json_parser 0.0.3

A generic JSON parser for Flutter using reflection.

JSON Parser for Flutter

Flutter does not provide support for auto mapping JSON to object instances. This project is an attempt to make reflection work on Flutter. Using reflection we are able to parse a JSON string and map it's values to an instance of a Dart object.

Getting started

First of all add the following dependencies to your pubspec.yaml:

dependencies:
  json_parser: 0.0.1
  build_runner: 0.8.3

Every Flutter/Dart application has a main() entry point. In that method you need to add at least the following:

void main() {
  initializeReflectable();
}

You will see that the method initializeReflectable() is not declared. That is fine, since you need to generate a code file first.

First create a build.yaml file in your Flutter application project. Then add the following content:

targets:
  $default:
    builders:
      reflectable:
        generate_for:
          - lib/main.dart
        options:
          formatted: true

lib/main.dart points to the location of the Dart class containing the main() method entry of your application.

Then open up your terminal in your project root and type the following:

flutter packages pub run build_runner build

As mentioned before, lib/main.dart specifies the folder name of the location of the class containing the main() entry. Usually in Flutter applications this is the /lib folder. If all goes well, you will see a generated .reflectable.dart file. Import the generated class in your main() entry class.

In order to make the mapping work, you need to create a new Dart object which has the same property names as your JSON. We are using the following example:

{ "name":"John", "age":30, "car":null }

Then we will use the following Dart class:

import 'package:json_parser/reflectable.dart';

@reflectable
class DataClass {
  String name;
  int age;
  String car;
}

Note the usage of @reflectable. All your classes which will be used for JSON parsing need to use this annotation.

Then you are all set and able to start the parsing. You can parse a JSON string using the following method:

DataClass instance = new DataClass();
String json = '{ "name":"John", "age":30, "car":null }';
JsonParser.parseJObject<DataClass>(json, instance);

If all goes well, instance will automatically contain all your values specified in the JSON.

You can also parse JSON arrays with a given type. However this is a bit more complex due limitations on Dart and Flutter:

String json = '[{ "name":"John", "age":30, "car":null },'
   '{ "name":"Giovanni", "age":20, "car":"Volkswagen" }]';
List<DataClass> buffer = new List<DataClass>();
int itemCount = JsonParser.getJArrayCount(json);
for (int i = 0; i < itemCount; i++) {
   buffer.add(new DataClass());
}
JsonParser.parseJArray<DataClass>(json, buffer);

TODO's

Currently the parser is only being tested on primitive properties. Later we will test and add support for more complex types such as nested objects.