Flutter Architecture

Flutter Architecture

Overview

Provides architectural guidance and best practices for building scalable Flutter applications using MVVM pattern, layered architecture, and recommended design patterns from the Flutter team.

Project Structure: Feature-First vs Layer-First

Choose the right project organization based on your app's complexity and team size.

Feature-First (Recommended for teams)

Organize code by business features:

lib/
├── features/
│   ├── auth/
│   │   ├── data/
│   │   ├── domain/
│   │   └── presentation/
│   ├── todos/
│   │   ├── data/
│   │   ├── domain/
│   │   └── presentation/
│   └── settings/
│       ├── data/
│       ├── domain/
│       └── presentation/
├── shared/
│   ├── core/
│   ├── data/
│   └── ui/
└── main.dart

When to use:

• Medium to large apps (10+ features)
• Team development (2+ developers)
• Frequently adding/removing features
• Complex business logic

Benefits:

• Features are self-contained units
• Easy to add/remove entire features
• Clear feature boundaries
• Reduced merge conflicts
• Teams work independently on features

See Feature-First Guide for complete implementation details.

Layer-First (Traditional)

Organize code by architectural layers:

lib/
├── data/
│   ├── repositories/
│   ├── services/
│   └── models/
├── domain/
│   ├── use-cases/
│   └── entities/
├── presentation/
│   ├── views/
│   └── viewmodels/
└── shared/

When to use:

• Small to medium apps
• Few features (<10)
• Solo developers or small teams
• Simple business logic

Benefits:

• Clear separation by layer
• Easy to find components by type
• Less nesting

Quick Start

Start with these core concepts:

1. Separation of concerns - Split app into UI and Data layers
2. MVVM pattern - Use Views, ViewModels, Repositories, and Services
3. Single source of truth - Repositories hold the authoritative data
4. Unidirectional data flow - State flows from data → logic → UI

For detailed concepts, see Concepts.

Architecture Layers

Flutter apps should be structured in layers:

• UI Layer: Views (widgets) and ViewModels (UI logic)
• Data Layer: Repositories (SSOT) and Services (data sources)
• Domain Layer (optional): Use-cases for complex business logic

See Layers Guide for detailed layer responsibilities and interactions.

Core Components

Views

• Compose widgets for UI presentation
• Contain minimal logic (animations, simple conditionals, routing)
• Receive data from ViewModels
• Pass events via ViewModel commands

ViewModels

• Transform repository data into UI state
• Manage UI state and commands
• Handle business logic for UI interactions
• Expose state as streams or change notifiers

Repositories

• Single source of truth for data types
• Aggregate data from services
• Handle caching, error handling, retry logic
• Expose data as domain models

Services

• Wrap external data sources (APIs, databases, platform APIs)
• Stateless data access layer
• One service per data source

Design Patterns

Common patterns for robust Flutter apps:

• Command Pattern - Encapsulate actions with Result handling
• Result Type - Type-safe error handling
• Repository Pattern - Abstraction over data sources
• Offline-First - Optimistic UI updates with sync

See Design Patterns for implementation details.

When to Use This Skill

Use this skill when:

• Designing or refactoring Flutter app architecture
• Choosing between feature-first and layer-first project structure
• Implementing MVVM pattern in Flutter
• Creating scalable app structure for teams
• Adding new features to existing architecture
• Applying best practices and design patterns

Resources

references/

• concepts.md - Core architectural principles (separation of concerns, SSOT, UDF)
• feature-first.md - Feature-first project organization and best practices
• mvvm.md - MVVM pattern implementation in Flutter
• layers.md - Detailed layer responsibilities and interactions
• design-patterns.md - Common patterns and implementations

assets/

• command.dart - Command pattern template for encapsulating actions
• result.dart - Result type for safe error handling
• examples/ - Code examples showing architecture in practice

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