MVVM vs. MVI: Choosing an App Architecture

Choosing the right architecture is one of the most critical decisions you'll make for your Android project. It dictates how your app handles data, manages state, and scales over time. For years, Google has recommended MVVM (Model-View-ViewModel) as the standard, but a powerful alternative, MVI (Model-View-Intent), has gained significant traction, especially in the world of Jetpack Compose.

This isn't a battle of which is "better." It's about understanding the philosophies behind each and choosing the right tool for the job. Let's break them down.

The Veteran: MVVM (Model-View-ViewModel)

MVVM is the architecture most Android developers are familiar with. It's battle-tested, well-documented, and fully supported by Android Jetpack components.

The Flow:

• View (Activity/Fragment/Composable): Observes data from the ViewModel (usually via LiveData or StateFlow) and sends user events (like button clicks) to it.
• ViewModel: Holds and exposes UI-related data. It receives events from the View, processes them (often by calling a Repository), and updates its data streams. The View automatically reacts to these updates.
• Model: The data layer (Repository, data sources, etc.) that the ViewModel uses to get and save data.

// ViewModel
class ProfileViewModel(private val repo: UserRepository) : ViewModel() {
    private val _user = MutableStateFlow<User?>(null)
    val user: StateFlow<User?> = _user

    private val _isLoading = MutableStateFlow(false)
    val isLoading: StateFlow<Boolean> = _isLoading

    // Event handler
    fun onButtonClicked(userId: String) {
        viewModelScope.launch {
            _isLoading.value = true
            _user.value = repo.getUser(userId)
            _isLoading.value = false
        }
    }
}

// View (Composable)
@Composable
fun ProfileScreen(viewModel: ProfileViewModel) {
    val user by viewModel.user.collectAsState()
    val isLoading by viewModel.isLoading.collectAsState()

    // ... display user and loading state
    Button(onClick = { viewModel.onButtonClicked("123") }) { /* ... */ }
}

Strengths of MVVM:

• Mature and Familiar: It's the industry standard with vast amounts of documentation and examples.
• Simple for Simple Screens: For screens with few states and events, it's very straightforward to implement.
• Excellent Jetpack Integration: Works seamlessly with ViewModel, LiveData, and StateFlow.

The Challenger: MVI (Model-View-Intent)

MVI introduces a more structured and predictable approach based on a core principle: unidirectional data flow. This means data flows in a single, cyclical loop, making state changes easier to reason about and debug.

The Flow:

• View: Renders a State object and emits Intents (not Android `Intent`s, but user actions like "LoadDataIntent" or "RefreshIntent"). The View is completely passive.
• ViewModel/Processor: Receives Intents, processes them, and creates a new State object.
• State: A single, immutable data class that represents the entire state of the screen at any given moment (e.g., `data`, `isLoading`, `error`). The View subscribes to this single stream of State objects.

// 1. Define State and Intent
data class ProfileState(
    val user: User? = null,
    val isLoading: Boolean = false
)
sealed class ProfileIntent {
    data class LoadUser(val userId: String) : ProfileIntent()
}

// 2. ViewModel
class ProfileViewModel(private val repo: UserRepository) : ViewModel() {
    private val _state = MutableStateFlow(ProfileState())
    val state: StateFlow<ProfileState> = _state

    fun processIntent(intent: ProfileIntent) {
        when (intent) {
            is ProfileIntent.LoadUser -> {
                viewModelScope.launch {
                    // Create a new state for loading
                    _state.value = _state.value.copy(isLoading = true)
                    val user = repo.getUser(intent.userId)
                    // Create a new state with the result
                    _state.value = _state.value.copy(user = user, isLoading = false)
                }
            }
        }
    }
}

// 3. View (Composable)
@Composable
fun ProfileScreen(viewModel: ProfileViewModel) {
    val state by viewModel.state.collectAsState()
    // ... display UI based on the single 'state' object
    Button(onClick = { viewModel.processIntent(ProfileIntent.LoadUser("123")) }) { /* ... */ }
}

Strengths of MVI:

• Predictable State: With a single state object, you always know exactly what the UI should be showing. This eliminates entire classes of bugs where different state streams (like in MVVM) could get out of sync.
• Easier Debugging: You can log every Intent and every resulting State change, giving you a perfect, reproducible timeline of what happened in your app.
• Great for Complex Screens: When you have many possible states and user interactions, MVI's structured approach prevents the ViewModel from becoming a mess of multiple `StateFlow`s and event handlers.

The Verdict: Which Should You Choose?

Choose MVVM if:

• Your team is already comfortable with it.
• Your screens are relatively simple.
• You want to stick closely to the standard Android Jetpack examples.

Choose MVI if:

• You are building screens with very complex state.
• You value state predictability and easy debugging above all else.
• Your team is open to learning a more structured, "reactive" way of thinking.
• You are working heavily with Jetpack Compose, as its philosophy aligns perfectly with MVI's single state object.

Many teams even use a hybrid approach, using MVVM for simple screens and MVI for more complex ones. The key is to understand the trade-offs and make a conscious decision that sets your project up for success.