Understanding Different Flutter Architectural Patterns

Flutter, Google’s UI toolkit, has gained immense popularity for its ability to build natively compiled applications for mobile, web, and desktop from a single codebase. The flexibility and richness of Flutter make it suitable for a wide range of applications. However, to ensure maintainability, scalability, and testability, adopting a robust architectural pattern is essential. In this blog post, we’ll delve into various architectural patterns commonly used in Flutter development, explaining their strengths, weaknesses, and implementation strategies.

Why Use Architectural Patterns in Flutter?

Architectural patterns provide a structured approach to organizing your code. They offer numerous benefits, including:

  • Maintainability: Well-organized code is easier to understand, modify, and maintain over time.
  • Testability: Decoupled components can be tested in isolation, ensuring reliability.
  • Scalability: Makes it easier to add new features and scale the application without introducing chaos.
  • Code Reusability: Allows for the reuse of components and logic across the application.
  • Collaboration: Simplifies collaboration among developers by providing a shared understanding of the codebase.

Common Flutter Architectural Patterns

Here are some of the most common architectural patterns used in Flutter development:

1. Model-View-Controller (MVC)

MVC is one of the oldest and most widely used architectural patterns. It divides an application into three interconnected parts:

  • Model: Manages the data and business logic. It notifies the view of any changes.
  • View: Displays the data to the user and allows interaction. It observes the model and updates itself when the model changes.
  • Controller: Handles user input and updates the model accordingly.
Pros of MVC
  • Simplicity: Easy to understand and implement.
  • Separation of Concerns: Clear separation of UI, logic, and data.
Cons of MVC
  • Tight Coupling: Can lead to complex dependencies between the components, making it hard to scale.
  • Not Ideal for Complex UIs: Can be difficult to manage with complex UIs due to frequent updates and interactions.
Example in Flutter

Though not the most common choice in Flutter due to the unidirectional data flow limitations, you can structure a Flutter app using MVC concepts. For example:


// Model
class UserModel {
  String name;
  String email;

  UserModel({required this.name, required this.email});
}

// View
import 'package:flutter/material.dart';
import 'package:mvc_pattern/mvc_pattern.dart';

import 'controller.dart';

class UserView extends StatefulWidget {
  @override
  UserState createState() => UserState();
}

class UserState extends StateMVC {
  UserState() : super(UserController());

  UserController get con => controller as UserController;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('User Details')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text('Name: ${con.user.name}'),
            Text('Email: ${con.user.email}'),
            ElevatedButton(
              onPressed: () => con.updateUser('Jane Doe', 'jane.doe@example.com'),
              child: const Text('Update User'),
            ),
          ],
        ),
      ),
    );
  }
}


// Controller
import 'package:mvc_pattern/mvc_pattern.dart';
import 'model.dart';

class UserController extends ControllerMVC {
  static late UserController _this;
  factory UserController() {
    if (_this == null) _this = UserController._();
    return _this;
  }
  UserController._() {
    user = UserModel(name: 'John Doe', email: 'john.doe@example.com');
  }

  UserModel user = UserModel(name: '', email: '');

  void updateUser(String name, String email) {
    user.name = name;
    user.email = email;
    update(); // Refreshes the view
  }
}

2. Model-View-Presenter (MVP)

MVP is an evolution of MVC designed to improve testability and separation of concerns. In MVP:

  • Model: Similar to MVC, it manages data and business logic.
  • View: An interface that the view implements. It passively displays data and forwards user actions to the presenter.
  • Presenter: Acts as an intermediary between the view and the model. It retrieves data from the model and formats it for display in the view.
Pros of MVP
  • Improved Testability: The presenter can be easily unit tested without the view.
  • Clear Separation of Concerns: Enhanced decoupling compared to MVC.
Cons of MVP
  • Increased Complexity: More classes and interfaces compared to MVC.
  • View Interface Definition: Requires defining interfaces for the view, adding to the boilerplate.
Example in Flutter

// Model
class UserModel {
  String name;
  String email;

  UserModel({required this.name, required this.email});
}

// View Interface
abstract class UserView {
  void displayUser(String name, String email);
}

// Presenter
class UserPresenter {
  UserView _view;
  UserModel _user;

  UserPresenter(this._view, this._user);

  void loadUser() {
    _view.displayUser(_user.name, _user.email);
  }

  void updateUser(String name, String email) {
    _user.name = name;
    _user.email = email;
    _view.displayUser(_user.name, _user.email);
  }
}

// View
import 'package:flutter/material.dart';

import 'presenter.dart';
import 'model.dart';

class UserPage extends StatefulWidget implements UserView {
  @override
  _UserPageState createState() => _UserPageState();

  @override
  void displayUser(String name, String email) {
     // Implementation handled in setState of _UserPageState
  }
}

class _UserPageState extends State {
  String _name = '';
  String _email = '';
  late UserPresenter _presenter;

  @override
  void initState() {
    super.initState();
    UserModel user = UserModel(name: 'John Doe', email: 'john.doe@example.com');
    _presenter = UserPresenter(widget, user);
    _presenter.loadUser();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('User Details')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text('Name: $_name'),
            Text('Email: $_email'),
            ElevatedButton(
              onPressed: () {
                _presenter.updateUser('Jane Doe', 'jane.doe@example.com');
              },
              child: const Text('Update User'),
            ),
          ],
        ),
      ),
    );
  }

   @override
  void displayUser(String name, String email) {
    setState(() {
      _name = name;
      _email = email;
    });
  }
}

3. Model-View-ViewModel (MVVM)

MVVM is an architectural pattern that facilitates a clear separation between the UI (View) and the data (Model) by introducing a ViewModel.

  • Model: Manages the application data.
  • View: Displays the data and allows users to interact with it. It is typically passive and binds to the ViewModel.
  • ViewModel: Exposes data relevant to the View. It retrieves data from the Model and formats it for the View to display.
Pros of MVVM
  • Enhanced Testability: ViewModel is easily testable without the View.
  • Clear Separation of Concerns: Better decoupling between the UI and the business logic.
  • Code Reusability: ViewModel can be reused across multiple views.
Cons of MVVM
  • Complexity: More complex than MVC, with additional classes and bindings.
  • Learning Curve: Requires a good understanding of data binding and reactive programming.
Example in Flutter

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

// Model
class UserModel {
  String name;
  String email;

  UserModel({required this.name, required this.email});
}

// ViewModel
class UserViewModel with ChangeNotifier {
  UserModel _user = UserModel(name: 'John Doe', email: 'john.doe@example.com');

  UserModel get user => _user;

  void updateUser(String name, String email) {
    _user = UserModel(name: name, email: email);
    notifyListeners(); // Notifies the listeners about the change
  }
}

// View
class UserView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final userViewModel = Provider.of(context);

    return Scaffold(
      appBar: AppBar(title: const Text('User Details')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text('Name: ${userViewModel.user.name}'),
            Text('Email: ${userViewModel.user.email}'),
            ElevatedButton(
              onPressed: () {
                userViewModel.updateUser('Jane Doe', 'jane.doe@example.com');
              },
              child: const Text('Update User'),
            ),
          ],
        ),
      ),
    );
  }
}

void main() {
  runApp(
    ChangeNotifierProvider(
      create: (context) => UserViewModel(),
      child: MaterialApp(
        home: UserView(),
      ),
    ),
  );
}

Explanation:

  • We use the provider package to manage and provide the UserViewModel.
  • The UserView is a StatelessWidget that obtains the UserViewModel using Provider.of.
  • When the updateUser function is called in the ViewModel, notifyListeners() is invoked, triggering a UI update.

4. Business Logic Component (BLoC)

BLoC is an architectural pattern introduced by Google specifically for Flutter. It focuses on managing state in a reactive manner using streams. BLoC consists of:

  • Events: Inputs to the BLoC from the UI or other parts of the application.
  • BLoC: Processes incoming events and emits state changes.
  • State: Represents the different states of the UI.
Pros of BLoC
  • State Management: Excellent for managing complex application state.
  • Testability: Easier to test business logic in isolation.
  • Reactivity: Integrates well with reactive programming paradigms.
Cons of BLoC
  • Boilerplate: Can require a significant amount of boilerplate code, especially for simple features.
  • Learning Curve: Steeper learning curve for developers not familiar with reactive programming.
Example in Flutter

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:equatable/equatable.dart';

// Events
abstract class UserEvent extends Equatable {
  @override
  List get props => [];
}

class LoadUser extends UserEvent {}

class UpdateUser extends UserEvent {
  final String name;
  final String email;

  UpdateUser({required this.name, required this.email});

  @override
  List get props => [name, email];
}


// State
class UserState extends Equatable {
  final String name;
  final String email;

  UserState({required this.name, required this.email});

  @override
  List get props => [name, email];
}

class UserInitial extends UserState {
  UserInitial() : super(name: 'Initial Name', email: 'initial@example.com');
}


// BLoC
class UserBloc extends Bloc {
  UserBloc() : super(UserInitial()) {
    on((event, emit) {
      // Load initial user data if needed
      emit(UserState(name: 'John Doe', email: 'john.doe@example.com'));
    });

    on((event, emit) {
      emit(UserState(name: event.name, email: event.email));
    });
  }
}


// View
class UserView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocProvider(
      create: (context) => UserBloc()..add(LoadUser()),
      child: Scaffold(
        appBar: AppBar(title: const Text('User Details')),
        body: Center(
          child: BlocBuilder(
            builder: (context, state) {
              return Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  Text('Name: ${state.name}'),
                  Text('Email: ${state.email}'),
                  ElevatedButton(
                    onPressed: () {
                      BlocProvider.of(context).add(
                        UpdateUser(name: 'Jane Doe', email: 'jane.doe@example.com'),
                      );
                    },
                    child: const Text('Update User'),
                  ),
                ],
              );
            },
          ),
        ),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(home: UserView()));
}


Explanation:


    

  • We use the flutter_bloc package for BLoC implementation and equatable for state comparison.
    • 

  • Events are defined for loading and updating user information.
    • 

  • The BLoC handles these events and emits different states accordingly.
    • 

  • The UI (UserView) listens for state changes and updates the UI accordingly.
    • 



5. Redux


Redux is a predictable state container for JavaScript apps, which can also be used in Flutter via packages like flutter_redux. Redux revolves around a single store, actions, and reducers:


    

  • Store: Holds the entire application state in a single immutable object.
    • 

  • Actions: Describe the intention to change the state.
    • 

  • Reducers: Pure functions that specify how the state changes in response to actions.
    • 



Pros of Redux


    

  • Centralized State: Manages application state in a predictable manner.
    • 

  • Debugging: Makes debugging easier due to the immutability and predictability of the state.
    • 

  • Middleware: Supports middleware for handling side effects.
    • 



Cons of Redux


    

  • Boilerplate: Requires significant boilerplate code.
    • 

  • Complexity: Can be overkill for small and simple applications.
    • 



Example in Flutter



import 'package:flutter/material.dart';
import 'package:flutter_redux/flutter_redux.dart';
import 'package:redux/redux.dart';

// State
class AppState {
  final String name;
  final String email;

  AppState({required this.name, required this.email});

  // Creates a new AppState object with updated fields
  AppState copyWith({String? name, String? email}) {
    return AppState(
      name: name ?? this.name, // Use the new name if provided, otherwise use the existing name
      email: email ?? this.email, // Use the new email if provided, otherwise use the existing email
    );
  }
}

// Actions
class UpdateUserAction {
  final String name;
  final String email;

  UpdateUserAction({required this.name, required this.email});
}


// Reducer
AppState reducer(AppState state, dynamic action) {
  if (action is UpdateUserAction) {
    return state.copyWith(name: action.name, email: action.email);
  }
  return state;
}

// View
class UserView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StoreConnector(
      converter: (store) => ViewModel.fromStore(store),
      builder: (context, viewModel) {
        return Scaffold(
          appBar: AppBar(title: const Text('User Details')),
          body: Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                Text('Name: ${viewModel.name}'),
                Text('Email: ${viewModel.email}'),
                ElevatedButton(
                  onPressed: () {
                    viewModel.onUpdateUser('Jane Doe', 'jane.doe@example.com');
                  },
                  child: const Text('Update User'),
                ),
              ],
            ),
          ),
        );
      },
    );
  }
}

class ViewModel {
  final String name;
  final String email;
  final Function(String, String) onUpdateUser;

  ViewModel({
    required this.name,
    required this.email,
    required this.onUpdateUser,
  });

  static fromStore(Store store) {
    return ViewModel(
      name: store.state.name,
      email: store.state.email,
      onUpdateUser: (name, email) {
        store.dispatch(UpdateUserAction(name: name, email: email));
      },
    );
  }
}

void main() {
  final store = Store(
    reducer,
    initialState: AppState(name: 'John Doe', email: 'john.doe@example.com'),
  );

  runApp(
    MaterialApp(
      home: StoreProvider(
        store: store,
        child: UserView(),
      ),
    ),
  );
}



6. Provider Pattern


The Provider pattern, often used with Flutter, is a form of dependency injection and state management made easy by the Provider package. It is lightweight, easy to understand, and fits well with Flutter’s reactive nature. It does not enforce a strict architectural pattern but helps in managing state efficiently by providing an easy way to access the data throughout the widget tree.


Pros of Provider


    

  • Simple and Lightweight: Easy to set up and use.
    • 

  • Centralized State: Manages application state efficiently.
    • 

  • Reactivity: Facilitates efficient rebuilding of UI when data changes.
    • 



Cons of Provider


    

  • Lesser Structure: No explicit structural requirements; can result in unstructured code without strict organization.
    • 

  • State Management Limitations: May be less powerful than BLoC or Redux for large and complex applications.
    • 



Example in Flutter



import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

// Model
class UserModel {
  String name;
  String email;

  UserModel({required this.name, required this.email});
}

// Provider/ViewModel
class UserProvider with ChangeNotifier {
  UserModel _user = UserModel(name: 'John Doe', email: 'john.doe@example.com');

  UserModel get user => _user;

  void updateUser(String name, String email) {
    _user = UserModel(name: name, email: email);
    notifyListeners(); // Notifies listeners to rebuild dependent widgets
  }
}

// View
class UserView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final userProvider = Provider.of(context);

    return Scaffold(
      appBar: AppBar(title: const Text('User Details')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text('Name: ${userProvider.user.name}'),
            Text('Email: ${userProvider.user.email}'),
            ElevatedButton(
              onPressed: () {
                userProvider.updateUser('Jane Doe', 'jane.doe@example.com');
              },
              child: const Text('Update User'),
            ),
          ],
        ),
      ),
    );
  }
}

void main() {
  runApp(
    ChangeNotifierProvider(
      create: (context) => UserProvider(),
      child: MaterialApp(
        home: UserView(),
      ),
    ),
  );
}



Choosing the Right Architectural Pattern


Selecting the appropriate architectural pattern depends on several factors:


    

  • Project Size: For small projects, MVC or Provider may suffice. Larger, complex projects may benefit from MVVM, BLoC, or Redux.
    • 

  • Team Experience: Choose a pattern that aligns with the team’s expertise and familiarity.
    • 

  • Complexity: Consider the complexity of state management. BLoC and Redux are well-suited for applications with intricate state requirements.
    • 

  • Testability: If testability is a high priority, MVVM, MVP, and BLoC offer advantages.
    • 



Conclusion


Understanding and adopting a suitable architectural pattern is crucial for developing scalable, maintainable, and testable Flutter applications. While MVC, MVP, MVVM, BLoC, Redux, and the Provider pattern all have their strengths and weaknesses, choosing the right pattern depends on the specific requirements of your project and your team’s preferences. By carefully evaluating these factors, you can ensure that your Flutter app is well-structured and can evolve gracefully over time.


Beyond This Article: Your Next Discovery Awaits
Improving the Overall Maintainability and Readability of Your Flutter Codebase
Using the BLoC (Business Logic Component) or Cubit Pattern for State Management and Architecture in Flutter
Understanding the Architecture and Platform Differences for Flutter Desktop Apps
Understanding Flutter Desktop Architecture
Exploring Different Architectural Patterns (MVVM, MVP, Clean Architecture) in Flutter
Implementing Various Data Caching Strategies (In-Memory, Disk-Based) in Flutter
	


		
	
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