Dart Package deal Tutorial – Getting Began


Discover ways to create your first Dart package deal utilizing test-driven improvement, generate documentation and publish it to pub.dev.

Usually, there are options you need to embrace in your app, however writing the code will be tedious or tough. So, you hop on to pub.dev and get the package deal that may enable you to add that characteristic, drastically saving your time and vitality.

Packages enable you to extract the code you want in order that it may be reused in the identical or a number of apps. Packages are additionally a manner you possibly can contribute to the open supply group.

Wouldn’t or not it’s nice to create your very personal package deal and share it with the group? With this tutorial, you possibly can! Alongside the way in which, you’ll discover ways to:

  • Create your first Dart package deal.
  • Publish your package deal to pub.dev.
  • Import your package deal into your Flutter app.

Getting Began

Begin by clicking the Obtain Supplies button on the prime or backside of the web page to obtain the starter mission.

On this tutorial, you’ll use Visible Studio Code, however you may also proceed with Android Studio or IntelliJ IDEA. You’ll focus extra on the Dart package deal improvement and finish with integrating your package deal into your Flutter app (Android/iOS).

Within the instance, you’ll use Genderize.io, an Open API for predicting gender based mostly on names.

Open your mission in Visible Studio Code or Android Studio, and set up your dependencies. Within the terminal, sort:

cd flutter
flutter pub get

Press Enter, and test the output:

$ cd flutter
$ flutter pub get
Working "flutter pub get" in flutter...                          2,860ms

Construct and run your mission.

Starter Genderizio project

The app has an enter discipline to enter a reputation and a button to genderize it. Enter the identify Peter and faucet Genderize.

Try to genderize Peter name

As you see, you don’t get a consequence. This performance is what you’ll implement later utilizing your newly printed Dart package deal.

Understanding Dart Packages

Dart packages are reusable code printed on the Dart package deal registry. They operate as libraries for Dart software program improvement. However there are nuances between Dart packages, particularly these of Flutter as plugins.

Dart Package deal vs. Flutter Plugin

Whereas each are technically Dart packages, a bit of nuance differentiates them.

Because the identify implies, Dart packages are made in pure Dart. You should use Dart packages for each Flutter and server-side Dart. Creating a Dart package deal is simpler than a Flutter plugin since you don’t want to check any platform-specific code. Every little thing is in Dart!

However, Flutter plugins are items of code that operate primarily as a part of the cell app. Flutter plugins normally wrap native Android/iOS code in a Dart package deal to reuse it inside the Flutter app. On this tutorial, you’ll make a Dart package deal, so your package deal can be reusable inside Flutter or easy Dart scripts.

Figuring out When to Create a Dart Package deal

Flutter has a ton of packages for even the slightest of issues.

For instance, if you wish to create a local splash, Flutter has a local splash web page package deal prepared so that you can use. Or, if you wish to create launcher photos, Flutter has a separate package deal for that too.

Nevertheless, while you don’t discover a appropriate package deal to your wants, it’s normally as a result of:

  • You’re utilizing a brand-new programming language with little group help.
  • The issue is simply too technically costly to implement — say, creating a brand new machine studying library.
  • It’s a standard downside that nobody has created a plug-and-play resolution for but.

For those who’re experiencing the final concern, you’ve discovered a superb alternative to create a brand new package deal and supply an answer to the broader group.

Writing Your First Dart Package deal

Earlier than writing your Dart package deal, you could perceive the API you’ll use. You’ll write a Dart API wrapper for Genderize.io, which predicts gender based mostly on names. Customers can submit names and get an approximate chance of that identify’s gender.

The API accepts many parameters, however you’ll solely use the identify parameter.

Use this API on to see the way it works. Faucet the hyperlink https://api.genderize.io/?identify=peter:

  "identify": "peter",
  "gender": "male",
  "chance": 0.99,
  "rely": 165452

You see the outcomes of calling this API. Now, you need to create a wrapper round it in Dart.

Making a Dart Package deal

It’s lastly time to create your first package deal. Open the terminal within the root of the starter mission, and kind:

dart create -t package deal genderizeio

Press Enter, and test the consequence:

$ dart create -t package deal genderizeio
Creating genderizeio utilizing template package deal...


Working pub get...                     1.9s
  Resolving dependencies...
  Modified 46 dependencies!

Created mission genderizeio in genderizeio! To get began, run the next instructions:

  cd genderizeio
  dart run instance/genderizeio_example.dart

You simply created the package deal! This command makes use of the Dart template and prepares base package deal information for you. It’s essential to fill them with enterprise logic.

The earlier command’s output asks you to run a couple of extra instructions, so that you’ll try this subsequent. Within the terminal, sort the next instructions:

cd genderizeio
dart run instance/genderizeio_example.dart

Here’s what’s happening within the instructions above:

  1. Modified the working listing to your newly created package deal.
  2. Run the instance mission.

Press Enter to execute the instructions.

$ dart run instance/genderizeio_example.dart
superior: true

You’ve simply executed an instance mission. It has no particular code, so that you see the easy message superior: true. You’ll replace this file later to run the Genderizeio package deal.

Understanding Dart Package deal Mission Construction

The package deal’s core consists of the next information:

  • lib/genderizeio.dart: Major interface file.
  • lib/src/genderizeio_base.dart: Core enterprise logic file. Every little thing underneath the lib/src folder is your personal implementation and shouldn’t be imported by shoppers straight. You need to export all public lessons within the lib/genderizeio.dart file.
  • pubspec.yaml: Dependencies and package deal metadata file.
  • README.md, CHANGELOG.md: Supporting information and documentation.
  • instance/genderizeio_example.dart: The instance that imports the library as if it have been a package deal and exams whether or not the app is operating.
  • check/genderizeio_test.dart: For testing the core enterprise logic.

Be aware: The testing file isn’t important for releasing a brand new Dart package deal, however it’s thought of good follow to have a set of exams earlier than deploying your package deal.

Take a look at-Pushed Improvement of the Dart Package deal

Be aware: This part is non-compulsory since you don’t have to have exams to publish a Dart package deal. For those who’d wish to dive proper into package deal implementation, be at liberty to skip to the Importing Dependencies part, the place you’ll discover a mission prepared.

You’ll use the test-driven improvement (TTD) course of to implement your small business logic. It means you could first write your exams. After that, you could write your code so that each one the exams cross.

For the reason that package deal is an API wrapper, you’ll solely do unit exams.

In testing, you’ll:

  1. Create a public interface, GenderizeAPI, to make use of the package deal.
  2. Add the tactic Future GenderizeAPI.ship(String identify) async to name Genderize.io.
  3. Return the item Genderize with the property gender in case of success or throw an exception in case of error.

Substitute check/genderizeio_test.dart with the next code:

import 'package deal:genderizeio/genderizeio.dart';
import 'package deal:mockito/annotations.dart';
import 'package deal:mockito/mockito.dart';
import 'package deal:check/check.dart';
import 'package deal:http/http.dart' as http;

import 'genderizeio_test.mocks.dart';

void essential() {
  group('Genderize.io', () {
    // 1
    ultimate shopper = MockClient();
    // 2
    ultimate genderize = GenderizeAPI(shopper);
    check('Peter is male', () async {

      // 3
        (_) async => http.Response(

      // 4
      ultimate consequence = await genderize.ship('peter');

      // 5
      count on(consequence.gender, 'male');
    // 6
    check('API exception', () async {
        (_) async => http.Response(
          "{"error":"Lacking 'identify' parameter"}',
      ultimate consequence = genderize.ship('');
      await expectLater(

You’ll see a number of code points within the editor. That’s since you haven’t added the dependencies you’ve used. You’ll repair the errors quickly by including the dependencies and producing the mock information.

Within the above code, you:

  1. Create an occasion of mock http.Shopper. This class has mocked HTTP capabilities like get and publish generated by build_runner.
  2. Create an occasion of an API wrapper based mostly on a mocked http shopper.
  3. Intercepte the community requests to return the mock information in exams.
  4. Name an API Wrapper with “Peter” because the identify parameter.
  5. Take a look at if Peter is male, with a results of “male”.
  6. Take a look at to test whether or not the wrapper returns an exception in case of error.

Subsequent, you’ll begin fixing the errors within the above code.

Including the Dependencies Via Terminal

Open the terminal and navigate genderizeio. Sort the next instructions so as to add the dependencies:

dart pub add HTTP
dart pub add build_runner --dev
dart pub add mockito --dev
dart pub get

Press Enter, and test the output.
You’ll see repeated comparable messages for every command:

Resolving dependencies...
Modified ... dependencies!

This command helps add dependencies straight by way of the terminal.

Be aware: You’ll use the Mockito package deal to mock community responses. It’s unhealthy follow to request distant information in exams. A number of points may give false errors whereas testing with an actual API, like Community Error, Server Error and Entry Error. For extra on the way to use this package deal, try this documentation.

Mockito requires you to run build_runner to generate mocks for annotated lessons. Take a look at genderizeio_test.dart and also you’ll see @GenerateMocks([http.Client]). Mockito will generate check/genderizeio_test.mocks.dart with a mocked http.Shopper class.

To generate mocks, run the next command within the terminal:

dart run build_runner construct

Press Enter, and test the output:

$ dart run build_runner construct
[INFO] Producing construct script accomplished, took 238ms
[INFO] Studying cached asset graph accomplished, took 26ms
[INFO] Checking for updates since final construct accomplished, took 296ms
[INFO] Working construct accomplished, took 6ms
[INFO] Caching finalized dependency graph accomplished, took 15ms
[INFO] Succeeded after 27ms with 0 outputs (0 actions)

Create a public interface to your package deal by changing lib/src/genderizeio_base.dart with:

import 'package deal:http/http.dart' as http;

class Genderize {
    required this.gender,

  ultimate String gender; // The gender prediction

class GenderizeAPI {
  GenderizeAPI([http.Client? client]) : shopper = shopper ?? http.Shopper();

  /// Http shopper dependency to ship community requests.
  ultimate http.Shopper shopper;

  Future<Genderize> ship(String identify) async {
    return Genderize(gender: 'unknown');

Now all of the errors have been mounted

This minimal public interface lets shoppers name your package deal and run exams on it.

Rerun the exams utilizing dart check check/genderizeio_test.dart:

$ dart check check/genderizeio_test.dart 
Constructing package deal executable... (2.5s)
Constructed check:check.
00:00 +0 -1: Genderize.io Peter is male [E]                                                                                                                       
  Anticipated: 'male'
    Precise: 'unknown'
     Which: is completely different.
            Anticipated: male
              Precise: unknown
             Differ at offset 0
  package deal:test_api                 count on
  check/genderizeio_test.dart 55:7  essential.<fn>.<fn>
00:00 +0 -2: Genderize.io API exception [E]                                                                                                                       
  Anticipated: throws <Occasion of 'Exception'>
    Precise: <Occasion of 'Future<Genderize>'>
     Which: emitted <Occasion of 'Genderize'>
  check/genderizeio_test.dart 67:7  essential.<fn>.<fn>
00:00 +0 -2: Some exams failed.                                                                                                                                   

Take into account enabling the flag chain-stack-traces to obtain extra detailed exceptions.
For instance, 'dart check --chain-stack-traces'.

Exams failed, however they have been alleged to fail.

You completed the primary a part of the TTD course of. The following sections enable you to implement enterprise logic so that each one the exams can cross.

Importing Dependencies

Be aware: For those who completed the earlier part, Take a look at-Pushed Improvement of the Dart Package deal, you have already got all of the dependencies that you just’ll want. Be at liberty to go on to the following part.

Since you could work together with a REST API, you could add a dependency to speak with HTTP companies.

Open pubspec.yaml, and add the next line within the dependencies part:

  http: ^0.13.4

Open your terminal, and set up your Dart dependencies:

dart pub get

Press Enter, and test the consequence:

$ dart pub get
Resolving dependencies... 
Received dependencies!

The above code provides all of the packages talked about in pubspec.yaml into our mission.

Now that you’ve the HTTP package deal you possibly can write HTTP capabilities to get a response from Genderize API.

Dart Package deal Enterprise Logic

To cross the exams, you could implement the objectives you beforehand outlined. Go to lib/src/genderizeio_base.dart and substitute its content material with:

import 'dart:async';
import 'dart:convert';

import 'package deal:http/http.dart' as http;

class Genderize {
    required this.identify,
    required this.gender,
    required this.chance,
    required this.rely,
  ultimate String identify; /// The identify submitted by way of the question parameters
  ultimate String gender; /// The gender prediction
  ultimate double chance; /// The chance of the prediction validity
  ultimate int rely; /// The variety of names within the database
  // 2
  manufacturing unit Genderize.fromJson(Map<String, dynamic> information) {
    ultimate identify = information['name'] as String;
    ultimate gender = information['gender'] as String;
    ultimate chance = information['probability'] as double;
    ultimate rely = information['count'] as int;

    return Genderize(
      identify: identify,
      gender: gender,
      chance: chance,
      rely: rely,

// 3
class GenderizeAPI {
  GenderizeAPI([http.Client? client]) : shopper = shopper ?? http.Shopper();

  /// Http shopper dependency to ship community requests.
  ultimate http.Shopper shopper;
  // 4
  Future<Genderize> ship(String identify) async {
    ultimate response = await shopper.get(Uri.parse('https://api.genderize.io?identify=$identify'));

    if (response.statusCode == 200) {
      // 5
      ultimate json = jsonDecode(response.physique) as Map<String, dynamic>;
      return Genderize.fromJson(json);
    } else {
      // 6
      throw Exception('Didn't load gender');

Right here’s a code breakdown:

  1. You add a mannequin class named Genderize for the API response.
  2. fromJson returns a Genderize mannequin object.
  3. GenderizeAPI Class is a main wrapper interface.
  4. A future ship(String identify) methodology to name an API which returns a Genderize object or throws an exception if the gender fails to load.
  5. You come back the Genderize occasion in case of success.
  6. Or throw an exception in case of error.

You fulfilled all of your objectives for TTD. Now, open the terminal and rerun the exams with the next command:

dart check

Press Enter, and run exams:

$ dart check 
00:01 +2: All exams handed!        

It really works! Your Dart package deal is working nicely and has handed the exams.

Exporting Your Dart Package deal

After implementing your Dart mission, you could confirm that your package deal is exportable and importable. lib/genderizeio.dart would be the essential entry level to export the mission.

Go to lib/genderizeio.dart, and test in case your file seems just like the code beneath:

library genderizeio;

export 'src/genderizeio_base.dart';

This file defines that each one public variables from src/genderizeio_base.dart are seen to anybody who imports your package deal utilizing import 'package deal:genderizeio/genderizeio.dart';.

Now it’s time to test the package deal you created. You’ll use the instance app for this.

Go to instance/genderizeio_example.dart, and substitute its content material with:

import 'package deal:genderizeio/genderizeio.dart';

void essential() async {
  ultimate genderize = GenderizeAPI();
  ultimate consequence = await genderize.ship('peter');
  print('${consequence.identify}: ${consequence.gender}');

Within the above code, you:

  • Create a GenderizeAPI occasion object named genderize. Now the Genderize strategies can be accessible.
  • Name the ship operate from GenderizeAPI, which takes a reputation parameter and returns a gender object.
  • Print within the console the genderize object identify and gender.

For those who’ve carried out the testing half, you’ll notice that is much like the unit testing half.

Run the instance app to verify the above code is working.

Within the terminal, run the next command to run the instance app:

dart run instance/genderizeio_example.dart

Press Enter, and test the output:

$ dart run instance/genderizeio_example.dart
peter: male

You’ll get the above output. The instance app is operating and also you get an output that tells Peter’s gender.

Publishing Your Dart Package deal

Your package deal is sort of prepared. It solely wants a couple of ending touches earlier than it goes stay. First, you could create fundamental documentation to inform builders what your package deal does and the way they’ll use it.

For simplicity’s sake, change the package deal’s metadata identify to my_genderizeio in pubspec.yaml.

Your pubspec.yaml ought to appear like the screenshot beneath:

Change the package name in pubspec.yaml

Now you’ll see that your instance app and genderizeio_test.dart are throwing errors. It’s because you modified the package deal identify and it will possibly’t discover the GenderizeAPI class.

To repair this concern, change the import as observe in each information:

import 'package deal:my_genderizeio/genderizeio.dart';

Creating the Fundamental Documentation README.md

The documentation for the package deal shouldn’t be too lengthy and will be easy because the package deal is principally a REST API wrapper. The Dart template fills within the README.md with some common sections like Getting began and Utilization. Undergo the file and fill within the sections with info.

Fill within the Utilization part with directions on how builders can use your package deal:

# Utilization
To make use of the `Genderize.io` package deal, you possibly can merely import the `GenderizeAPI` class and name the `ship` operate:
ultimate genderize = GenderizeAPI();
ultimate consequence = await genderize.ship('peter');
print('${consequence.identify}: ${consequence.gender}');

README.md directions are a really vital a part of the documentation. They inform builders how a package deal may also help them and the way to use it.

Subsequent, edit your pubspec.yaml and add a brand new repository part. You’ll be able to’t publish the library if it isn’t hosted in a public repository, like GitHub:

repository: https://github.com/your/repository

Your pubspec.yaml ought to appear like this:

Add repository section to pubspec.yaml


To efficiently publish your package deal, you could embrace a license to your library. The license grants permission to different customers and states how they’ll use the package deal and underneath whose identify the package deal is registered. For those who aren’t acquainted with licenses, copy the MIT license and paste it into the LICENSE file.

Producing Package deal Documentation

Be aware: This part is non-compulsory since you don’t have to have documentation to publish a Dart package deal. Be at liberty to skip to the Publishing Package deal Dry Run part, the place you’ll discover ways to check your package deal metadata.

Dart has a really useful software for producing documentation utilizing ahead slashs. You employ three forwards slashes earlier than the operate /// and add info to your code. This info can be displayed when the consumer hovers their cursor over the operate.

Remark your lib/src/genderizeio_base.dart to enhance the standard of the code. Right here’s an instance of what it could appear like:

Example of documentation

Open Terminal and kind the next command:

dart doc

Press Enter, and test the output:

$ dart doc
Documenting my_genderizeio...
Initialized dartdoc with 196 libraries
Producing docs for library genderizeio from package deal:my_genderizeio/genderizeio.dart...
no points discovered
Documented 1 public library in 8.8 seconds
Success! Docs generated into genderizeio/doc/api

Examine the mission folder; it has a brand new listing named doc.

Open the index file doc/api/index.html in a browser, and navigate to the ship methodology documentation.

Generated documentation

You’ll now see the documentation for the ship methodology with all feedback you added to the code.

Be aware: To enhance your documentation, see the official information with superior formatting options.

Importing Your Package deal Regionally

Usually, you add the package deal into your pubspec.yaml and run flutter pub get. This command fetches the package deal from the web repo and provides it to your mission.

You’ll have observed that you just haven’t deployed your package deal anyplace on-line. For the mission to fetch the package deal, you could give the package deal’s path, or the place the package deal is positioned regionally in your machine.

Go to flutter/pubspec.yaml, and import the package deal regionally by including the trail of the adjoining genderizeio folder:

    path: ../genderizeio

Open Terminal, change the listing to your Flutter mission, and run flutter pub get to confirm the set up is right. Then, test the output:

$ flutter pub get
Working "flutter pub get" in flutter...                            225ms

Go to flutter/essential.dart and substitute the _predictGender methodology with the next code:

void _predictGender() async {
  setState(() {
    _gender = _genderLoading;

  ultimate genderize = GenderizeAPI();
  ultimate consequence = await genderize.ship('peter');
  setState(() {
    _gender="might be ${consequence.gender}";

Import the genderizeio package deal when IDE exhibits you an error and suggests importing the library.

Construct and run the mission.

Use package locally in Flutter project

You simply used your package deal in your app!

Publishing a Package deal Dry Run

Now that you just’ve examined your package deal, it’s able to go public.

Earlier than you publish your Dart package deal, do a dry run to check whether or not the whole lot goes in keeping with plan. Open Terminal, go to the genderizeio folder, and kind the next command:

dart pub publish --dry-run

Press Enter, and test the output. Your package deal ought to return a message:

$ dart pub publish --dry-run
Publishing my_genderizeio 1.0.0 to https://pub.dartlang.org:
|-- README.md
|-- analysis_options.yaml
|-- doc
|    -- api
|       |-- __404error.html
|       |-- classes.json
|       |-- genderizeio
|       |   |-- Genderize
|       |   |   |-- Genderize.fromJson.html
|       |   |   |-- Genderize.html
|       |   |   |-- rely.html
|       |   |   |-- gender.html
|       |   |   |-- identify.html
|       |   |   |-- chance.html
|       |   |-- Genderize-class.html
|       |   |-- GenderizeAPI
|       |   |   |-- GenderizeAPI.html
|       |   |    -- ship.html
|       |   |-- GenderizeAPI-class.html
|       |    -- genderizeio-library.html
|       |-- index.html
|       |-- index.json
|       |-- static-assets
|           |-- favicon.png
|           |-- github.css
|           |-- spotlight.pack.js
|           |-- play_button.svg
|           |-- readme.md
|           |-- script.js
|           |-- types.css
|-- instance
|    -- genderizeio_example.dart
|-- lib
|   |-- genderizeio.dart
|    -- src
|        -- genderizeio_base.dart
|-- pubspec.yaml
|-- check
     -- genderizeio_test.dart

Package deal has 0 warnings.
The server could implement extra checks.

The response seems good, which means the package deal is able to be printed.

In case your package deal is lacking some information, just like the license, it’ll throw an error. So, it’s vital that the above command passes with none errors.

Publishing Dart Packages

Now, it’s time to attempt publishing it for actual! Open Terminal, and kind the next command:

dart pub publish

Press Enter, and test the output. If the whole lot goes nicely, you’ll obtain:

Publishing my_genderizeio 1.0.0 to https://pub.dartlang.org:
|-- README.md
|-- analysis_options.yaml
|-- instance
|    -- genderizeio_example.dart
|-- doc ...
|-- lib
|   |-- genderizeio.dart
|   |-- src
|        -- genderizeio_base.dart
|-- pubspec.yaml
|-- check
    |-- genderizeio_test.dart

Package deal has 0 warnings.
The server could implement extra checks.

Nice, you printed your first package deal!

Importing Your Dart Package deal as Dependencies

To import your package deal inside your Flutter app, open flutter/pubspec.yaml once more and alter the dependency to an exterior one:

my_genderizeio: 1.0.0

Run flutter pub get, and also you’ll be good to go!

Construct and run your Flutter mission.

Flutter project with external package

The place to Go From Right here?

You’ll be able to obtain the educational supplies utilizing the Obtain Supplies button on the highest or backside of the web page to match your outcomes.

Making a Dart package deal from scratch is a reasonably fundamental course of, and it’s studying step to creating and studying Dart total.

For those who’re desirous about exploring Dart some extra, try:

I hope you loved making your first Dart package deal and located this tutorial useful. Please be part of the discussion board dialogue beneath when you’ve got any questions or feedback.


Leave a Reply