Json Mapping-Data Class Generator-Progress Indicator in Flutter

if we have to get data in json formate than we first have to map the data in catalog.dart file like this

import 'dart:convert';

class CatalogModel {
  static List<Item> items;
}

class Item {
  final int id;
  final String name;
  final String desc;
  final num price;
  final String color;
  final String image;

  Item({
    this.id,
    this.name,
    this.desc,
    this.price,
    this.color,
    this.image,
  });

  Item copyWith({
    int id,
    String name,
    String desc,
    num price,
    String color,
    String image,
  }) {
    return Item(
      id: id ?? this.id,
      name: name ?? this.name,
      desc: desc ?? this.desc,
      price: price ?? this.price,
      color: color ?? this.color,
      image: image ?? this.image,
    );
  }

  Map<String, dynamic> toMap() {
    return {
      'id': id,
      'name': name,
      'desc': desc,
      'price': price,
      'color': color,
      'image': image,
    };
  }

  factory Item.fromMap(Map<String, dynamic> map) {
    if (map == null) return null;

    return Item(
      id: map['id'],
      name: map['name'],
      desc: map['desc'],
      price: map['price'],
      color: map['color'],
      image: map['image'],
    );
  }

  String toJson() => json.encode(toMap());

  factory Item.fromJson(String source) => Item.fromMap(json.decode(source));

  @override
  String toString() {
    return 'Item(id: $id, name: $name, desc: $desc, price: $price, color: $color, image: $image)';
  }

  @override
  bool operator ==(Object o) {
    if (identical(this, o)) return true;

    return o is Item &&
        o.id == id &&
        o.name == name &&
        o.desc == desc &&
        o.price == price &&
        o.color == color &&
        o.image == image;
  }

  @override
  int get hashCode {
    return id.hashCode ^
        name.hashCode ^
        desc.hashCode ^
        price.hashCode ^
        color.hashCode ^
        image.hashCode;
  }
}
In home page load this json file data

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'dart:convert';
import 'package:flutter_catalog/models/catalog.dart';
import 'package:flutter_catalog/widgets/drawer.dart';
import 'package:flutter_catalog/widgets/item_widget.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  final int days = 30;

  final String name = "Codepur";

  @override
  void initState() {
    super.initState();
    loadData();
  }

  loadData() async {
    await Future.delayed(Duration(seconds: 2));
    final catalogJson =
        await rootBundle.loadString("assets/files/catalog.json");
    final decodedData = jsonDecode(catalogJson);
    var productsData = decodedData["products"];
    CatalogModel.items = List.from(productsData)
        .map<Item>((item) => Item.fromMap(item))
        .toList();
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Catalog App"),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: (CatalogModel.items != null && CatalogModel.items.isNotEmpty)
            ? ListView.builder(
                itemCount: CatalogModel.items.length,
                itemBuilder: (context, index) => ItemWidget(
                  item: CatalogModel.items[index],
                ),
              )
            : Center(
                child: CircularProgressIndicator(),
              ),
      ),
      drawer: MyDrawer(),
    );
  }
}