案 繼承

解析：

{
  "code": 200,
  "msg": "success",
  "data": {
    "name": "fangmingdong",
    "age": 12,
    "book": {
      "id": 1,
      "name": "從你的全世界路過"
    }
  }
}

base_response.dart:

import 'package:json_annotation/json_annotation.dart';

part 'base_response.g.dart';

@JsonSerializable()
class BaseResponse{

  int code;
  String msg;

  BaseResponse(this.code, this.msg);

  factory BaseResponse.fromJson(Map<String, dynamic> json) =>
      _$BaseResponseFromJson(json);

  Map<String, dynamic> toJson() => _$BaseResponseToJson(this);

}

user_model.dart:

import 'package:flutter_app/model/base_response.dart';
import 'package:flutter_app/model/book_model.dart';
import 'package:json_annotation/json_annotation.dart';

part 'user_model.g.dart';

@JsonSerializable()
class UserModel extends BaseResponse {
  UserModelReal data;

  UserModel(this.data) : super(0, '');

  factory UserModel.fromJson(Map<String, dynamic> json) =>
      _$UserModelFromJson(json);

  Map<String, dynamic> toJson() => _$UserModelToJson(this);
}

@JsonSerializable()
class UserModelReal {
  String name;
  int age;
  BookModel book;

  UserModelReal(this.name, this.age, this.book);

  factory UserModelReal.fromJson(Map<String, dynamic> json) =>
      _$UserModelRealFromJson(json);

  Map<String, dynamic> toJson() => _$UserModelRealToJson(this);
}

test:

import 'package:flutter_test/flutter_test.dart';
import 'dart:convert';

import 'package:flutter_app/model/user_model.dart';
import 'package:flutter_app/model/book_model.dart';

void main() {
  String JSON_STRING = '''{"code":200,"msg":"success","data":{"name":"fangmingdong","age":12,"book":{"id":1,"name":"從你的全世界路過"}}}''';

  group('jsonparse test', () {

    test('to json', () {
      UserModel userModel = UserModel(new UserModelReal('fangmingdong', 12, BookModel(1, '從你的全世界路過')));
      String jsonStr = json.encode(userModel.toJson());
      print(jsonStr);
//      expect(jsonStr, JSON_STRING);
    });

    test('mockdata test', () {
      UserModel userModel = UserModel.fromJson(json.decode(JSON_STRING));
      expect(userModel.data.age, 12);
      expect(userModel.data.name, 'fangmingdong');
      expect(userModel.code, 200);
      expect(userModel.msg, "success");
    });
    
  });
}

參考：

• https://juejin.im/post/5b5f00e7e51d45190571172f