如何获取 json 数据并根据参数将其分离？

Question

我这里有一个 json 对象 -

{
    "error": "0",
    "message": "Got it!",
    "data": [
        {
            "status": false,
            "_id": "5e2fbb74d465702288c54038",
            "group_id": "5e0d9e993944e46ed9a86d95",
            "date": "2020-01-28T00:00:00.000Z",
            "title": "cciigcigc",
            "priority": 3,
            "description": "",
            "tasks": [],
            "created_date": "2020-01-28T04:41:24.576Z",
            "__v": 0
        }
    ]
}

我想根据 ["data"]["status"] 参数获取它；如果状态为假，则返回一个单独的列表，如果状态为真，则返回另一个列表。我试图以这种方式修改我当前的 fetch 方法 -

Future<List<Post>> gettask(bool identifier) async { // the identifier can be set to true and false 
  List<Post> statusComplete;
  List<Post> statusInComplete;

  String link = baseURL + fetchTodoByDate;
//  print("printing from get task = $setter");
  Stopwatch stopwatchbefore = new Stopwatch()..start();


  var res = await http.post(Uri.encodeFull(link), headers: {"Accept": "application/json", }, body: {"date" : setter.toString()});

  print('fetch executed in ${stopwatchbefore.elapsed}');


  if (res.statusCode == 200) {
    Stopwatch stopwatchafter = new Stopwatch()
      ..start();

    var data = json.decode(res.body);
    var rest = data["data"] as List;
    if(identifier == true){
      statusComplete = rest.map<Post>((json) {
        // need help in implementing logic here

        return Post.fromJson(json);
      }).toList();

      return statusComplete;

    }else if(identifier == false){
      statusInComplete = rest.map<Post>((json) {
        // need help in implementing logic here

        return Post.fromJson(json);
      }).toList();
      return statusInComplete;
    }

    print('statuscode executed in ${stopwatchafter.elapsed}');
    Future.delayed(Duration(seconds: 5));
  }


//  print("List Size: ${list.length}");
}

这是我第一次尝试以这种方式获取和分离数据。我试图看一些教程，但似乎没有一个能满足我的情况。

我能得到一些关于如何获取数据然后根据参数将其分开的建议吗？

Answer 1

查看下面的示例，它将给出流程如何工作的基本概念。

import 'package:flutter/material.dart';
import 'dart:async';
import 'package:flutter/services.dart';
import 'package:json_parsing/models.dart';

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  List<Datum> dataList = List();
  bool _isLoading = false;


  Future<String> loadFromAssets() async {
    return await rootBundle.loadString('json/parse.json');
  }

  Future loadyourData() async {
    setState(() {
      _isLoading = true;
    });

// this is the local json that i have loaded from the assets folder
// you can make the http call here and else everything later is the same.

    String jsonString = await loadFromAssets();
    final yourData = dataFromJson(jsonString);

    dataList = yourData.data;

  var statusComplete = dataList.where((i) => i.status == true).toList();

    for (int i = 0; i < statusComplete.length; i++) {
      print('This is the list for true status :${statusComplete[i].title}');
    }

    var statusInComplete = dataList.where((i) => i.status == false).toList();
    print(statusInComplete[0].title);




    setState(() {
      _isLoading = false;
    });
  }

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

    loadyourData();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
          body: Container(
        child: _isLoading
            ? CircularProgressIndicator()
            : new ListView.builder(
                itemCount: dataList.length,
                itemBuilder: (BuildContext ctxt, int index) {
                  return new Text(dataList[index].status.toString());
                }),
      )),
    );
  }
}

下面是模型类

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

import 'dart:convert';

Data dataFromJson(String str) => Data.fromJson(json.decode(str));

String dataToJson(Data data) => json.encode(data.toJson());

class Data {
    String error;
    String message;
    List<Datum> data;

    Data({
        this.error,
        this.message,
        this.data,
    });

    factory Data.fromJson(Map<String, dynamic> json) => Data(
        error: json["error"],
        message: json["message"],
        data: List<Datum>.from(json["data"].map((x) => Datum.fromJson(x))),
    );

    Map<String, dynamic> toJson() => {
        "error": error,
        "message": message,
        "data": List<dynamic>.from(data.map((x) => x.toJson())),
    };
}

class Datum {
    bool status;
    String id;
    String groupId;
    DateTime date;
    String title;
    int priority;
    String description;
    List<dynamic> tasks;
    DateTime createdDate;
    int v;

    Datum({
        this.status,
        this.id,
        this.groupId,
        this.date,
        this.title,
        this.priority,
        this.description,
        this.tasks,
        this.createdDate,
        this.v,
    });

    factory Datum.fromJson(Map<String, dynamic> json) => Datum(
        status: json["status"],
        id: json["_id"],
        groupId: json["group_id"],
        date: DateTime.parse(json["date"]),
        title: json["title"],
        priority: json["priority"],
        description: json["description"],
        tasks: List<dynamic>.from(json["tasks"].map((x) => x)),
        createdDate: DateTime.parse(json["created_date"]),
        v: json["__v"],
    );

    Map<String, dynamic> toJson() => {
        "status": status,
        "_id": id,
        "group_id": groupId,
        "date": date.toIso8601String(),
        "title": title,
        "priority": priority,
        "description": description,
        "tasks": List<dynamic>.from(tasks.map((x) => x)),
        "created_date": createdDate.toIso8601String(),
        "__v": v,
    };
}

这是你指定的 json

{
    "error": "0",
    "message": "Got it!",
    "data": [
        {
            "status": false,
            "_id": "5e2fbb74d465702288c54038",
            "group_id": "5e0d9e993944e46ed9a86d95",
            "date": "2020-01-28T00:00:00.000Z",
            "title": "first",
            "priority": 3,
            "description": "",
            "tasks": [],
            "created_date": "2020-01-28T04:41:24.576Z",
            "__v": 0
        },
        {
            "status": true,
            "_id": "5e2fbb74d465702288c54038",
            "group_id": "5e0d9e993944e46ed9a86d95",
            "date": "2020-01-28T00:00:00.000Z",
            "title": "second",
            "priority": 3,
            "description": "",
            "tasks": [],
            "created_date": "2020-01-28T04:41:24.576Z",
            "__v": 0
        },
        {
            "status": true,
            "_id": "5e2fbb74d465702288c54038",
            "group_id": "5e0d9e993944e46ed9a86d95",
            "date": "2020-01-28T00:00:00.000Z",
            "title": "third",
            "priority": 3,
            "description": "",
            "tasks": [],
            "created_date": "2020-01-28T04:41:24.576Z",
            "__v": 0
        }
    ]
}

Answer 2

试试这个模型类

import 'dart:convert';

Jsonmodel jsonmodelFromJson(String str) => Jsonmodel.fromJson(json.decode(str));

String jsonmodelToJson(Jsonmodel data) => json.encode(data.toJson());

class Jsonmodel {
    String error;
    String message;
    List<Datum> data;

    Jsonmodel({
        this.error,
        this.message,
        this.data,
    });

    factory Jsonmodel.fromJson(Map<String, dynamic> json) => Jsonmodel(
        error: json["error"],
        message: json["message"],
        data: List<Datum>.from(json["data"].map((x) => Datum.fromJson(x))),
    );

    Map<String, dynamic> toJson() => {
        "error": error,
        "message": message,
        "data": List<dynamic>.from(data.map((x) => x.toJson())),
    };
}

class Datum {
    bool status;
    String id;
    String groupId;
    DateTime date;
    String title;
    int priority;
    String description;
    List<dynamic> tasks;
    DateTime createdDate;
    int v;

    Datum({
        this.status,
        this.id,
        this.groupId,
        this.date,
        this.title,
        this.priority,
        this.description,
        this.tasks,
        this.createdDate,
        this.v,
    });

    factory Datum.fromJson(Map<String, dynamic> json) => Datum(
        status: json["status"],
        id: json["_id"],
        groupId: json["group_id"],
        date: DateTime.parse(json["date"]),
        title: json["title"],
        priority: json["priority"],
        description: json["description"],
        tasks: List<dynamic>.from(json["tasks"].map((x) => x)),
        createdDate: DateTime.parse(json["created_date"]),
        v: json["__v"],
    );

    Map<String, dynamic> toJson() => {
        "status": status,
        "_id": id,
        "group_id": groupId,
        "date": date.toIso8601String(),
        "title": title,
        "priority": priority,
        "description": description,
        "tasks": List<dynamic>.from(tasks.map((x) => x)),
        "created_date": createdDate.toIso8601String(),
        "__v": v,
    };
}

这样使用

var res = await http.post(Uri.encodeFull(link), headers: {"Accept": 
 "application/json", }, body: {"date" : setter.toString()});

    Jsonmodel modeldata = jsonmodelFromJson(res);
    // do your stuff
    modeldata.data.foreach((data){
        if(data.status){
          //do your stuff
        }else{
          //do your stuff
        }
    });