Flutter : How to parse JSON Array of Array of objects

Question

Can anyone tell me how to parse arrays of arrays of object in flutter. When I am parsing the json I am getting error as List<dynamic> is not a subtype of type Map<String, dynamic>.

I have used quicktype to write the model class and I am trying to print the worksheetData in the Future but I am getting error. Below is my json file which needs to be parsed. Please help me to fix this issue. Stuck since two days.

[
    {
        "_id": "5ebae61440315c41995eccc7",
        "projectName": "NSM",
        "sheetName": "Priliminaries - A1",
        "worksheetData": [
            [
                {
                    "serial": "Sl.No",
                    "description": "ITEM DESCRIPTION",
                    "quantity": "QTY.",
                    "unit": "UNIT",
                    "unitrate": "UNIT PRICE",
                }
            ],
            null,
            [
                {
                    "serial": "1.1",
                    "description": "Allowance for CAR policy, Mobilization, demobilization after works, Firstaid boxes, Fire extinguishers etc.",
                    "quantity": 1,
                    "unit": "Lot",
                    "unitrate": 12500,
                }
            ],
            [
                {
                    "serial": "1.2",
                    "description": "Demolition of existing gypsum partitions, ceilings, necessary floor tiles etc and cart away debris if any",
                    "quantity": 0,
                    "unit": "Lot",
                    "unitrate": 5000,
                }
            ]
        ],
        "__v": "0"
    },
    {
        "_id": "5ebae61440315c41995eccc8",
        "projectName": "NSM",
        "sheetName": "General works -A2",
        "worksheetData": [
            [
                {
                    "serial": "Sl.No",
                    "description": "ITEM DESCRIPTION",
                    "quantity": "QTY.",
                    "unit": "UNIT",
                    "unitrate": "UNIT PRICE",
                }
            ],
            null,
            [
                {
                    "serial": "1.1",
                    "description": "Allowance for CAR policy, Mobilization, demobilization after works, Firstaid boxes, Fire extinguishers etc.",
                    "quantity": 1,
                    "unit": "Lot",
                    "unitrate": 12500,
                }
            ],
            [
                {
                    "serial": "1.2",
                    "description": "Demolition of existing gypsum partitions, ceilings, necessary floor tiles etc and cart away debris if any",
                    "quantity": 0,
                    "unit": "Lot",
                    "unitrate": 5000,
                }
            ]
        ],
        "__v": "0"
    }
]

Main.dart

class WorkSheet extends StatefulWidget {
  const WorkSheet({Key key}) : super(key: key);
  @override
  _WorkSheetState createState() => new _WorkSheetState();
}

class _WorkSheetState extends State<WorkSheet> {
  // List<ArticleslistData> articleslist = [];
  // List<ArticleslistData> list;

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

  Future loadSheetDataFromAssets() async {
    var jsonData = await rootBundle.loadString('assets/Vibyor.json');
    var data = json.decode(jsonData);
    ArticleslistData articleslistData = new ArticleslistData.fromJson(data);
     print('data : ${articleslistData.worksheetData[0]}');
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Work sheet data'),
      ),
      body: FutureBuilder(
          future: loadSheetDataFromAssets(),
          builder: (context, snapshot) {
            return snapshot.data != null
                ? Text(snapshot.data)
                : Center(child: CircularProgressIndicator());
          }),
    );
  }
}

please add class ArticlesListData to Your question, since I don't know what fields it has. — num8er
– num8er, Commented Jun 5, 2020 at 16:54

num8er · Accepted Answer · 2020-06-05 18:14:55Z

1

I've refactored Your classes:

class ArticleslistData {
  String sId;
  String projectName;
  String sheetName;
  List<WorksheetData> worksheetData = [];
  String sV;

  ArticleslistData(this.sId, this.projectName, this.sheetName, this.worksheetData, this.sV);

  static ArticleslistData fromMap(Map<String, dynamic> map) {
    List<WorksheetData> worksheetData = [];
    if (map['worksheetData'] != null) {
      for (Iterable row in map['worksheetData']) {
        if (row == null) continue;
        for (Map map in row) {
          worksheetData.add(WorksheetData.fromMap(map));
        }
      }
    }

    return ArticleslistData(
      map['_id'],
      map['projectName'],
      map['sheetName'],
      worksheetData,
      map['__v']
    );
  }

  Map<String, dynamic> toMap() {
    return {
      "_id":            this.sId,
      "projectName":    this.projectName,
      "sheetName":      this.sheetName,
      "worksheetData":  this.worksheetData,
      "__v":            this.sV
    };
  }
}

class WorksheetData {
  String serial;
  String description;
  String quantity;
  String unit;
  String unitrate;

  WorksheetData(this.serial, this.description, this.quantity, this.unit, this.unitrate);

  static WorksheetData fromMap(Map map) {
    return WorksheetData(
        map['serial'].toString(),
        map['description'].toString(),
        map['quantity'].toString(),
        map['unit'].toString(),
        map['unitrate'].toString()
    );
  }

  Map<String, dynamic> toMap() {
    return {
      "serial":       this.serial,
      "description":  this.description,
      "quantity":     this.quantity,
      "unit":         this.unit,
      "unitrate":     this.unitrate
    };
  }
}

Usage:

Future loadSheetDataFromAssets() async {
  var jsonData = await rootBundle.loadString('assets/Vibyor.json');
  var data = json.decode(jsonData);

  this.articleslist = [];
  List<ArticleslistData> items = [];
  data.forEach((item) {
    items.add(ArticleslistData.fromMap(element));
  });
  this.articleslist = items;

  print('data : ${this.articleslist[0].worksheetData[0]}');
  return this.articleslist;
}

Don't forget to uncomment following from Your _WorkSheetState widget:

List<ArticleslistData> articleslist = [];

P.S. fromJson and toJson method names are not valid, so I renamed them to fromMap, toMap since You were working maps. JSON is string that You decoded, after decode it becomes Iterable and Map.

Small hint: if You want to easily solve Your issues - use IntelliJ Idea Community Edition and do debug by setting breakpoints.

edited Jun 5, 2020 at 18:14

answered Jun 5, 2020 at 18:02

num8er

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4 Comments

Mahant Over a year ago

this throws me an error _TypeError (type 'String' is not a subtype of type 'Iterable<dynamic>') in model class

num8er Over a year ago

print(data); what You see?

num8er Over a year ago

import 'dart:convert'; at top of file and use: jsonDecode(jsonData) instead of json.decode

Mahant Over a year ago

still the same issue

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