动态键值的json解析中的颤振问题答案

【问题标题】：flutter problem in json parsing of dynamic key values动态键值的json解析中的颤振问题
【发布时间】：2020-11-22 07:56:06
【问题描述】：

以下是我的 JSON 的输出

{
    "success": true,
    "data": {
        "ones": [{
                "id": "2",
                "username": "LM10002"
            },
            {
                "id": "6",
                "username": "LM10006"
            }
        ],
        "twos": [{
                "id": "3",
                "username": "LM10003"
            },
            {
                "id": "8",
                "username": "LM10008"
            }
        ],
        "threes": [{
            "id": "4",
            "username": "LM10004"
        }],
        "fours": [{
                "id": "5",
                "username": "LM10005"
            },
            {
                "id": "14",
                "username": "GT10014"
            }
        ]
    }
}

这里的键 ones, twos, threes, fours 是动态键值我尝试解析并能够获取的值

  DownLineModel({this.success, this.data});
  DownLineModel.fromJson(Map<String, dynamic> json) {
    success = json['success'];
    data = json['data'];
    print(data);

如何解析 json 并找到关键术语并再次解析它。

【问题讨论】：

标签： json flutter dart

【解决方案1】：

只需查看我根据您提供的 json 为您制作的示例即可。

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:json_parsing_example/models.dart';
import 'package:http/http.dart' as http;

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: HomePage());
  }
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  double value;

  String json = '''
  {
    "success": true,
    "data": {
        "ones": [{
                "id": "2",
                "username": "LM10002"
            },
            {
                "id": "6",
                "username": "LM10006"
            }
        ],
        "twos": [{
                "id": "3",
                "username": "LM10003"
            },
            {
                "id": "8",
                "username": "LM10008"
            }
        ],
        "threes": [{
            "id": "4",
            "username": "LM10004"
        }],
        "fours": [{
                "id": "5",
                "username": "LM10005"
            },
            {
                "id": "14",
                "username": "GT10014"
            }
        ]
    }
}
  
  ''';
  @override
  void initState() {
    super.initState();

    getData();
  }

  getData() {
    Map mapValue = jsonDecode(json);
    // This is where you iterate via the data object
    // that is the value which is key,value pair
    List<Data> data = List();
    mapValue['data'].forEach((key, value) {
      List<User> user = List();
      value.forEach((item) {
        user.add(User(id: item['id'], username: item['username']));
      });
      data.add(Data(name: key, userList: user));
    });

    data.forEach((element) {
      print(element.name + " : " + '${element.userList.length}');
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(child: Text('s')),
    );
  }
}

class Data {
  final String name;
  final List<User> userList;

  Data({this.name, this.userList});
}

class User {
  final String id;
  final String username;

  User({this.id, this.username});
}

让我知道它是否有效。

【讨论】：

【解决方案2】：

除非this.data 是Map<dynamic, dynamic>，否则您的代码将无法工作。您必须使用自己的 DataModel.fromJson(Map json) 方法为 data 属性创建一个单独的类。然后在 DownLineModel 构造函数中，您可以像这样简单地解析数据 json：

this.data = DataModel.fromJson(jsonData);

【讨论】：

【解决方案3】：

json['data'] 将是 Map<String, dynamic>。因此，您可以使用 forEach 迭代这些动态键。

json['data'].forEach((dynamicKey, list) {
  // dynamicKey will be 'ones', 'twos', ....
  // list will be the corresponding list of maps
});

【讨论】：

【解决方案4】：

假设当你这样做print(data)，你得到这个响应

    {
        "ones": [{
                "id": "2",
                "username": "LM10002"
            },
            {
                "id": "6",
                "username": "LM10006"
            }
        ],
        "twos": [{
                "id": "3",
                "username": "LM10003"
            },
            {
                "id": "8",
                "username": "LM10008"
            }
        ],
        "threes": [{
            "id": "4",
            "username": "LM10004"
        }],
        "fours": [{
                "id": "5",
                "username": "LM10005"
            },
            {
                "id": "14",
                "username": "GT10014"
            }
        ]
    }

现在，我们可以做的是，再次遍历数据，并找到dynamic keys，如ones、twos....

我们可以做这样的事情。我只为ones 向您展示，您可以为资源做这些

//for ones
List<Map<String, String>> ones = data["ones"];

//iterating over it
ones.forEach((element){
   // we are now inside the array
   // iterating over element which is {"id": "", "username": ""}
   element.forEach((key, value){
      print("$key => $value");
   });
});

// OUTPUT
// id => 2
// username => LM10002
// id => 6
// username => LM10006

【讨论】：