Flutter load json from assets folder

1. Create a sample Flutter app

flutter create flutter_load_json_from_assets

2. Create a folder assets in the Flutter project root folder, and then create a sub-folder called data inside the assets folder, then add a json file in the data folder. Here is a sample json file: pokemon_names.json

{
  "1": {
      "id": 1,
      "name": "Bulbasaur"
  },
  "10": {
      "id": 10,
      "name": "Caterpie"
  },
  "100": {
      "id": 100,
      "name": "Voltorb"
  },
  "101": {
      "id": 101,
      "name": "Electrode"
  },
  "102": {
      "id": 102,
      "name": "Exeggcute"
  },
  "103": {
      "id": 103,
      "name": "Exeggutor"
  },
  "104": {
      "id": 104,
      "name": "Cubone"
  },
  "105": {
      "id": 105,
      "name": "Marowak"
  },
  "106": {
      "id": 106,
      "name": "Hitmonlee"
  },
  "107": {
      "id": 107,
      "name": "Hitmonchan"
  },
  "108": {
      "id": 108,
      "name": "Lickitung"
  },
  "109": {
      "id": 109,
      "name": "Koffing"
  },
  "11": {
      "id": 11,
      "name": "Metapod"
  }
}

3. In the pubspec.yaml file, specify the assets folder path.

flutter:

  assets:
    - assets/data/

4. Replace the contain in main.dart with the following.

import 'package:flutter/material.dart';
import 'dart:async' show Future;
import 'dart:convert';
import 'package:flutter/services.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Pokemons',
      home: HomePage(),
    );
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  PokemonsState createState() => PokemonsState();
}

class PokemonsState extends State {
  List _pokemons = [];

  // Read content from the json file
  Future readJson() async {
    final String response = await rootBundle.loadString('assets/data/pokemon_names.json');
    final Map data = await json.decode(response);
    List pokemons = [];
    data.forEach((final String key, final value) {
      //print("Key: {{$key}} -> value: ${value}");
      pokemons.add(value);
    });

    //print(pokemons);
    setState(() {
      _pokemons = pokemons;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        centerTitle: true,
        title: const Text(
          'Load json data',
        ),
      ),
      body: Padding(
        padding: const EdgeInsets.all(25),
        child: Column(
          children: [
            ElevatedButton(
              child: const Text('Load pokemons'),
              onPressed: readJson,
            ),

            // Display the data loaded from pokemon_names.json
            _pokemons.isNotEmpty
                ? Expanded(
              child: ListView.builder(
                itemCount: _pokemons.length,
                itemBuilder: (context, index) {
                  return Card(
                    margin: const EdgeInsets.all(10),
                    child: ListTile(
                      leading: Text(_pokemons[index]["id"].toString()),
                      title: Text(_pokemons[index]["name"]),
                    ),
                  );
                },
              ),
            )
                : Container()
          ],
        ),
      ),
    );
  }
}

5. Run the app

flutter run

Complete example in Github