Code generation for immutable classes that has a simple syntax/API without compromising on the features.

While there are many code-generators available to help you deal with immutable objects, they usually come with a trade-off. Either they have a simple syntax but lack features, or they have very advanced features but with complex syntax.

Installing and Using Freezed package

Add this to your package's pubspec.yaml file:

You can then install packages from the command line:

Example

Now you can use it in your Dart code by importing it like this:

Write the following code

To generate the code type the following command

Ignore lint warnings on generated files

It is likely that the code generated by Freezed will cause your linter to report warnings.

The solution to this problem is to tell the linter to ignore generated files, by modifying your analysis_options.yaml:

It is hard to think of a mobile app that doesn’t need to communicate with a web server or easily store structured data at some point. When making network-connected apps, the chances are that it needs to consume some good old JSON, sooner or later.

In case you're not familiar with the term data class, it's simply a class with value equality, copyWith method, its fields are immutable and it usually easily supports serialization. Also, if you're familiar with Kotlin, you know that you can heavily cut down on the boilerplate by defining fields directly in the constructor like this:

data class User(val name: String, val age: Int)

instead of this

@immutable
class User {
  final String name;
  final int age;

  User(this.name, this.age);

  User copyWith({
    String name,
    int age,
  }) {
    return User(
      name ?? this.name,
      age ?? this.age,
    );
  }

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

    return o is User && o.name == name && o.age == age;
  }

  @override
  int get hashCode => name.hashCode ^ age.hashCode;
}

instead of coding boilerplate freezed does all this with a few keystrokes

import 'package:meta/meta.dart';

part 'freezed_classes.freezed.dart';

@immutable
abstract class User with _$User {
  const factory User(String name, int age) = _User;
}

In this section we will be Working on Creating the models of the Products features and the following will be covered.

• Introduction to Freezed

• Introduction to JSON annotation

• Creating Products model

After installing and experimenting on the freezed package, now let's create producs model.

First, create the "product.dart" file under src/product/model/product/ with the following code.

import 'package:flutter/foundation.dart';
import 'package:freezed_annotation/freezed_annotation.dart';
import 'package:techamp_flutter_shopping_app/app.dart';

part 'product.freezed.dart';
part 'product.g.dart';

@freezed
abstract class Product with _$Product {
  const factory Product({
    @required int id,
    @required String title,
    @required String image,
    @required double price,
    @required String description,
    @required @CategoryConverter() ProductCategory category,
  }) = _Product;

  factory Product.fromJson(Map<String, dynamic> json) =>
      _$ProductFromJson(json);
}

After this run, the command "pub run build_runner build" on the terminal of the project to generate the product source code. After running it you should see "product.freezed.dart" and "product.g.dart" files next to it where the generated source code is written.

Installing and Using json_serializable and json_annotation packages

Add this to your package's pubspec.yaml file:

You can then install packages from the command line:

Example

Now you can use it in your Dart code by importing it like this:

Write the following code

To generate the code type the following command

Ignore lint warnings on generated files

It is likely that the code generated by Json_Serializer will cause your linter to report warnings.

The solution to this problem is to tell the linter to ignore generated files, by modifying your analysis_options.yaml: