flutter_clean_architecture

Description:

flutter clean architecture

flutter_clean_architecture Package #

Overview #
A Flutter package that makes it easy and intuitive to implement Uncle Bob's Clean Architecture in Flutter. This package provides basic classes that are tuned to work with Flutter and are designed according to the Clean Architecture.
Installation #
1. Depend on It #
Add this to your package's pubspec.yaml file:

dependencies:
flutter_clean_architecture: ^6.0.1

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2. Install it #
You can install packages from the command line:
with Flutter:
$ flutter packages get
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Alternatively, your editor might support flutter packages get. Check the docs for your editor to learn more.
3. Import it #
Now in your Dart code, you can use:
import 'package:flutter_clean_architecture/flutter_clean_architecture.dart';
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Flutter Clean Architecture Primer #
Introduction #
It is architecture based on the book and blog by Uncle Bob. It is a combination of concepts taken from the Onion Architecture and other architectures. The main focus of the architecture is separation of concerns and scalability. It consists of four main modules: App, Domain, Data, and Device.
The Dependency Rule #
Source code dependencies only point inwards. This means inward modules are neither aware of nor dependent on outer modules. However, outer modules are both aware of and dependent on inner modules. Outer modules represent the mechanisms by which the business rules and policies (inner modules) operate. The more you move inward, the more abstraction is present. The outer you move the more concrete implementations are present. Inner modules are not aware of any classes, functions, names, libraries, etc.. present in the outer modules. They simply represent rules and are completely independent from the implementations.
Layers #
Domain
The Domain module defines the business logic of the application. It is a module that is independent from the development platform i.e. it is written purely in the programming language and does not contain any elements from the platform. In the case of Flutter, Domain would be written purely in Dart without any Flutter elements. The reason for that is that Domain should only be concerned with the business logic of the application, not with the implementation details. This also allows for easy migration between platforms, should any issues arise.
Contents of Domain
Domain is made up of several things.

Entities

Enterprise-wide business rules
Made up of classes that can contain methods
Business objects of the application
Used application-wide
Least likely to change when something in the application changes


Usecases

Application-specific business rules
Encapsulate all the usecases of the application
Orchestrate the flow of data throughout the app
Should not be affected by any UI changes whatsoever
Might change if the functionality and flow of application change


Repositories

Abstract classes that define the expected functionality of outer layers
Are not aware of outer layers, simply define expected functionality

E.g. The Login usecase expects a Repository that has login functionality


Passed to Usecases from outer layers



Domain represents the inner-most layer. Therefore, it the most abstract layer in the architecture.
App
App is the layer outside Domain. App crosses the boundaries of the layers to communicate with Domain. However, the Dependency Rule is never violated. Using polymorphism, App communicates with Domain using inherited class: classes that implement or extend the Repositories present in the Domain layer. Since polymorphism is used, the Repositories passed to Domain still adhere to the Dependency Rule since as far as Domain is concerned, they are abstract. The implementation is hidden behind the polymorphism.
Contents of App
Since App is the presentation layer of the application, it is the most framework-dependent layer, as it contains the UI and the event handlers of the UI. For every page in the application, App defines at least 3 classes: a Controller, a Presenter, and a View.

View

Represents only the UI of the page. The View builds the page's UI, styles it, and depends on the Controller to handle its events. The View has-a Controller.
In the case of Flutter

The View is comprised of 2 classes

One that extends View, which would be the root Widget representing the View
One that extends ViewState with the template specialization of the other class and its Controller.


The ViewState contains the view getter, which is technically the UI implementation
StatefulWidget contains the State as per Flutter
The StatefulWidget only serves to pass arguments to the State from other pages such as a title etc.. It only instantiates the State object (the ViewState) and provides it with the Controller it needs through it's consumer.
The StatefulWidget has-a State object (the ViewState) which has-a Controller
In summary, both the StatefulWidget and the State are represented by a View and ViewState of the page.
The ViewState class maintains a GlobalKey that can be used as a key in its scaffold. If used, the Controller can easily access it via getState() in order to show snackbars and other dialogs. This is helpful but optional.




Controller

Every ViewState has-a Controller. The Controller provides the needed member data of the ViewState i.e. dynamic data. The Controller also implements the event-handlers of the ViewState widgets, but has no access to the Widgets themselves. The ViewState uses the Controller, not the other way around. When the ViewState calls a handler from the Controller, refreshUI() can be called to update the view.
Every Controller extends the Controller abstract class, which implements WidgetsBindingObserver. Every Controller class is responsible for handling lifecycle events for the View and can override:

void onInActive()
void onPaused()
void onResumed()
void onDetached()
void onDisposed()
void onReassembled()
void onDidChangeDependencies()
void onInitState()
etc..


Also, every Controller has to implement initListeners() that initializes the listeners for the Presenter for consistency.
The Controller has-a Presenter. The Controller will pass the Repository to the Presenter, which it communicate later with the Usecase. The Controller will specify what listeners the Presenter should call for all success and error events as mentioned previously. Only the Controller is allowed to obtain instances of a Repository from the Data or Device module in the outermost layer.
The Controller has access to the ViewState and can refresh the ControlledWidgets via refreshUI().


Presenter

Every Controller has-a Presenter. The Presenter communicates with the Usecase as mentioned at the beginning of the App layer. The Presenter will have members that are functions, which are optionally set by the Controller and will be called if set upon the Usecase sending back data, completing, or erroring.
The Presenter is comprised of two classes

Presenter e.g. LoginPresenter

Contains the event-handlers set by the Controller
Contains the Usecase to be used
Initializes and executes the usecase with the Observer<T> class and the appropriate arguments. E.g. with username and password in the case of a LoginPresenter


A class that implements Observer<T>

Has reference to the Presenter class. Ideally, this should be an inner class but Dart does not yet support them.
Implements 3 functions

onNext(T)
onComplete()
onError()


These 3 methods represent all possible outputs of the Usecase

If the Usecase returns an object, it will be passed to onNext(T).
If it errors, it will call onError(e).
Once it completes, it will call onComplete().


These methods will then call the corresponding methods of the Presenter that are set by the Controller. This way, the event is passed to the Controller, which can then manipulate data and update the ViewState






Extra

Utility classes (any commonly used functions like timestamp getters etc..)
Constants classes (const strings for convenience)
Navigator (if needed)



Data
Represents the data-layer of the application. The Data module, which is a part of the outermost layer, is responsible for data retrieval. This can be in the form of API calls to a server, a local database, or even both.
Contents of Data

Repositories

Every Repository should implement Repository from the Domain layer.
Using polymorphism, these repositories from the data layer can be passed across the boundaries of layers, starting from the View down to the Usecases through the Controller and Presenter.
Retrieve data from databases or other methods.
Responsible for any API calls and high-level data manipulation such as

Registering a user with a database
Uploading data
Downloading data
Handling local storage
Calling an API




Models (not a must depending on the application)

Extensions of Entities with the addition of extra members that might be platform-dependent. For example, in the case of local databases, this can be manifested as an isDeleted or an isDirty entry in the local database. Such entries cannot be present in the Entities as that would violate the Dependency Rule since Domain should not be aware of the implementation.
In the case of our application, models in the Data layer will not be necessary as we do not have a local database. Therefore, it is unlikely that we will need extra entries in the Entities that are platform-dependent.


Mappers

Map Entity objects to Models and vice-versa.
Static classes with static methods that receive either an Entity or a Model and return the other.
Only necessary in the presence of Models


Extra

Utility classes if needed
Constants classes if needed



Device
Part of the outermost layer, Device communicates directly with the platform i.e. Android and iOS. Device is responsible for Native functionality such as GPS and other functionality present within the platform itself like the filesystem. Device calls all Native APIs.
Contents of Data

Devices

Similar to Repositories in Data, Devices are classes that communicate with a specific functionality in the platform.
Passed through the layers the same way Repositories are pass across the boundaries of the layer: using polymorphism between the App and Domain layer. That means the Controller passes it to the Presenter then the Presenter passes it polymorphically to the Usecase, which receives it as an abstract class.


Extra

Utility classes if needed
Constants classes if needed



Usage #
Folder structure #
lib/
app/ <--- application layer
pages/ <-- pages or screens
login/ <-- some page in the app
login_controller.dart <-- login controller extends `Controller`
login_presenter.dart <-- login presenter extends `Presenter`
login_view.dart <-- login view, 2 classes extend `View` and `ViewState` resp.
widgets/ <-- custom widgets
utils/ <-- utility functions/classes/constants
navigator.dart <-- optional application navigator
data/ <--- data layer
repositories/ <-- repositories (retrieve data, heavy processing etc..)
data_auth_repo.dart <-- example repo: handles all authentication
helpers/ <-- any helpers e.g. http helper
constants.dart <-- constants such as API keys, routes, urls, etc..
device/ <--- device layer
repositories/ <--- repositories that communicate with the platform e.g. GPS
utils/ <--- any utility classes/functions
domain/ <--- domain layer (business and enterprise) PURE DART
entities/ <--- enterprise entities (core classes of the app)
user.dart <-- example entity
manager.dart <-- example entity
usecases/ <--- business processes e.g. Login, Logout, GetUser, etc..
login_usecase.dart <-- example usecase extends `UseCase` or `CompletableUseCase`
repositories/ <--- abstract classes that define functionality for data and device layers
main.dart <--- entry point

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Example Code #
Checkout a small example here and a full application built here.
View and ControlledWidgetBuilder
import 'package:flutter_clean_architecture/flutter_clean_architecture.dart';
class CounterPage extends View {
@override
// Dependencies can be injected here
State<StatefulWidget> createState() => CounterState();
}

class CounterState extends ViewState<CounterPage, CounterController> {
CounterState() : super(CounterController());

@override
Widget get view => MaterialApp(
title: 'Flutter Demo',
home: Scaffold(
key: globalKey, // using the built-in global key of the `View` for the scaffold or any other
// widget provides the controller with a way to access them via getContext(), getState(), getStateKey()
body: Column(
children: <Widget>[
Center(
// show the number of times the button has been clicked
child: ControlledWidgetBuilder<CounterController>(
builder: (context, controller) {
return Text(controller.counter.toString());
}
),
),
// you can refresh manually inside the controller
// using refreshUI()
ControlledWidgetBuilder<CounterController>(
builder: (context, controller) {
return MaterialButton(onPressed: controller.increment);
}
),
],
),
),
);
}
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Responsive view state
To deal with screens on flutter web, you can take advantage of the responsive view state,
that abstracts the main web apps breakpoints (desktop, tablet and mobile) to ease development
for web with flutter_clean_architecture
For example:
import 'package:flutter_clean_architecture/flutter_clean_architecture.dart';
class CounterPage extends View {
@override
// Dependencies can be injected here
State<StatefulWidget> createState() => CounterState();
}

class CounterState extends ResponsiveViewState<CounterPage, CounterController> {
CounterState() : super(CounterController());

Widget AppScaffold({Widget child}) {
return MaterialApp(
title: 'Flutter Demo',
home: Scaffold(
key: globalKey, // using the built-in global key of the `View` for the scaffold or any other
// widget provides the controller with a way to access them via getContext(), getState(), getStateKey()
body: child
),
);
}

@override
ViewBuilder get mobileView => AppScaffold(
child: Column(
children: <Widget>[
// you can refresh manually inside the controller
// using refreshUI()
ControlledWidgetBuilder<CounterController>(
builder: (context, controller) {
return Text('Counter on mobile view ${controller.counter.toString()}');
}
),
],
)
);

@override
ViewBuilder get tabletBuilder => AppScaffold(
child: Column(
children: <Widget>[
// you can refresh manually inside the controller
// using refreshUI()
ControlledWidgetBuilder<CounterController>(
builder: (context, controller) {
return Text('Counter on tablet view ${controller.counter.toString()}');
}
),
],
)
);

@override
ViewBuilder get desktopBuilder => AppScaffold(
child: Row(
children: <Widget>[
// you can refresh manually inside the controller
// using refreshUI()
ControlledWidgetBuilder<CounterController>(
builder: (context, controller) {
return Text('Counter on desktop view ${controller.counter.toString()}');
}
),
],
)
);
}
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Widgets with Common Controller
In the event that multiple widgets need to use the same Controller of a certain Page,
the Controller can be retrieved inside the children widgets of that page via
FlutterCleanArchitecture.getController<HomeController>(context).
For example:

import '../pages/home/home_controller.dart';
import 'package:flutter/material.dart';
import 'package:flutter_clean_architecture/flutter_clean_architecture.dart';

class HomePageButton extends StatelessWidget {
final String text;
HomePageButton({@required this.text});

@override
Widget build(BuildContext context) {
// use a common controller assuming HomePageButton is always a child of Home
HomeController controller =
FlutterCleanArchitecture.getController<HomeController>(context);
return GestureDetector(
onTap: controller.buttonPressed,
child: Container(
height: 50.0,
alignment: FractionalOffset.center,
decoration: BoxDecoration(
color: Color.fromRGBO(230, 38, 39, 1.0),
borderRadius: BorderRadius.circular(25.0),
),
child: Text(
text,
style: const TextStyle(
color: Colors.white,
fontSize: 20.0,
fontWeight: FontWeight.w300,
letterSpacing: 0.4),
),
),
);
}
}

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Controller
import 'package:flutter_clean_architecture/flutter_clean_architecture.dart';

class CounterController extends Controller {
int counter;
final LoginPresenter presenter;
CounterController() : counter = 0, presenter = LoginPresenter(), super();

void increment() {
counter++;
}

/// Shows a snackbar
void showSnackBar() {
ScaffoldState scaffoldState = getState(); // get the state, in this case, the scaffold
scaffoldState.showSnackBar(SnackBar(content: Text('Hi')));
}

@override
void initListeners() {
// Initialize presenter listeners here
// These will be called upon success, failure, or data retrieval after usecase execution
presenter.loginOnComplete = () => print('Login Successful');
presenter.loginOnError = (e) => print(e);
presenter.loginOnNext = () => print("onNext");
}

void login() {
// pass appropriate credentials here
// assuming you have text fields to retrieve them and whatnot
presenter.login();
}
}

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Presenter
import 'package:flutter_clean_architecture/flutter_clean_architecture.dart';

class LoginPresenter() {

Function loginOnComplete; // alternatively `void loginOnComplete();`
Function loginOnError;
Function loginOnNext; // not needed in the case of a login presenter

final LoginUseCase loginUseCase;
// dependency injection from controller
LoginPresenter(authenticationRepo): loginUseCase = LoginUseCase(authenticationRepo);

/// login function called by the controller
void login(String email, String password) {
loginUseCase.execute(_LoginUseCaseObserver(this), LoginUseCaseParams(email, password));
}

/// Disposes of the [LoginUseCase] and unsubscribes
@override
void dispose() {
_loginUseCase.dispose();
}
}

/// The [Observer] used to observe the `Stream` of the [LoginUseCase]
class _LoginUseCaseObserver implements Observer<void> {

// The above presenter
// This is not optimal, but it is a workaround due to dart limitations. Dart does
// not support inner classes or anonymous classes.
final LoginPresenter loginPresenter;

_LoginUseCaseObserver(this.loginPresenter);

/// implement if the `Stream` emits a value
// in this case, unnecessary
void onNext(_) {}

/// Login is successful, trigger event in [LoginController]
void onComplete() {
// any cleaning or preparation goes here
assert(loginPresenter.loginOnComplete != null);
loginPresenter.loginOnComplete();

}

/// Login was unsuccessful, trigger event in [LoginController]
void onError(e) {
// any cleaning or preparation goes here
assert(loginPresenter.loginOnError != null);
loginPresenter.loginOnError(e);
}
}

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UseCase
import 'package:flutter_clean_architecture/flutter_clean_architecture.dart';

// In this case, no parameters were needed. Hence, void. Otherwise, change to appropriate.
class LoginUseCase extends CompletableUseCase<LoginUseCaseParams> {
final AuthenticationRepository _authenticationRepository; // some dependency to be injected
// the functionality is hidden behind this
// abstract class defined in the Domain module
// It should be implemented inside the Data or Device
// module and passed polymorphically.

LoginUseCase(this._authenticationRepository);

@override
// Since the parameter type is void, `_` ignores the parameter. Change according to the type
// used in the template.
Future<Stream<void>> buildUseCaseStream(params) async {
final StreamController controller = StreamController();
try {
// assuming you pass credentials here
await _authenticationRepository.authenticate(email: params.email, password: params.password);
logger.finest('LoginUseCase successful.');
// triggers onComplete
controller.close();
} catch (e) {
print(e);
logger.severe('LoginUseCase unsuccessful.');
// Trigger .onError
controller.addError(e);
}
return controller.stream;
}
}

class LoginUseCaseParams {
final String email;
final String password;
LoginUseCaseParams(this.email, this.password);
}
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Background UseCase
A usecase can be made to run on a separate isolate using the BackgroundUseCase class.
Implementing this kind of usecase is a little different than a regular usecase due to the constraints of an isolate.
In order to create a BackgroundUseCase, simply extend the class and override the buildUseCaseTask method.
This method should return a UseCaseTask, which is just a function that has a void return type and takes a
BackgroundUseCaseParameters parameter. This method should be static and will contain all the code you wish to run
on a separate isolate. This method should communicate with the main isolate using the port provided in the BackgroundUseCaseParameters
as follows. This example is of a BackgroundUseCase that performs matrix multiplication.

class MatMulUseCase extends BackgroundUseCase<List<List<double>>, MatMulUseCaseParams> {

// must be overridden
@override
buildUseCaseTask() {
return matmul; // returns the static method that contains the code to be run on an isolate
}

/// This method will be executed on a separate isolate. The [params] contain all the data and the sendPort
/// needed
static void matmul(BackgroundUseCaseParams params) async {
MatMulUseCaseParams matMulParams = params.params as MatMulUseCaseParams;
List<List<double>> result = List<List<double>>.generate(
10, (i) => List<double>.generate(10, (j) => 0));

for (int i = 0; i < matMulParams.mat1.length; i++) {
for (int j = 0; j < matMulParams.mat1.length; j++) {
for (int k = 0; k < matMulParams.mat1.length; k++) {
result[i][j] += matMulParams.mat1[i][k] * matMulParams.mat2[k][j];
}
}
}
// send the result back to the main isolate
// this will be forwarded to the observer listneres
params.port.send(BackgroundUseCaseMessage(data: result));

}
}
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Just like a regular [UseCase], a parameter class is recommended for any [BackgroundUseCase].
An example corresponding to the above example would be
class MatMulUseCaseParams {
List<List<double>> mat1;
List<List<double>> mat2;
MatMulUseCaseParams(this.mat1, this.mat2);
MatMulUseCaseParams.random() {
var size = 10;
mat1 = List<List<double>>.generate(size,
(i) => List<double>.generate(size, (j) => i.toDouble() * size + j));

mat2 = List<List<double>>.generate(size,
(i) => List<double>.generate(size, (j) => i.toDouble() * size + j));
}
}
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Repository in Domain

abstract class AuthenticationRepository {
Future<void> register(
{@required String firstName,
@required String lastName,
@required String email,
@required String password});

/// Authenticates a user using his [username] and [password]
Future<void> authenticate(
{@required String email, @required String password});

/// Returns whether the [User] is authenticated.
Future<bool> isAuthenticated();

/// Returns the current authenticated [User].
Future<User> getCurrentUser();

/// Resets the password of a [User]
Future<void> forgotPassword(String email);

/// Logs out the [User]
Future<void> logout();
}

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This repository should be implemented in Data layer

class DataAuthenticationRepository extends AuthenticationRepository {
// singleton
static DataAuthenticationRepository _instance = DataAuthenticationRepository._internal();
DataAuthenticationRepository._internal();
factory DataAuthenticationRepository() => _instance;

@override
Future<void> register(
{@required String firstName,
@required String lastName,
@required String email,
@required String password}) {
// TODO: implement
}

/// Authenticates a user using his [username] and [password]
@override
Future<void> authenticate(
{@required String email, @required String password}) {
// TODO: implement
}

/// Returns whether the [User] is authenticated.
@override
Future<bool> isAuthenticated() {
// TODO: implement
}

/// Returns the current authenticated [User].
@override
Future<User> getCurrentUser() {
// TODO: implement
}

/// Resets the password of a [User]
@override
Future<void> forgotPassword(String email) {
// TODO: implement
}

/// Logs out the [User]
@override
Future<void> logout() {
// TODO: implement
}
}
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If the repository is platform-related, implement it in the Device layer.
Entity
Defined in Domain layer.

class User {
final String name;
final String email;
final String uid;
User(this.name, this.email, this.uid);
}

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Checkout a small example here and a full application built here.
Authors #
Shady Boukhary
Rafael Monteiro