json - 如何在 Flutter 中映射具有相同类型嵌套对象的 json？

Question

我需要在 Flutter 中映射这个 json，我尝试使用 fromMap of JsonCodec 但抛出 StackOverflowError。任何建议将非常受欢迎。

{
"items": [
    {
        "id": 59,
        "name": "Trastornos de la glándula tiroides",
        "parent": {
            "id": 58,
            "name": "Enfermedades endócrinas",
            "parent": null,
            "diagnosis_classifications": {
                "count": 1,
                "items": [
                    {
                        "id": 58,
                        "name": "CIE-10 Diagnósticos",
                        "code": "E00-E35"
                    }
                ]
            }
        },
        "diagnosis_classifications": {
            "count": 1,
            "items": [
                {
                    "id": 59,
                    "name": "CIE-10 Diagnósticos",
                    "code": "E00-E07"
                }
            ]
        }
    }
]

}

Answer 1

你可以用 var payload = payloadFromJson(jsonString); 削
您可以在完整代码中看到很长的示例 json 字符串
相关类

// To parse this JSON data, do
//
//     final payload = payloadFromJson(jsonString);

import 'dart:convert';

Payload payloadFromJson(String str) => Payload.fromJson(json.decode(str));

String payloadToJson(Payload data) => json.encode(data.toJson());

class Parent {
    int id;
    String name;
    Payload parent;
    DiagnosisClassifications diagnosisClassifications;

    Parent({
        this.id,
        this.name,
        this.parent,
        this.diagnosisClassifications,
    });

    factory Parent.fromJson(Map<String, dynamic> json) => Parent(
        id: json["id"] == null ? null : json["id"],
        name: json["name"] == null ? null : json["name"],
        parent: json["parent"] == null ? null : Payload.fromJson(json["parent"]),
        diagnosisClassifications: json["diagnosis_classifications"] == null ? null : DiagnosisClassifications.fromJson(json["diagnosis_classifications"]),
    );

    Map<String, dynamic> toJson() => {
        "id": id == null ? null : id,
        "name": name == null ? null : name,
        "parent": parent == null ? null : parent.toJson(),
        "diagnosis_classifications": diagnosisClassifications == null ? null : diagnosisClassifications.toJson(),
    };
}

class Payload {
    int id;
    String name;
    Parent parent;
    DiagnosisClassifications diagnosisClassifications;

    Payload({
        this.id,
        this.name,
        this.parent,
        this.diagnosisClassifications,
    });

    factory Payload.fromJson(Map<String, dynamic> json) => Payload(
        id: json["id"] == null ? null : json["id"],
        name: json["name"] == null ? null : json["name"],
        parent: json["parent"] == null ? null : Parent.fromJson(json["parent"]),
        diagnosisClassifications: json["diagnosis_classifications"] == null ? null : DiagnosisClassifications.fromJson(json["diagnosis_classifications"]),
    );

    Map<String, dynamic> toJson() => {
        "id": id == null ? null : id,
        "name": name == null ? null : name,
        "parent": parent == null ? null : parent.toJson(),
        "diagnosis_classifications": diagnosisClassifications == null ? null : diagnosisClassifications.toJson(),
    };
}

class DiagnosisClassifications {
    int count;
    List<Item> items;

    DiagnosisClassifications({
        this.count,
        this.items,
    });

    factory DiagnosisClassifications.fromJson(Map<String, dynamic> json) => DiagnosisClassifications(
        count: json["count"] == null ? null : json["count"],
        items: json["items"] == null ? null : List<Item>.from(json["items"].map((x) => Item.fromJson(x))),
    );

    Map<String, dynamic> toJson() => {
        "count": count == null ? null : count,
        "items": items == null ? null : List<dynamic>.from(items.map((x) => x.toJson())),
    };
}

class Item {
    int id;
    String name;
    String code;

    Item({
        this.id,
        this.name,
        this.code,
    });

    factory Item.fromJson(Map<String, dynamic> json) => Item(
        id: json["id"] == null ? null : json["id"],
        name: json["name"] == null ? null : json["name"],
        code: json["code"] == null ? null : json["code"],
    );

    Map<String, dynamic> toJson() => {
        "id": id == null ? null : id,
        "name": name == null ? null : name,
        "code": code == null ? null : code,
    };
}

完整代码

import 'package:flutter/material.dart';
// To parse this JSON data, do
//
//     final payload = payloadFromJson(jsonString);

import 'dart:convert';

Payload payloadFromJson(String str) => Payload.fromJson(json.decode(str));

String payloadToJson(Payload data) => json.encode(data.toJson());

class Parent {
  int id;
  String name;
  Payload parent;
  DiagnosisClassifications diagnosisClassifications;

  Parent({
    this.id,
    this.name,
    this.parent,
    this.diagnosisClassifications,
  });

  factory Parent.fromJson(Map<String, dynamic> json) => Parent(
    id: json["id"] == null ? null : json["id"],
    name: json["name"] == null ? null : json["name"],
    parent: json["parent"] == null ? null : Payload.fromJson(json["parent"]),
    diagnosisClassifications: json["diagnosis_classifications"] == null ? null : DiagnosisClassifications.fromJson(json["diagnosis_classifications"]),
  );

  Map<String, dynamic> toJson() => {
    "id": id == null ? null : id,
    "name": name == null ? null : name,
    "parent": parent == null ? null : parent.toJson(),
    "diagnosis_classifications": diagnosisClassifications == null ? null : diagnosisClassifications.toJson(),
  };
}

class Payload {
  int id;
  String name;
  Parent parent;
  DiagnosisClassifications diagnosisClassifications;

  Payload({
    this.id,
    this.name,
    this.parent,
    this.diagnosisClassifications,
  });

  factory Payload.fromJson(Map<String, dynamic> json) => Payload(
    id: json["id"] == null ? null : json["id"],
    name: json["name"] == null ? null : json["name"],
    parent: json["parent"] == null ? null : Parent.fromJson(json["parent"]),
    diagnosisClassifications: json["diagnosis_classifications"] == null ? null : DiagnosisClassifications.fromJson(json["diagnosis_classifications"]),
  );

  Map<String, dynamic> toJson() => {
    "id": id == null ? null : id,
    "name": name == null ? null : name,
    "parent": parent == null ? null : parent.toJson(),
    "diagnosis_classifications": diagnosisClassifications == null ? null : diagnosisClassifications.toJson(),
  };
}

class DiagnosisClassifications {
  int count;
  List<Item> items;

  DiagnosisClassifications({
    this.count,
    this.items,
  });

  factory DiagnosisClassifications.fromJson(Map<String, dynamic> json) => DiagnosisClassifications(
    count: json["count"] == null ? null : json["count"],
    items: json["items"] == null ? null : List<Item>.from(json["items"].map((x) => Item.fromJson(x))),
  );

  Map<String, dynamic> toJson() => {
    "count": count == null ? null : count,
    "items": items == null ? null : List<dynamic>.from(items.map((x) => x.toJson())),
  };
}

class Item {
  int id;
  String name;
  String code;

  Item({
    this.id,
    this.name,
    this.code,
  });

  factory Item.fromJson(Map<String, dynamic> json) => Item(
    id: json["id"] == null ? null : json["id"],
    name: json["name"] == null ? null : json["name"],
    code: json["code"] == null ? null : json["code"],
  );

  Map<String, dynamic> toJson() => {
    "id": id == null ? null : id,
    "name": name == null ? null : name,
    "code": code == null ? null : code,
  };
}

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  String jsonStr = '''  {
        "id": 59,
        "name": "Trastornos de la glándula tiroides",
        "parent": {
            "id": 58,
            "name": "Enfermedades endócrinas",
            "parent" : {
            "id": 60,
            "name": "Enfermedades endócrinas",
            "parent" : null,
            "diagnosis_classifications": {
                "count": 1,
                "items": [
                    {
                        "id": 60,
                        "name": "CIE-10 Diagnósticos",
                        "code": "E00-E35"
                    }
                ]
            }
        },
            "diagnosis_classifications": {
                "count": 1,
                "items": [
                    {
                        "id": 58,
                        "name": "CIE-10 Diagnósticos",
                        "code": "E00-E35"
                    }
                ]
            }
        }

    }  ''';

  void _incrementCounter() {
    final payload = payloadFromJson(jsonStr);
    print('payload.id ${payload.id}');
    print('payload.parent.id ${payload.parent.id}');
    print('payload.parent.parent.id ${payload.parent.parent.id}');
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

输出

I/flutter ( 8924): payload.id 59
I/flutter ( 8924): payload.parent.id 58
I/flutter ( 8924): payload.parent.parent.id 60