Dart/Flutter: Parsing Json object

You can use json2dart to convert your json to dart classes even complex and nested json datas will work perfectly.

Here is dart class version of your given json data:

class Autogenerated {
  NewDataSet newDataSet;

  Autogenerated({this.newDataSet});

  Autogenerated.fromJson(Map<String, dynamic> json) {
    newDataSet = json['NewDataSet'] != null
        ? new NewDataSet.fromJson(json['NewDataSet'])
        : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.newDataSet != null) {
      data['NewDataSet'] = this.newDataSet.toJson();
    }
    return data;
  }
}

class NewDataSet {
  List<Route> route;

  NewDataSet({this.route});

  NewDataSet.fromJson(Map<String, dynamic> json) {
    if (json['Route'] != null) {
      route = new List<Route>();
      json['Route'].forEach((v) {
        route.add(new Route.fromJson(v));
      });
    }
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.route != null) {
      data['Route'] = this.route.map((v) => v.toJson()).toList();
    }
    return data;
  }
}

class Route {
  String routeID;
  String routeNum;
  String description;

  Route({this.routeID, this.routeNum, this.description});

  Route.fromJson(Map<String, dynamic> json) {
    routeID = json['RouteID'];
    routeNum = json['RouteNum'];
    description = json['Description'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['RouteID'] = this.routeID;
    data['RouteNum'] = this.routeNum;
    data['Description'] = this.description;
    return data;
  }
}

You can chain the square brackets and simply refer to the respective names, as long as you know the data you're receiving.

import 'dart:convert';

void main() {
  decodeJSON();
}

void decodeJSON() async {
  String data =
        '{"NewDataSet": {"Route": [{"RouteID": "1","RouteNum": "20","Description": "NORTH DAKOTA "},{"RouteID": "11","RouteNum": "25","Description": "East SD "}]}}';

    try {
      dynamic decoded = await jsonDecode(data);
      dynamic newDataSet = await decoded['NewDataSet'];
      dynamic routes = await decoded['NewDataSet']['Route'];

      print(newDataSet);
      print(routes);
    } catch (e) {
      print(e);
    }
}