Flutter中Json解析

json.decode

json.decode返回值为Map<String, dynamic>直到运行的时候才能知道具体的类型

所以不能：类型检查，自动提示，编译时无法发现错误

json_serializable

（1）pubspec.yaml中添加依赖

dependencies:
  json_annotation: ^2.0.0  # https://pub.dartlang.org/packages/json_annotation

dev_dependencies:
  build_runner: ^1.1.2  # https://pub.dartlang.org/packages/build_runner
  json_serializable: ^2.0.1  # https://pub.dartlang.org/packages/json_serializable

（2）创建Model并添加注解

import 'package:json_annotation/json_annotation.dart';

part 'person.g.dart';

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

  Person(this.name, this.age);

  factory Person.fromJson(Map<String, dynamic> json) => _$PersonFromJson(json);
  Map<String, dynamic> toJson() => _$PersonToJson(this);
}

（3）自动生成fromJson和toJson（model.g.dart）

flutter packages pub run build_runner build

代码示例

import 'package:flutter/material.dart';
import 'dart:convert';

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

class JsonDemoPage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => new _JsonDemoPagePageState();
}

class _JsonDemoPagePageState extends State<JsonDemoPage> {
  String name = "test";
  User user = null;
  Person person = null;

  @override
  void initState() {
    super.initState();
  }

  @override
  void didUpdateWidget(covariant JsonDemoPage oldWidget) {
    name = JsonDecoder.parseJson2Map();
    user = JsonDecoder.parseJson2Object();
    person = JsonDecoder.parseJsonSerialize();
  }

  Widget build(BuildContext context) {
    return Scaffold(
        appBar: new AppBar(
          title: new Text('JSON Demo'),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text('name: $name'),
              SizedBox(height: 10,),
              Text('User: [name: ${user.name}, homepage: ${user.homepage}]', textAlign: TextAlign.center,),
              SizedBox(height: 10,),
              Text('Person: ${person.toJson()}', textAlign: TextAlign.center,),
            ],
          )
        ),
    );
  }
}

class JsonDecoder {

  //json.decode返回值为Map<String, dynamic>直到运行的时候才能知道具体的类型
  //所以不能：类型检查，自动提示，编译时无法发现错误，严重不推荐！
  static String parseJson2Map() {
    String jsonStr = '{"name": "Joe.Ye"}';
    var user = json.decode(jsonStr);
    print('${user['name']}');
    return '${user['name']}';
  }

  //手写fromJson, toJson不太友好
  static User parseJson2Object() {
    String jsonStr = '{"name":"Joe.Ye", "email": "yezhou@yezhou.org", "homepage":"http://www.appblog.cn"}';
    Map userMap = json.decode(jsonStr);
    var user = new User.fromJson(userMap);
    print('${user.name}');
    print(user.toJson());
    return user;
  }

  static Person parseJsonSerialize() {
    String jsonStr = '{"name":"Joe.Ye", "age":30}';
    Map personMap = json.decode(jsonStr);
    return Person.fromJson(personMap);
  }

  //https://javiercbk.github.io/json_to_dart/
}

class User {
  final String name;
  final String email;
  final String homepage;

  User(this.name, this.email, this.homepage);

  User.fromJson(Map<String, dynamic> json)
      : name = json['name'],
        email = json['email'],
        homepage = json['homepage'];

  Map<String, dynamic> toJson() => {
    'name': name,
    'email': email,
    'homepage': homepage
  };
}