How do you choose an architecture for a project?

When choosing an architecture, I consider the following factors:

• Size and complexity of the project: Simple applications may suffice with a simpler architecture (e.g., MVP), while larger and more complex projects are better suited for a multi-layered architecture (e.g., MVVM with Clean Architecture).
• Team and its experience: The level of the team's familiarity with various architectural patterns influences the choice. It's better to choose an architecture that most team members understand.
• Time and budget: Complex architectures require more time to implement but can reduce support costs in the future.
• Testability and maintainability requirements: The architecture should facilitate writing unit and integration tests, as well as simplify making changes to the code.
• Scalability: If the application is expected to actively develop, the architecture should allow easy addition of new features.

Common architectural patterns in Android:

• MVC (Model-View-Controller): Simple but has issues with testability of the Controller and tight coupling between View and Model.
• MVP (Model-View-Presenter): An improved version of MVC, where the Presenter acts as an intermediary between View and Model, increasing testability.
• MVVM (Model-View-ViewModel): A popular pattern that uses data binding to connect View and ViewModel, reducing boilerplate code.
• MVI (Model-View-Intent): A pattern based on a unidirectional data flow and immutable states, which simplifies debugging.

For small projects, MVVM can be used. For large and long-term projects, a combination of MVVM with Clean Architecture is preferable.

// Example of Clean Architecture structure with MVVM
// app/build.gradle
// ... dependencies for LiveData, ViewModel, Room, Retrofit, etc.

// domain layer (pure business logic)
// domain/usecase/GetUserDataUseCase.kt
interface GetUserDataUseCase {
    suspend fun execute(): UserData
}

// data layer (data sources: API, DB)
// data/repository/UserRepositoryImpl.kt
class UserRepositoryImpl(
    private val apiService: ApiService,
    private val userDao: UserDao
) : UserRepository {
    override suspend fun getUserData(): UserData {
        // logic to fetch data from API or DB
    }
}

// presentation layer (UI)
// presentation/ui/screens/user/UserViewModel.kt
class UserViewModel(
    private val getUserDataUseCase: GetUserDataUseCase
) : ViewModel() {
    private val _userData = MutableLiveData<UserData>()
    val userData: LiveData<UserData> = _userData

    fun loadUserData() {
        viewModelScope.launch {
            _userData.value = getUserDataUseCase.execute()
        }
    }
}