Learn how to build scalable, testable Flutter apps using MVVM architecture.
Introduction: Why App Architecture Matters in Flutter
Introduction: Why App Architecture Matters in Flutter
Introduction: Why App Architecture Matters in Flutter
Introduction: Why App Architecture Matters in Flutter
As Flutter developers, we often start with excitement, dragging and dropping widgets to see UI take shape. But as the codebase grows, features multiply, and multiple developers jump in—things can quickly spiral into chaos. Bugs appear out of nowhere, adding a new feature feels like walking a tightrope, and testing becomes a nightmare.
That’s where app architecture comes in.
This blog takes you deep into Flutter’s recommended architectural model based on MVVM (Model-View-ViewModel). We'll explore all major layers—UI, Data, and optional Domain—and how they interact to keep your codebase clean, scalable, and test-friendly. This guide recommends you split your application into the following components:
Views
View models
Repositories
Services
As Flutter developers, we often start with excitement, dragging and dropping widgets to see UI take shape. But as the codebase grows, features multiply, and multiple developers jump in—things can quickly spiral into chaos. Bugs appear out of nowhere, adding a new feature feels like walking a tightrope, and testing becomes a nightmare.
That’s where app architecture comes in.
This blog takes you deep into Flutter’s recommended architectural model based on MVVM (Model-View-ViewModel). We'll explore all major layers—UI, Data, and optional Domain—and how they interact to keep your codebase clean, scalable, and test-friendly. This guide recommends you split your application into the following components:
Views
View models
Repositories
Services
As Flutter developers, we often start with excitement, dragging and dropping widgets to see UI take shape. But as the codebase grows, features multiply, and multiple developers jump in—things can quickly spiral into chaos. Bugs appear out of nowhere, adding a new feature feels like walking a tightrope, and testing becomes a nightmare.
That’s where app architecture comes in.
This blog takes you deep into Flutter’s recommended architectural model based on MVVM (Model-View-ViewModel). We'll explore all major layers—UI, Data, and optional Domain—and how they interact to keep your codebase clean, scalable, and test-friendly. This guide recommends you split your application into the following components:
Views
View models
Repositories
Services
As Flutter developers, we often start with excitement, dragging and dropping widgets to see UI take shape. But as the codebase grows, features multiply, and multiple developers jump in—things can quickly spiral into chaos. Bugs appear out of nowhere, adding a new feature feels like walking a tightrope, and testing becomes a nightmare.
That’s where app architecture comes in.
This blog takes you deep into Flutter’s recommended architectural model based on MVVM (Model-View-ViewModel). We'll explore all major layers—UI, Data, and optional Domain—and how they interact to keep your codebase clean, scalable, and test-friendly. This guide recommends you split your application into the following components:
Views
View models
Repositories
Services
What is Flutter App Architecture?
What is Flutter App Architecture?
What is Flutter App Architecture?
What is Flutter App Architecture?
Flutter app architecture is the structure and strategy you use to build, manage, and maintain your app’s code. A good architecture keeps features modular, logic isolated, and code readable. It separates responsibilities clearly so developers know exactly where things belong.
Flutter’s recommended model focuses on two primary layers:
UI Layer (Views + ViewModels)
Data Layer (Repositories + Services)
An optional third layer, called the Domain Layer, helps with complex business logic reuse.
The Importance of Separation of Concerns (SoC)
SoC is a fundamental software principle where each part of your application is responsible for a single concern. Flutter architecture enforces this by:
Assigning UI rendering to the View
Business logic to the ViewModel
Data access to Repositories and Services
This separation reduces bugs, simplifies testing, and keeps your code easy to extend.
Flutter app architecture is the structure and strategy you use to build, manage, and maintain your app’s code. A good architecture keeps features modular, logic isolated, and code readable. It separates responsibilities clearly so developers know exactly where things belong.
Flutter’s recommended model focuses on two primary layers:
UI Layer (Views + ViewModels)
Data Layer (Repositories + Services)
An optional third layer, called the Domain Layer, helps with complex business logic reuse.
The Importance of Separation of Concerns (SoC)
SoC is a fundamental software principle where each part of your application is responsible for a single concern. Flutter architecture enforces this by:
Assigning UI rendering to the View
Business logic to the ViewModel
Data access to Repositories and Services
This separation reduces bugs, simplifies testing, and keeps your code easy to extend.
Flutter app architecture is the structure and strategy you use to build, manage, and maintain your app’s code. A good architecture keeps features modular, logic isolated, and code readable. It separates responsibilities clearly so developers know exactly where things belong.
Flutter’s recommended model focuses on two primary layers:
UI Layer (Views + ViewModels)
Data Layer (Repositories + Services)
An optional third layer, called the Domain Layer, helps with complex business logic reuse.
The Importance of Separation of Concerns (SoC)
SoC is a fundamental software principle where each part of your application is responsible for a single concern. Flutter architecture enforces this by:
Assigning UI rendering to the View
Business logic to the ViewModel
Data access to Repositories and Services
This separation reduces bugs, simplifies testing, and keeps your code easy to extend.
Flutter app architecture is the structure and strategy you use to build, manage, and maintain your app’s code. A good architecture keeps features modular, logic isolated, and code readable. It separates responsibilities clearly so developers know exactly where things belong.
Flutter’s recommended model focuses on two primary layers:
UI Layer (Views + ViewModels)
Data Layer (Repositories + Services)
An optional third layer, called the Domain Layer, helps with complex business logic reuse.
The Importance of Separation of Concerns (SoC)
SoC is a fundamental software principle where each part of your application is responsible for a single concern. Flutter architecture enforces this by:
Assigning UI rendering to the View
Business logic to the ViewModel
Data access to Repositories and Services
This separation reduces bugs, simplifies testing, and keeps your code easy to extend.
Understanding the MVVM Design Pattern
Understanding the MVVM Design Pattern
Understanding the MVVM Design Pattern
Understanding the MVVM Design Pattern
MVVM (Model-View-ViewModel) is a proven pattern that works wonderfully in Flutter:
View: Renders the UI and receives user input.
ViewModel: Manages UI state, business logic, and commands.
Model: Represents the data layer (repositories and services).
This pattern encourages reusability, testability, and cleaner widget trees.
A single feature of an application might require all of the following objects:
Each of these objects and the arrows that connect them will be explained thoroughly by the end of this page. Throughout this guide, the following simplified version of that diagram will be used as an anchor.
MVVM (Model-View-ViewModel) is a proven pattern that works wonderfully in Flutter:
View: Renders the UI and receives user input.
ViewModel: Manages UI state, business logic, and commands.
Model: Represents the data layer (repositories and services).
This pattern encourages reusability, testability, and cleaner widget trees.
A single feature of an application might require all of the following objects:
Each of these objects and the arrows that connect them will be explained thoroughly by the end of this page. Throughout this guide, the following simplified version of that diagram will be used as an anchor.
MVVM (Model-View-ViewModel) is a proven pattern that works wonderfully in Flutter:
View: Renders the UI and receives user input.
ViewModel: Manages UI state, business logic, and commands.
Model: Represents the data layer (repositories and services).
This pattern encourages reusability, testability, and cleaner widget trees.
A single feature of an application might require all of the following objects:
Each of these objects and the arrows that connect them will be explained thoroughly by the end of this page. Throughout this guide, the following simplified version of that diagram will be used as an anchor.
MVVM (Model-View-ViewModel) is a proven pattern that works wonderfully in Flutter:
View: Renders the UI and receives user input.
ViewModel: Manages UI state, business logic, and commands.
Model: Represents the data layer (repositories and services).
This pattern encourages reusability, testability, and cleaner widget trees.
A single feature of an application might require all of the following objects:
Each of these objects and the arrows that connect them will be explained thoroughly by the end of this page. Throughout this guide, the following simplified version of that diagram will be used as an anchor.
UI Layer – Views & ViewModels
UI Layer – Views & ViewModels
UI Layer – Views & ViewModels
UI Layer – Views & ViewModels
The UI layer handles what the user sees and does. Views display information. ViewModels process logic and control the UI’s behavior.
Full Explanation:
Views: These are your Flutter widgets. They should contain little to no logic. Their only responsibility is to present the UI and pass user input to the ViewModel.
ViewModels:
Transform raw data from the repository into UI-ready state.
Maintain flags (loading, error, visibility, etc.).
Expose callback functions (commands) to the View for interactions.
Relationship: Views and ViewModels work in 1:1 pairs per feature. Example: LoginView ↔ LoginViewModel.
The UI layer handles what the user sees and does. Views display information. ViewModels process logic and control the UI’s behavior.
Full Explanation:
Views: These are your Flutter widgets. They should contain little to no logic. Their only responsibility is to present the UI and pass user input to the ViewModel.
ViewModels:
Transform raw data from the repository into UI-ready state.
Maintain flags (loading, error, visibility, etc.).
Expose callback functions (commands) to the View for interactions.
Relationship: Views and ViewModels work in 1:1 pairs per feature. Example: LoginView ↔ LoginViewModel.
The UI layer handles what the user sees and does. Views display information. ViewModels process logic and control the UI’s behavior.
Full Explanation:
Views: These are your Flutter widgets. They should contain little to no logic. Their only responsibility is to present the UI and pass user input to the ViewModel.
ViewModels:
Transform raw data from the repository into UI-ready state.
Maintain flags (loading, error, visibility, etc.).
Expose callback functions (commands) to the View for interactions.
Relationship: Views and ViewModels work in 1:1 pairs per feature. Example: LoginView ↔ LoginViewModel.
The UI layer handles what the user sees and does. Views display information. ViewModels process logic and control the UI’s behavior.
Full Explanation:
Views: These are your Flutter widgets. They should contain little to no logic. Their only responsibility is to present the UI and pass user input to the ViewModel.
ViewModels:
Transform raw data from the repository into UI-ready state.
Maintain flags (loading, error, visibility, etc.).
Expose callback functions (commands) to the View for interactions.
Relationship: Views and ViewModels work in 1:1 pairs per feature. Example: LoginView ↔ LoginViewModel.
ViewModels
ViewModels
ViewModels
ViewModels
ViewModels are the heart of the UI layer. Their responsibilities include:
Fetching data from repositories
Filtering, sorting, and preparing data for display
Managing UI-specific states like toggles or scroll position
Exposing callback functions (commands) triggered by the view
💡 Every feature in your app should ideally have one View and one ViewModel.
Example:
LoginView+LoginViewModelLogoutView+LogoutViewModel(which can even be a button embedded into multiple widgets)
A view is not a widget—it can be a combination of widgets that represent a feature.
ViewModels are the heart of the UI layer. Their responsibilities include:
Fetching data from repositories
Filtering, sorting, and preparing data for display
Managing UI-specific states like toggles or scroll position
Exposing callback functions (commands) triggered by the view
💡 Every feature in your app should ideally have one View and one ViewModel.
Example:
LoginView+LoginViewModelLogoutView+LogoutViewModel(which can even be a button embedded into multiple widgets)
A view is not a widget—it can be a combination of widgets that represent a feature.
ViewModels are the heart of the UI layer. Their responsibilities include:
Fetching data from repositories
Filtering, sorting, and preparing data for display
Managing UI-specific states like toggles or scroll position
Exposing callback functions (commands) triggered by the view
💡 Every feature in your app should ideally have one View and one ViewModel.
Example:
LoginView+LoginViewModelLogoutView+LogoutViewModel(which can even be a button embedded into multiple widgets)
A view is not a widget—it can be a combination of widgets that represent a feature.
ViewModels are the heart of the UI layer. Their responsibilities include:
Fetching data from repositories
Filtering, sorting, and preparing data for display
Managing UI-specific states like toggles or scroll position
Exposing callback functions (commands) triggered by the view
💡 Every feature in your app should ideally have one View and one ViewModel.
Example:
LoginView+LoginViewModelLogoutView+LogoutViewModel(which can even be a button embedded into multiple widgets)
A view is not a widget—it can be a combination of widgets that represent a feature.
Data Layer: Repositories & Services
Data Layer: Repositories & Services
Data Layer: Repositories & Services
Data Layer: Repositories & Services
Repositories
Repositories are the single source of truth for app data. They:
Call services to fetch raw data
Convert raw responses into domain models
Handle caching, error handling, retries, and refreshes
Repositories connect directly with ViewModels, and multiple ViewModels can share one repository. They should never depend on each other, keeping your data flow unidirectional and easy to debug.
Services
Services live at the bottom of your app’s architecture. They:
Wrap APIs (REST, Firebase, GraphQL, etc.)
Talk to device features (like camera or GPS)
Read/write local files or preferences
Services return Future or Stream objects, and they contain no app logic.
💡 One service class per data source is a good rule of thumb.
Repositories
Repositories are the single source of truth for app data. They:
Call services to fetch raw data
Convert raw responses into domain models
Handle caching, error handling, retries, and refreshes
Repositories connect directly with ViewModels, and multiple ViewModels can share one repository. They should never depend on each other, keeping your data flow unidirectional and easy to debug.
Services
Services live at the bottom of your app’s architecture. They:
Wrap APIs (REST, Firebase, GraphQL, etc.)
Talk to device features (like camera or GPS)
Read/write local files or preferences
Services return Future or Stream objects, and they contain no app logic.
💡 One service class per data source is a good rule of thumb.
Repositories
Repositories are the single source of truth for app data. They:
Call services to fetch raw data
Convert raw responses into domain models
Handle caching, error handling, retries, and refreshes
Repositories connect directly with ViewModels, and multiple ViewModels can share one repository. They should never depend on each other, keeping your data flow unidirectional and easy to debug.
Services
Services live at the bottom of your app’s architecture. They:
Wrap APIs (REST, Firebase, GraphQL, etc.)
Talk to device features (like camera or GPS)
Read/write local files or preferences
Services return Future or Stream objects, and they contain no app logic.
💡 One service class per data source is a good rule of thumb.
Repositories
Repositories are the single source of truth for app data. They:
Call services to fetch raw data
Convert raw responses into domain models
Handle caching, error handling, retries, and refreshes
Repositories connect directly with ViewModels, and multiple ViewModels can share one repository. They should never depend on each other, keeping your data flow unidirectional and easy to debug.
Services
Services live at the bottom of your app’s architecture. They:
Wrap APIs (REST, Firebase, GraphQL, etc.)
Talk to device features (like camera or GPS)
Read/write local files or preferences
Services return Future or Stream objects, and they contain no app logic.
💡 One service class per data source is a good rule of thumb.
Optional: Domain Layer with Use-Cases
Optional: Domain Layer with Use-Cases
Optional: Domain Layer with Use-Cases
Optional: Domain Layer with Use-Cases
Why a Domain Layer?
In large apps, ViewModels can become bloated with logic. The Domain Layer helps by moving this logic into Use-Cases, also called Interactors.
Responsibilities of Use-Cases:
Combine data from multiple repositories
Contain complex business logic
Provide reusable logic to different ViewModels
Use-Cases:
Have well-defined inputs and outputs
Are easy to test in isolation
Improve code reusability across features
Use-Cases depend on Repositories. ViewModels depend on Use-Cases.
Use this layer only when needed. Don’t add use-cases for simple tasks unless they’re reused often.
Folder Structure Example
Pros & Cons of Adding a Domain Layer
Why a Domain Layer?
In large apps, ViewModels can become bloated with logic. The Domain Layer helps by moving this logic into Use-Cases, also called Interactors.
Responsibilities of Use-Cases:
Combine data from multiple repositories
Contain complex business logic
Provide reusable logic to different ViewModels
Use-Cases:
Have well-defined inputs and outputs
Are easy to test in isolation
Improve code reusability across features
Use-Cases depend on Repositories. ViewModels depend on Use-Cases.
Use this layer only when needed. Don’t add use-cases for simple tasks unless they’re reused often.
Folder Structure Example
Pros & Cons of Adding a Domain Layer
Why a Domain Layer?
In large apps, ViewModels can become bloated with logic. The Domain Layer helps by moving this logic into Use-Cases, also called Interactors.
Responsibilities of Use-Cases:
Combine data from multiple repositories
Contain complex business logic
Provide reusable logic to different ViewModels
Use-Cases:
Have well-defined inputs and outputs
Are easy to test in isolation
Improve code reusability across features
Use-Cases depend on Repositories. ViewModels depend on Use-Cases.
Use this layer only when needed. Don’t add use-cases for simple tasks unless they’re reused often.
Folder Structure Example
Pros & Cons of Adding a Domain Layer
Why a Domain Layer?
In large apps, ViewModels can become bloated with logic. The Domain Layer helps by moving this logic into Use-Cases, also called Interactors.
Responsibilities of Use-Cases:
Combine data from multiple repositories
Contain complex business logic
Provide reusable logic to different ViewModels
Use-Cases:
Have well-defined inputs and outputs
Are easy to test in isolation
Improve code reusability across features
Use-Cases depend on Repositories. ViewModels depend on Use-Cases.
Use this layer only when needed. Don’t add use-cases for simple tasks unless they’re reused often.
Folder Structure Example
Pros & Cons of Adding a Domain Layer
Top Questions Answered
Top Questions Answered
Top Questions Answered
Top Questions Answered
1. Is this architecture required?
No, but it’s highly recommended for apps beyond simple prototypes.
2. Can views have logic?
Only minimal UI logic. Business logic should go in ViewModels.
3. What’s the difference between a ViewModel and Use-Case?
ViewModels handle UI logic; Use-Cases handle reusable business logic.
4. Can one ViewModel use multiple repositories?
Yes! That’s often the case.
5. What if two features share logic?
Use a Use-Case so the logic can be reused.
6. Should services know about business logic?
No. They should only fetch data.
7. What is the benefit of a 1:1 View-ViewModel relationship?
It makes testing and maintenance simpler.
8. How should I test my ViewModel?
Mock the repository, then test the ViewModel’s state and outputs.
9. Can I skip the Domain layer?
Yes—unless complexity makes logic reuse or testing difficult.
10. Should repositories call each other?
No. Always combine data higher up (in the ViewModel or Domain).
1. Is this architecture required?
No, but it’s highly recommended for apps beyond simple prototypes.
2. Can views have logic?
Only minimal UI logic. Business logic should go in ViewModels.
3. What’s the difference between a ViewModel and Use-Case?
ViewModels handle UI logic; Use-Cases handle reusable business logic.
4. Can one ViewModel use multiple repositories?
Yes! That’s often the case.
5. What if two features share logic?
Use a Use-Case so the logic can be reused.
6. Should services know about business logic?
No. They should only fetch data.
7. What is the benefit of a 1:1 View-ViewModel relationship?
It makes testing and maintenance simpler.
8. How should I test my ViewModel?
Mock the repository, then test the ViewModel’s state and outputs.
9. Can I skip the Domain layer?
Yes—unless complexity makes logic reuse or testing difficult.
10. Should repositories call each other?
No. Always combine data higher up (in the ViewModel or Domain).
1. Is this architecture required?
No, but it’s highly recommended for apps beyond simple prototypes.
2. Can views have logic?
Only minimal UI logic. Business logic should go in ViewModels.
3. What’s the difference between a ViewModel and Use-Case?
ViewModels handle UI logic; Use-Cases handle reusable business logic.
4. Can one ViewModel use multiple repositories?
Yes! That’s often the case.
5. What if two features share logic?
Use a Use-Case so the logic can be reused.
6. Should services know about business logic?
No. They should only fetch data.
7. What is the benefit of a 1:1 View-ViewModel relationship?
It makes testing and maintenance simpler.
8. How should I test my ViewModel?
Mock the repository, then test the ViewModel’s state and outputs.
9. Can I skip the Domain layer?
Yes—unless complexity makes logic reuse or testing difficult.
10. Should repositories call each other?
No. Always combine data higher up (in the ViewModel or Domain).
1. Is this architecture required?
No, but it’s highly recommended for apps beyond simple prototypes.
2. Can views have logic?
Only minimal UI logic. Business logic should go in ViewModels.
3. What’s the difference between a ViewModel and Use-Case?
ViewModels handle UI logic; Use-Cases handle reusable business logic.
4. Can one ViewModel use multiple repositories?
Yes! That’s often the case.
5. What if two features share logic?
Use a Use-Case so the logic can be reused.
6. Should services know about business logic?
No. They should only fetch data.
7. What is the benefit of a 1:1 View-ViewModel relationship?
It makes testing and maintenance simpler.
8. How should I test my ViewModel?
Mock the repository, then test the ViewModel’s state and outputs.
9. Can I skip the Domain layer?
Yes—unless complexity makes logic reuse or testing difficult.
10. Should repositories call each other?
No. Always combine data higher up (in the ViewModel or Domain).
Final Thoughts
Final Thoughts
Final Thoughts
Final Thoughts
Flutter’s recommended architecture strikes a beautiful balance between structure and flexibility. By cleanly separating UI, business logic, and data access, you make your app more modular, more testable, and easier to evolve.
Start with UI and Data layers using the MVVM pattern. Add a Domain Layer only when it solves a specific problem. Use architecture as a tool—not a cage—and adapt it as your app grows.
Flutter’s recommended architecture strikes a beautiful balance between structure and flexibility. By cleanly separating UI, business logic, and data access, you make your app more modular, more testable, and easier to evolve.
Start with UI and Data layers using the MVVM pattern. Add a Domain Layer only when it solves a specific problem. Use architecture as a tool—not a cage—and adapt it as your app grows.
Flutter’s recommended architecture strikes a beautiful balance between structure and flexibility. By cleanly separating UI, business logic, and data access, you make your app more modular, more testable, and easier to evolve.
Start with UI and Data layers using the MVVM pattern. Add a Domain Layer only when it solves a specific problem. Use architecture as a tool—not a cage—and adapt it as your app grows.
Flutter’s recommended architecture strikes a beautiful balance between structure and flexibility. By cleanly separating UI, business logic, and data access, you make your app more modular, more testable, and easier to evolve.
Start with UI and Data layers using the MVVM pattern. Add a Domain Layer only when it solves a specific problem. Use architecture as a tool—not a cage—and adapt it as your app grows.
Table of content
© 2021-25 Blupx Private Limited.
All rights reserved.
© 2021-25 Blupx Private Limited.
All rights reserved.
© 2021-25 Blupx Private Limited.
All rights reserved.
