flutter-architecture

Flutter App Architecture Implementation

Goal

Implement a scalable, maintainable Flutter application architecture using the MVVM pattern, unidirectional data flow, and strict separation of concerns across UI, Domain, and Data layers. Use provider for dependency injection and ListenableBuilder for reactive UI updates.

Decision Logic

Before implementing a feature, evaluate the architectural requirements using the following logic:

1. Data Source:
   • If interacting with an external API -> Create a Remote Service.
   • If interacting with local storage (SQL/Key-Value) -> Create a Local Service.
2. Business Logic Complexity:
   • If the feature requires merging data from multiple repositories or contains highly complex, reusable logic -> Implement a Domain Layer (UseCases).
   • If the feature is standard CRUD or simple data presentation -> Skip the Domain Layer; the ViewModel communicates directly with the Repository.

Instructions

1. Analyze Feature Requirements Evaluate the requested feature to determine the necessary data models, services, and UI state. STOP AND ASK THE USER: "Please provide the specific data models, API endpoints, or local storage requirements for this feature, and confirm if complex business logic requires a dedicated Domain (UseCase) layer."

2. Implement the Data Layer: Services Create a stateless service class to wrap the external API or local storage. This class must not contain business logic or state.

   class SharedPreferencesService {
     static const String _kDarkMode = 'darkMode';
   
     Future<void> setDarkMode(bool value) async {
       final prefs = await SharedPreferences.getInstance();
       await prefs.setBool(_kDarkMode, value);
     }
   
     Future<bool> isDarkMode() async {
       final prefs = await SharedPreferences.getInstance();
       return prefs.getBool(_kDarkMode) ?? false;
     }
   }
   

3. Implement the Data Layer: Repositories Create a repository to act as the single source of truth. The repository consumes the service, handles errors using Result objects (see the Result and Command Reference Guide), and exposes domain models or streams.