Deserializar json vector in Dart/Flutter

Question

I’m trying to deserialize this json vector [{"i":737,"n":1}] but I’m not getting the variables "i" and "n".

Class to deserialize

class PortasAbertas {
  int i;
  int n;

  PortasAbertas({this.i, this.n});

  PortasAbertas.fromJson(Map<int, dynamic> json) {
    i = json[i];
    n = json[n];
  }

  Map<int, dynamic> toJson() {
    final Map<int, dynamic> data = new Map<int, dynamic>();
    data[i] = this.i;
    data[n] = this.n;
    return data;
  }
}

Object I’m using to deserialize

 if (endereco == "portasabertas") {
     PortasAbertas objeto = new PortasAbertas.fromJson(responseJson);
      if (objeto.n == "[]"){
        _msg = ("Nenhuma porta esta aberta");
      } else {
        _msg = ("Portas abertas ${objeto.n}");
      }
    }

Answer 1

Here’s an example of how you can do it

class Service extends Entity{
  int           id;
  int           idUser;
  DateTime      startDate;
  DateTime      endDate;
  String        title;
  String        subtitle;
  String        description;
  double        price;
  int           ranking;

  dynamic toClass(Map<String, dynamic>  data){
    id          = data["id"];
    idUser      = data["iduser"];
    startDate   = DateTime.parse(data["startdate"]);
    endDate     = (data["enddate"]=="null") ? DateTime.parse(data["enddate"]) : null;
    image       = data["image"];
    title       = data["title"];
    subtitle    = data["subtitle"];
    description = data["description"];
    price       = double.parse(data["price"]??0);
    ranking     = 0;

    return this;
  }

  Map<String, dynamic> toJSON(){

    return {
      // "id"          : "$id",
      "idUser"      : "$idUser",    
      "startDate"   : "$startDate",          
      "endDate"     : "$endDate",            
      "image"       : "$image",             
      "title"       : "$title",     
      "subtitle"    : "$subtitle",       
      "description" : "$description",       
      "price"       : "$price",             
      "ranking"     : ranking,
    };
  }  
}

Note: This is an excerpt from a class I use in my project

Explanation

JSON always returns a set of KEY : VALUE where the KEY is always a String, soon for you to fetch the data from a KEY you do as follows

variavel = json["CHAVE"];

This method of yours is somewhat wrong, because the parameter it receives does not match the JSON structure

  PortasAbertas.fromJson(Map<int, dynamic> json) {
    i = json[i];
    n = json[n];
  }

It is right for you to create the parameter as follows

Map<String, dynamic> json

That way it would be right

  PortasAbertas.fromJson(Map<String, dynamic> json) {
    i = json["i"];
    n = json["n"];
  }

Edited

I created this example, see if it fits you, because as you are receiving an array of objects, I believe you can receive data from more than one port...

import 'dart:convert';

/*Aqui é sua classe*/
class PortasAbertas {
  int i;
  int n;

  PortasAbertas({this.i, this.n});

  PortasAbertas fromJson(Map<String, dynamic> json) {
    this.i = json['i'];
    this.n = json['n'];
    return this;
  }

  Map<String, dynamic> toJson() {
    return {
      'i': i,
      'n': n
      };
  }
}

/*Aqui é como você irá utilizar a sua classe*/
void main() {
  var jsonData = '[{"i":737,"n":1}]';
  var parsedJson = json.decode(jsonData);
  
  dynamic portasAbertas = parsedJson.map((value){
    return value;
  }).toList();

  PortasAbertas objeto = PortasAbertas();
  objeto.fromJson(portasAbertas[0]);
  print('I = ${objeto.i}');
  print('N = ${objeto.n}');
}

Note: You can run this example here in this website and see how it works.

Explanation

I took your JSON, broke it into a list of Map<String, dynamic> who will own all of your Jsonarray’s objects. Then I took position 0 from your list and played in your class.

Answer 2

Paraphrasing this my article (if you want to read integer contains a full example of json deserialization):

If we stop to analyze, any Json structure is basically a Key/value map, so this is exactly how it is represented in Dart. In line 8 we created the fromJson constructor that we will use to deserialize the json, that is, to transform to an Object, by this it receives a String Map(the key will always be string) and Dynamic, which for Dart is like a generic type, any type may be in a dynamic type variable.

Basically every Map key that represents Json is a String, just as every value is at first a dynamic. You’re treating the key like int, then change to String:

PortasAbertas.fromJson(Map<String, dynamic> json) {
  i = json['i'];
  n = json['n'];
}

The process of 'serialization' works equally, also using String:

Map<String, dynamic> toJson() {
  return {
    'i':i,
    'n':n
  };
}

Answer 3

It would be that way then to deserialize ?

class PortasAbertas {
  int i;
  int n;

  PortasAbertas({this.i, this.n});

  PortasAbertas.fromJson(Map<String, dynamic> json) {
    i = json['i'];
    n = json['n'];
  }

  Map<String, dynamic> toJson() {
    return {
      'i': i,
      'n': n
    };
  }
}