MVVM Architecture in Jetpack Compose

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MVVM Architecture in Jetpack Compose: A Complete Guide

Jetpack Compose is Android’s modern UI toolkit, which allows developers to build UIs in a declarative way. As apps grow in complexity, managing UI state and business logic efficiently becomes critical for maintaining scalable and maintainable code. One of the most widely used architecture patterns for achieving this separation of concerns is the MVVM (Model-View-ViewModel) pattern.

MVVM helps organize code by separating the UI (View), business logic (ViewModel), and data (Model). In Jetpack Compose, this architecture fits perfectly as the UI components are highly composable and work seamlessly with Jetpack libraries such as LiveData, StateFlow, and ViewModel.

In this article, we’ll discuss how to implement the MVVM pattern in Jetpack Compose and break down the roles of each component, followed by a step-by-step guide on building a simple app with MVVM architecture in Jetpack Compose.

What is MVVM Architecture?

MVVM is an architecture pattern designed to separate concerns into three components:

  1. Model: Represents the data and business logic. It includes repositories, network data sources, and local databases.
  2. View: Represents the UI layer. It displays data and listens for user interactions (e.g., clicks, text input). In Jetpack Compose, the @Composable functions serve as the View.
  3. ViewModel: Holds the logic for updating the View. It interacts with the Model to retrieve or update data and exposes that data to the View in a way that’s easy to observe. It also manages the lifecycle of the UI-related data.

The MVVM architecture ensures that the View doesn’t contain logic, only the responsibility of displaying the data provided by the ViewModel. The ViewModel doesn’t directly manipulate the UI but exposes data in a way the View can observe and react to.

Benefits of Using MVVM in Jetpack Compose

  1. Separation of Concerns: It decouples UI from business logic, making the code more modular and easier to test.
  2. Testability: The ViewModel can be tested without the UI, which makes it easier to write unit tests.
  3. Reactivity: Jetpack Compose is reactive in nature. The ViewModel exposes data as state, which the UI automatically reacts to when it changes.
  4. Lifecycle-Aware: The ViewModel is lifecycle-aware, meaning it persists across configuration changes (like screen rotations) without the need for manual handling of state.
  5. Cleaner Code: The structure of MVVM promotes cleaner, more maintainable code.

Key Components of MVVM Architecture in Jetpack Compose

1. Model

The Model is responsible for the data and business logic of the app. It can include:

  • Network APIs (e.g., Retrofit)
  • Local databases (e.g., Room)
  • Repositories that handle data retrieval and manipulation.

2. View

The View in Jetpack Compose is made up of @Composable functions, which are responsible for:

  • Displaying UI elements
  • Observing changes in the ViewModel
  • Handling user input and triggering events in the ViewModel

3. ViewModel

The ViewModel serves as the middleman between the View and the Model. It:

  • Fetches data from the Model (usually via repositories or other sources)
  • Exposes the data to the View via State or LiveData
  • Manages UI-related state

Step-by-Step Guide to Implementing MVVM in Jetpack Compose

Let’s walk through an example where we build a simple app that displays a list of users from a remote API. This example will use ViewModel, StateFlow, and Composable functions to implement the MVVM pattern.

1. Define the Model

First, let’s define a simple data model, User, which represents the user data.

data class User(
    val id: Int,
    val name: String,
    val email: String
)

Next, we’ll create a repository to handle data fetching. This repository will interact with a remote API to fetch the list of users.

class UserRepository {
    suspend fun getUsers(): List<User> {
        // Mocked data fetching (e.g., from a network or local database)
        return listOf(
            User(1, "John Doe", "john.doe@example.com"),
            User(2, "Jane Doe", "jane.doe@example.com")
        )
    }
}

2. Create the ViewModel

Now, let’s create the ViewModel. The ViewModel will be responsible for calling the UserRepository to fetch the user data and expose it to the View.

import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.launch

class UserViewModel(private val userRepository: UserRepository) : ViewModel() {

    // Exposing the state of the users as a StateFlow
    private val _users = MutableStateFlow<List<User>>(emptyList())
    val users: StateFlow<List<User>> = _users

    init {
        fetchUsers()
    }

    // Fetch users from the repository
    private fun fetchUsers() {
        viewModelScope.launch {
            val fetchedUsers = userRepository.getUsers()
            _users.value = fetchedUsers
        }
    }
}
  • StateFlow: This is used to hold and expose UI state in a lifecycle-aware manner.
  • viewModelScope.launch: This coroutine scope ensures that the data-fetching operation respects the lifecycle of the ViewModel.

3. Create the View (Composable)

The View in Jetpack Compose will consist of a @Composable function that observes the StateFlow from the ViewModel and displays the UI accordingly.

import androidx.compose.foundation.layout.*
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.material3.*
import androidx.compose.runtime.*
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp

@Composable
fun UserListScreen(viewModel: UserViewModel) {
    val users by viewModel.users.collectAsState()

    Scaffold(
        topBar = {
            TopAppBar(title = { Text("Users List") })
        },
        content = { paddingValues ->
            LazyColumn(modifier = Modifier.padding(paddingValues)) {
                items(users) { user ->
                    UserItem(user = user)
                }
            }
        }
    )
}

@Composable
fun UserItem(user: User) {
    Card(
        modifier = Modifier
            .fillMaxWidth()
            .padding(8.dp)
    ) {
        Column(
            modifier = Modifier.padding(16.dp)
        ) {
            Text("ID: ${user.id}")
            Text("Name: ${user.name}")
            Text("Email: ${user.email}")
        }
    }
}

@Preview(showBackground = true)
@Composable
fun PreviewUserListScreen() {
    val viewModel = UserViewModel(UserRepository())
    UserListScreen(viewModel = viewModel)
}
  • collectAsState(): This is a Jetpack Compose function that collects values from a StateFlow and triggers recomposition whenever the value changes.
  • Scaffold: The top-level structure of the screen, providing space for the app’s top bar, content, and other UI elements.

4. Set Up Dependency Injection (Optional)

For production apps, you might want to use a Dependency Injection (DI) framework like Hilt to inject the UserRepository and UserViewModel into the Composables.

@HiltViewModel
class UserViewModel @Inject constructor(private val userRepository: UserRepository) : ViewModel() {
    // Same implementation as before
}

Then, in your MainActivity:

@AndroidEntryPoint
class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            val viewModel: UserViewModel = hiltViewModel()
            UserListScreen(viewModel = viewModel)
        }
    }
}

Conclusion

The MVVM architecture in Jetpack Compose allows developers to create maintainable, scalable, and testable applications. By separating the UI (View), logic (ViewModel), and data (Model), MVVM ensures that each component has a clear responsibility.

Jetpack Compose’s declarative nature, combined with StateFlow and ViewModel, makes it incredibly easy to implement this architecture. You can efficiently manage state, handle UI updates, and keep the logic separate from the UI code, all while enjoying the simplicity and flexibility Jetpack Compose provides.

In this article, we covered:

  • The components of MVVM: Model, View, and ViewModel
  • How to implement MVVM in Jetpack Compose
  • Benefits of using MVVM in Compose apps

By following these principles, you can create apps that are easier to test, maintain, and scale.

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