How to do it...

In this recipe, we will use constants instead of typing in the keys of each field of the JSON data. The starting code is at the end of the previous recipe:

1. At the top of the pizza.dart file, add the constants that we will need later within the Pizza class:

const keyId = 'id';
const keyName = 'pizzaName';
const keyDescription = 'description';
const keyPrice = 'price';
const keyImage = 'imageUrl';

2. In the Pizza.fromJson constructor, remove the strings for the JSON object and add the constants instead:

Pizza.fromJson(Map<String, dynamic> json) {
this.id = (json[keyId] != null) ? int.tryParse(json['id'].toString()) : 0;
this.pizzaName =
(json[keyName] != null) ? json[keyName].toString() : '';
this.description = (json[keyDescription] != null) ? json[keyDescription].toString() : '';
this.price = (json[keyPrice] != null && double.tryParse(json[keyPrice].toString()) != null) ? json[keyPrice...