Application Architecture - Common Mistakes Fundamentals

An application can be beautiful on the outside, but if the internal architecture is bad, it will be slow, difficult to maintain, and full of bugs. Software Architecture defines how parts of the code are organized and talk to each other. It is the foundation of the building.

If you're starting or have inherited a legacy project, understand the fundamentals so you don't build a house of cards.

What is Good Architecture?

A good architecture should be:

Scalable: Easy to add new features without breaking old ones.
Testable: Easy to write automated tests.
Maintainable: Any new developer should understand the code quickly.

Common Standards (Alphabet Soup)

MVC (Model-View-Controller)

The classic.

Model: Data.
View: Screen.
Controller: Logic that connects the two.
Problem: In mobile apps, the Controller tends to become gigantic (Massive View Controller), concentrating too much responsibility.

MVVM (Model-View-ViewModel)

The modern industry standard (Android Jetpack, iOS Swift UI).

ViewModel: Prepares data specifically for the View to display. The View "observes" the ViewModel. If the data changes, the screen updates itself (Reactivity).
Advantage: It separates the logic from the interface very well.

Clean Architecture

Proposed by Robert C. Martin (Uncle Bob). Divides the app into layers (onion).

Core (Domain): Pure business rules (they don't know it's an app).
Data: Repositories, APIs, Database.
Presentation: UI, ViewModels. The rule is: The layers on the outside know the layers on the inside, but the layers on the inside DO NOT know the layers on the outside. The Core doesn't know if it's running on an iPhone or a microwave.

Fundamental Errors

Logic in the UI: Place business rules ("if balance < 0, color it red") directly in the screen file. This makes it impossible to test without running the emulator.
Strong Coupling: If you change the API library (Retrofit) and have to rewrite screens, your coupling is wrong. Use Dependency Injection.
God Objects: Classes that do everything (call API, save in the database, format data). Break into small classes with single responsibility (SOLID).

Conclusion

There is no "perfect architecture", there is the appropriate architecture for the size of the project. For an MVP, simple MVC will do. For a Super App, Clean Architecture is mandatory. The important thing is to choose a standard and follow it consistently.