flutter-architecting-apps

Architecting Flutter Applications

Contents

• Core Architectural Principles
• Structuring the Layers
• Implementing the Data Layer
• Feature Implementation Workflow
• Examples

Core Architectural Principles

Design Flutter applications to scale by strictly adhering to the following principles:

• Enforce Separation of Concerns: Decouple UI rendering from business logic and data fetching. Organize the codebase into distinct layers (UI, Logic, Data) and further separate by feature within those layers.
• Maintain a Single Source of Truth (SSOT): Centralize application state and data in the Data layer. Ensure the SSOT is the only component authorized to mutate its respective data.
• Implement Unidirectional Data Flow (UDF): Flow state downwards from the Data layer to the UI layer. Flow events upwards from the UI layer to the Data layer.
• Treat UI as a Function of State: Drive the UI entirely via immutable state objects. Rebuild widgets reactively when the underlying state changes.

Structuring the Layers

Separate the application into 2 to 3 distinct layers depending on complexity. Restrict communication so that a layer only interacts with the layer directly adjacent to it.

1. UI Layer (Presentation)

• Views (Widgets): Build reusable, lean widgets. Strip all business and data-fetching logic from the widget tree. Restrict widget logic to UI-specific concerns (e.g., animations, routing, layout constraints).
• ViewModels: Manage the UI state. Consume domain models from the Data/Logic layers and transform them into presentation-friendly formats. Expose state to the Views and handle user interaction events.

2. Logic Layer (Domain) - Conditional

• If the application requires complex client-side business logic: Implement a Logic layer containing Use Cases or Interactors. Use this layer to orchestrate interactions between multiple repositories before passing data to the UI layer.
• If the application is a standard CRUD app: Omit this layer. Allow ViewModels to interact directly with Repositories.