Understanding MVI Architecture in Android Jetpack Compose

If you’re building Android apps with Jetpack Compose, you might have heard about different ways to organize your code. One popular method is called Model-View-Intent (MVI). Let’s break down what MVI is and how it works with Jetpack Compose in easy-to-understand terms.

What is MVI?

MVI stands for Model-View-Intent. It’s a way to organize your app’s code so it’s easier to manage and understand. Here’s what each part does:

1. Model: This is where your app’s data and logic live. It keeps track of what’s happening in your app and makes decisions based on that.

2. View: This is what your users see. It shows the current state of your app and lets users interact with it.

3. Intent: These are the actions that users take, like pressing a button. Intents tell the app what the user wants to do.

The magic of MVI is in how it keeps everything flowing in one direction: user actions (Intents) update the data (Model), and then the View shows the updated data.

Using MVI with Jetpack Compose

Jetpack Compose is a new way to build UIs in Android. Instead of dealing with lots of XML files, you can write your UI code in Kotlin, which is simpler and more intuitive. Here’s how MVI fits into this:

1. Define Your Model

Start by creating a class that holds the data your app needs. For example, if you’re building a counter app, your Model might look like this:

data class CounterState(val count: Int = 0)

2. Create Intents

Next, define what actions users can take. For a counter app, you might have:

sealed class CounterIntent {
    object Increment : CounterIntent()

    object Decrement : CounterIntent()
}

3. Set Up the ViewModel

The ViewModel is the middleman between the View and the Model. It handles the Intents and updates the Model accordingly. Here’s a simple ViewModel for our counter:

class CounterViewModel : ViewModel() {

    private val _state = MutableStateFlow(CounterState())
    val state: StateFlow
        get() = _state

    fun handleIntent(intent: CounterIntent) {
        when (intent) {
            is CounterIntent.Increment -> updateState { copy(count = count + 1) }
            is CounterIntent.Decrement -> updateState { copy(count = count - 1) }
        }
    }

    private fun updateState(reduce: CounterState.() -> CounterState) {
        _state.value = _state.value.reduce()
    }
}

4. Build the View with Compose

Now, create your UI using Jetpack Compose. This is where you show the data and handle user interactions. For our counter app:

@Composable
fun CounterScreen(viewModel: CounterViewModel = viewModel()) {
    val state by viewModel.state.collectAsState()

    Column(
        modifier = Modifier.fillMaxSize(),
        horizontalAlignment = Alignment.CenterHorizontally,
        verticalArrangement = Arrangement.Center
    ) {
        Text(text = "Count: ${state.count}", fontSize = 24.sp)
        Row {
            Button(onClick = { viewModel.handleIntent(CounterIntent.Increment) }) {
                Text("Increment")
            }
            Spacer(modifier = Modifier.width(8.dp))
            Button(onClick = { viewModel.handleIntent(CounterIntent.Decrement) }) {
                Text("Decrement")
            }
        }
    }
}

Why Use MVI with Jetpack Compose?

1. Predictable: MVI makes it easy to understand how data changes because everything flows in one direction.

2. Organized: It keeps your code clean by separating what your app does (Model), what it shows (View), and what users do (Intent).

3. Scalable: As your app grows, MVI helps keep things manageable by enforcing a clear structure.

Conclusion

Using MVI with Jetpack Compose is a great way to build Android apps. MVI helps you manage state and actions in a clear and predictable way, while Jetpack Compose makes building UIs simpler and more intuitive. Together, they make developing Android apps more efficient and enjoyable.