All 7 Flutter Architecture Patterns (MVVM & Clean Architecture) questions
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What is Clean Architecture, and what are its three commonly referenced core layers, presentation, domain, and data? How do use cases, sometimes also called interactors, in Clean Architecture help encapsulate one single specific piece of application business logic, keeping it fully independent of any specific user interface or specific data source implementation? How does the repository pattern abstract away the specific technical details of exactly where data actually comes from, such as a remote API versus a local cache, from the rest of an app's business logic? How does properly separating business logic from a specific state management library, such as Provider or BLoC, help make that business logic genuinely reusable and considerably easier to test, regardless of which particular library you might actually choose to use? What are the practical tradeoffs of adopting a genuinely full, strict Clean Architecture approach for a Flutter app, in terms of both the additional required boilerplate code and the genuine long term maintainability benefits it actually provides? How do you properly test each individual distinct layer of a Clean Architecture based Flutter app, including the domain, data, and presentation layers, using genuinely appropriate distinct testing strategies for each one?
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What is the MVVM, or Model View ViewModel, architectural pattern, and how does it help clearly separate a Flutter app's user interface code from its underlying business logic?

Beginner

Answer

MVVM separates an application into three distinct, clearly defined parts, the Model representing the actual underlying data and core business rules, the View representing the visual widgets actually responsible for displaying that data to the user, and the ViewModel acting as an intermediary that prepares and exposes data specifically formatted for the View while also handling any user interactions, and this clean separation means the View itself can generally remain fairly simple and focused purely on layout and presentation, while the ViewModel handles the more meaningfully complex actual business logic, making both considerably easier to test and maintain fully independently of each other.
class ProductViewModel extends ChangeNotifier {
  List<Product> products = [];

  Future<void> loadProducts() async {
    products = await repository.fetchProducts();
    notifyListeners();
  }
}
Real-world example A product listing screen keeps its actual widget code focused purely on layout and displaying data, while a separate ProductViewModel handles fetching, sorting, and properly filtering the underlying product data, making the actual business logic considerably easier to test entirely independently of the user interface itself.

Common follow-ups: How does the ViewModel actually communicate a state change back to the View that needs to rebuild?;What is the difference between MVVM and the closely related MVC pattern?

State Management with Provider;Unit Testing in Flutter
All 7 Flutter Architecture Patterns (MVVM & Clean Architecture) questions