Mapping JSON into Class Objects

Question

I am trying to map my JSON file into a class object, and then update the cards based on the newly received JSON.

My JSON structure is like this

 {
        "$class": "FirstCard",
        "id": "1",
        "description": "I am card number one",
        "Role": "attack",
        "score": 0,
        "tag": [
            "string"
        ],................}

my Class looks like this:

  class CardInfo {
  //Constructor
  String id;
  String description;
  String role;
  int score;

}

How can I map the values in my JSON file into the fields of objects created from CardInfo class?

Update

the following trial prints null at ci.description, does this mean the object was never created ?

const jsonCodec = const JsonCodec
_loadData() async {
  var url = 'myJsonURL';
  var httpClient  = createHttpClient();
  var response =await httpClient.get(url);
  print ("response" + response.body);
  Map cardInfo = jsonCodec.decode(response.body);
  var ci = new CardInfo.fromJson(cardInfo);
  print (ci.description); //prints null
}

Update2

Printing cardInfo gives the following:

{$class: FirstCard, id: 1, description: I am card number one,........}

Note that it resembles the original JSON but without the double quotes on string values.

Answer 1

class CardInfo {
  //Constructor
  String id;
  String description;
  String role;
  int score;

  CardInfo.fromJson(Map json) {
    this.id = json['id'];
    this.description = json['description'];
    this.role = json['Role'];
    this.score = json['score'];
  }
}

var ci = new CardInfo.fromJson(myJson); 

You can use source generation tools like https://github.com/dart-lang/source_gen https://pub.dartlang.org/packages/json_serializable to generate the serialization and deserialization code for you.

If you prefer using immutable classes https://pub.dartlang.org/packages/built_value is a good bet.

Answer 2

If you want to get your JSON from a url do as follows:

import 'dart:convert';

_toObject() async {
  var url = 'YourJSONurl';
  var httpClient  = createHttpClient();
  var response =await httpClient.get(url);
  Map cardInfo = JSON.decode(response.body);
  var ci = new CardInfo.fromJson(cardInfo);
}

Please refer to the main answer if you want to know how to setup your class so that your JSON fields can be mapped to it. It is very helpful.