Flutter App Example

Overview

This example demonstrates a complete Flutter application built with Nest Dart, featuring:

Modular architecture with dependency injection
Route management with go_router integration
Service-based architecture for API calls
State management with Provider
Multiple modules with shared dependencies

Project Structure

flutter_app/
├── lib/
│   ├── main.dart                 # App entry point
│   ├── models/
│   │   └── todo.dart            # Todo data model
│   ├── modules/
│   │   ├── core_module.dart     # Core services module
│   │   ├── splash_module.dart   # Splash screen module
│   │   └── todo_module.dart     # Todo feature module
│   ├── providers/
│   │   └── todo_provider.dart   # State management
│   ├── services/
│   │   └── todo_service.dart    # API service
│   ├── utils/
│   │   ├── config_preference.dart
│   │   └── preference_keys.dart
│   └── views/
│       ├── todo_list_view.dart  # Todo list screen
│       └── todo_detail_view.dart # Todo detail screen
└── pubspec.yaml

Getting Started

Install Dependencies

Navigate to the example directory and install dependencies:

cd examples/flutter_app
flutter pub get

Run the Application

Launch the app on your connected device or emulator:

flutter run

Explore Features

The app will launch with a todo list that:

Fetches todos from JSONPlaceholder API
Displays them in a scrollable list
Allows navigation to individual todo details
Supports pull-to-refresh

Module Organization

App Module

The root module imports all feature modules and initializes the app:

lib/main.dart

import 'package:flutter/material.dart';
import 'package:flutter_app/modules/splash_module.dart';
import 'package:flutter_app/modules/todo_module.dart';
import 'package:nest_flutter/nest_flutter.dart';
import 'package:provider/provider.dart' hide Locator;
import 'package:go_router/go_router.dart';
import 'providers/todo_provider.dart';

class AppModule extends Module {
  @override
  List<Module> get imports => [
    SplashModule(),
    TodoModule(),
    ModuleA(),
    ModuleB(),
  ];

  @override
  Future<void> providers(Locator _) async {}
}

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(ModularApp(module: AppModule(), child: const MainApp()));
}

Core Module

Provides shared services across the application:

lib/modules/core_module.dart

import 'package:flutter_app/utils/config_preference.dart';
import 'package:nest_flutter/nest_flutter.dart';
import 'package:http/http.dart';
import 'package:shared_preferences/shared_preferences.dart';

class CoreModule extends Module {
  @override
  Future<void> providers(Locator locator) async {
    locator.registerSingleton<Client>(Client());
    final prefs = await SharedPreferences.getInstance();
    locator.registerSingleton<SharedPreferences>(prefs);
    locator.registerSingleton<ConfigPreference>(ConfigPreference(prefs));
  }

  @override
  List<Type> get exports => [Client, SharedPreferences, ConfigPreference];
}

The exports property makes these services available to other modules that import CoreModule.

Todo Module

Encapsulates the todo feature with routes, services, and providers:

lib/modules/todo_module.dart

import 'package:flutter/widgets.dart';
import 'package:flutter_app/modules/core_module.dart';
import 'package:flutter_app/services/todo_service.dart';
import 'package:flutter_app/providers/todo_provider.dart';
import 'package:flutter_app/utils/config_preference.dart';
import 'package:flutter_app/views/todo_list_view.dart';
import 'package:flutter_app/views/todo_detail_view.dart';
import 'package:nest_flutter/nest_flutter.dart';
import 'package:http/http.dart';

class TodoModule extends Module {
  @override
  List<Module> get imports => [CoreModule()];

  @override
  Future<void> providers(Locator locator) async {
    locator.registerSingleton<TodoService>(
      JsonPlaceholderTodoService(client: locator.get<Client>()),
    );
    locator.registerSingleton<TodoProvider>(
      TodoProvider(locator.get<TodoService>(), locator.get<ConfigPreference>()),
    );
  }

  @override
  List<Type> get exports => [TodoService, TodoProvider];

  @override
  String? get routePrefix => '/todos';

  @override
  List<RouteBase> get routes => [
    GoRoute(path: '/', builder: (context, state) => const TodoListView()),
    GoRoute(
      path: '/:id',
      builder: (context, state) => TodoDetailView(
        todoId: int.tryParse(state.pathParameters['id'] ?? '0') ?? 0,
      ),
    ),
  ];
}

Route Setup

Nest Flutter integrates seamlessly with go_router:

lib/main.dart

class MainApp extends StatelessWidget {
  const MainApp({super.key});

  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (context) => Modular.get<TodoProvider>(),
      child: MaterialApp.router(
        routerConfig: Modular.router((router) {
          return GoRouter(
            routes: router.configuration.routes,
            initialLocation: '/todos',
            debugLogDiagnostics: true,
          );
        }),
      ),
    );
  }
}

Key Points

Modular.router() collects routes from all modules
Each module can define a routePrefix for its routes
Routes automatically inherit the module’s prefix
Full go_router features available (parameters, guards, etc.)

Service Implementation

The TodoService demonstrates dependency injection and API integration:

lib/services/todo_service.dart

import 'dart:convert';
import 'package:http/http.dart' as http;
import '../models/todo.dart';

abstract class TodoService {
  Future<List<Todo>> getAllTodos();
  Future<Todo> getTodoById(int id);
}

class JsonPlaceholderTodoService implements TodoService {
  static const String _baseUrl = 'https://jsonplaceholder.typicode.com';
  final http.Client _client;

  JsonPlaceholderTodoService({http.Client? client})
    : _client = client ?? http.Client();

  @override
  Future<List<Todo>> getAllTodos() async {
    await Future.delayed(const Duration(seconds: 2));
    try {
      final response = await _client.get(
        Uri.parse('$_baseUrl/todos'),
        headers: {'Content-Type': 'application/json'},
      );

      if (response.statusCode == 200) {
        final List<dynamic> jsonList = json.decode(response.body);
        return jsonList.map((json) => Todo.fromJson(json)).toList();
      } else {
        throw TodoServiceException(
          'Failed to load todos: ${response.statusCode}',
          response.statusCode,
        );
      }
    } catch (e) {
      if (e is TodoServiceException) rethrow;
      throw TodoServiceException('Network error: $e');
    }
  }

  @override
  Future<Todo> getTodoById(int id) async {
    try {
      final response = await _client.get(
        Uri.parse('$_baseUrl/todos/$id'),
        headers: {'Content-Type': 'application/json'},
      );

      if (response.statusCode == 200) {
        final Map<String, dynamic> jsonMap = json.decode(response.body);
        return Todo.fromJson(jsonMap);
      } else if (response.statusCode == 404) {
        throw TodoServiceException('Todo with ID $id not found', 404);
      } else {
        throw TodoServiceException(
          'Failed to load todo: ${response.statusCode}',
          response.statusCode,
        );
      }
    } catch (e) {
      if (e is TodoServiceException) rethrow;
      throw TodoServiceException('Network error: $e');
    }
  }
}

class TodoServiceException implements Exception {
  final String message;
  final int? statusCode;

  TodoServiceException(this.message, [this.statusCode]);

  @override
  String toString() => 'TodoServiceException: $message';
}

Using Services in Widgets

Services are accessed through the Provider pattern:

lib/views/todo_list_view.dart

import 'package:flutter/material.dart';
import 'package:go_router/go_router.dart';
import 'package:provider/provider.dart';
import '../models/todo.dart';
import '../providers/todo_provider.dart';

class TodoListView extends StatefulWidget {
  const TodoListView({super.key});

  @override
  State<TodoListView> createState() => _TodoListViewState();
}

class _TodoListViewState extends State<TodoListView> {
  @override
  void initState() {
    super.initState();
    // Load todos when the widget initializes
    WidgetsBinding.instance.addPostFrameCallback((_) {
      context.read<TodoProvider>().loadTodos();
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Todos'),
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        actions: [
          Consumer<TodoProvider>(
            builder: (context, todoProvider, child) {
              return IconButton(
                icon: const Icon(Icons.refresh),
                onPressed: todoProvider.isLoading
                    ? null
                    : () => todoProvider.refreshTodos(),
              );
            },
          ),
        ],
      ),
      body: Consumer<TodoProvider>(
        builder: (context, todoProvider, child) {
          return _buildBody(todoProvider);
        },
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => _showTodoByIdDialog(),
        tooltip: 'View Todo by ID',
        child: const Icon(Icons.search),
      ),
    );
  }

  Widget _buildBody(TodoProvider todoProvider) {
    if (todoProvider.isLoading) {
      return const Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            CircularProgressIndicator(),
            SizedBox(height: 16),
            Text('Loading todos...'),
          ],
        ),
      );
    }

    if (todoProvider.error != null) {
      return Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Icon(Icons.error_outline, size: 64, color: Colors.red),
            const SizedBox(height: 16),
            Text(
              'Error loading todos',
              style: Theme.of(context).textTheme.headlineSmall,
            ),
            const SizedBox(height: 8),
            Text(
              todoProvider.error!,
              textAlign: TextAlign.center,
              style: Theme.of(context).textTheme.bodyMedium,
            ),
            const SizedBox(height: 16),
            ElevatedButton(
              onPressed: () => todoProvider.refreshTodos(),
              child: const Text('Retry'),
            ),
          ],
        ),
      );
    }

    return RefreshIndicator(
      onRefresh: () => todoProvider.refreshTodos(),
      child: ListView.builder(
        itemCount: todoProvider.todos.length,
        itemBuilder: (context, index) {
          final todo = todoProvider.todos[index];
          return _buildTodoTile(todo);
        },
      ),
    );
  }

  Widget _buildTodoTile(Todo todo) {
    return Card(
      margin: const EdgeInsets.symmetric(horizontal: 16, vertical: 4),
      child: ListTile(
        leading: CircleAvatar(
          backgroundColor: todo.completed ? Colors.green : Colors.orange,
          child: Text(
            todo.id.toString(),
            style: const TextStyle(
              color: Colors.white,
              fontWeight: FontWeight.bold,
            ),
          ),
        ),
        title: Text(
          todo.title,
          style: TextStyle(
            decoration: todo.completed ? TextDecoration.lineThrough : null,
            color: todo.completed ? Colors.grey : null,
          ),
        ),
        subtitle: Text('User ID: ${todo.userId}'),
        trailing: Icon(
          todo.completed ? Icons.check_circle : Icons.radio_button_unchecked,
          color: todo.completed ? Colors.green : Colors.grey,
        ),
        onTap: () => context.push('/todos/${todo.id}'),
      ),
    );
  }
}

Data Model

The Todo model with JSON serialization:

lib/models/todo.dart

class Todo {
  final int id;
  final int userId;
  final String title;
  final bool completed;

  const Todo({
    required this.id,
    required this.userId,
    required this.title,
    required this.completed,
  });

  factory Todo.fromJson(Map<String, dynamic> json) {
    return Todo(
      id: json['id'] as int,
      userId: json['userId'] as int,
      title: json['title'] as String,
      completed: json['completed'] as bool,
    );
  }

  Map<String, dynamic> toJson() {
    return {
      'id': id,
      'userId': userId,
      'title': title,
      'completed': completed
    };
  }
}

Key Concepts Demonstrated

Dependency Injection

Services are registered in modules and injected where needed, making testing and maintenance easier.

Module Imports

TodoModule imports CoreModule to access shared services like HTTP client and preferences.

Route Prefixes

Each module defines its own route prefix, creating clean URL structure automatically.

Service Abstraction

Abstract TodoService allows easy swapping of implementations for testing or different backends.

Next Steps

Explore the Module System for advanced patterns
Learn about Dependency Injection
Check out the Frog Backend Example for a complete backend
See Flutter Integration for more Flutter-specific features

​Overview

​Project Structure

​Getting Started

​Module Organization

​App Module

​Core Module

​Todo Module

​Route Setup

Key Points

​Service Implementation

​Using Services in Widgets

​Data Model

​Key Concepts Demonstrated

Dependency Injection

Module Imports

Route Prefixes

Service Abstraction

​Next Steps

Overview

Project Structure

Getting Started

Module Organization

App Module

Core Module

Todo Module

Route Setup

Service Implementation

Using Services in Widgets

Data Model

Key Concepts Demonstrated

Next Steps