Architecture Patterns for Compose Multiplatform Apps with Jetpack Compose

With the advent of Compose Multiplatform, building applications that target multiple platforms with a shared codebase has become a reality. Leveraging effective architecture patterns is essential to maintaining scalability, testability, and maintainability in these multiplatform projects. This post delves into various architecture patterns suitable for Compose Multiplatform projects using Jetpack Compose.

What is Compose Multiplatform?

Compose Multiplatform, powered by Jetpack Compose, is a declarative UI framework that allows you to build applications that run on Android, iOS, desktop, and web platforms from a single codebase. This reduces development time and effort while maintaining platform-specific user experiences.

Why is Architecture Important in Compose Multiplatform?

• Code Sharing: Proper architecture maximizes code reuse across different platforms.
• Maintainability: Clear architecture enhances code maintainability and scalability.
• Testability: Well-defined layers enable easier testing of individual components.
• Platform Adaptability: Simplifies platform-specific customizations.

Common Architecture Patterns for Compose Multiplatform

Here are several architecture patterns that you can employ for building Compose Multiplatform applications:

1. Model-View-Intent (MVI)

MVI is a reactive architecture pattern that ensures a unidirectional data flow. It revolves around three core components:

• Model (State): Represents the state of the UI.
• View (Composable): Observes the state and renders the UI accordingly.
• Intent (Actions): User actions that trigger state changes.

In MVI, the View dispatches an Intent to the ViewModel (or Presenter). The ViewModel processes the Intent and updates the Model, which in turn updates the View. The unidirectional data flow simplifies state management and testing.

Implementation Example:

First, define the State, Intent, and ViewModel interfaces or classes.

// State
data class CounterState(val count: Int = 0)

// Intent
sealed class CounterIntent {
    object Increment : CounterIntent()
    object Decrement : CounterIntent()
}

// ViewModel (Using Kotlin's coroutines)
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.launch
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope

class CounterViewModel : ViewModel() {
    private val _state = MutableStateFlow(CounterState())
    val state: StateFlow = _state.asStateFlow()

    fun processIntent(intent: CounterIntent) {
        viewModelScope.launch {
            when (intent) {
                CounterIntent.Increment -> _state.value = _state.value.copy(count = _state.value.count + 1)
                CounterIntent.Decrement -> _state.value = _state.value.copy(count = _state.value.count - 1)
            }
        }
    }
}

Next, integrate these components within your Compose UI.

import androidx.compose.runtime.collectAsState
import androidx.compose.runtime.Composable
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.material3.Button
import androidx.compose.material3.Text
import androidx.compose.runtime.getValue

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

    Column {
        Text(text = "Count: ${state.count}")
        Row {
            Button(onClick = { viewModel.processIntent(CounterIntent.Increment) }) {
                Text("Increment")
            }
            Button(onClick = { viewModel.processIntent(CounterIntent.Decrement) }) {
                Text("Decrement")
            }
        }
    }
}

@Preview
@Composable
fun PreviewCounterView() {
    CounterView(viewModel = CounterViewModel())
}

2. Model-View-ViewModel (MVVM)

MVVM separates the UI from the business logic through the following components:

• Model: Represents the data and business logic.
• View: The UI that observes the ViewModel.
• ViewModel: Provides data to the View and handles user interactions.

MVVM is commonly used in Android development and is also suitable for Compose Multiplatform. The ViewModel exposes streams of data that the View observes. Actions from the View trigger functions in the ViewModel, which update the data.

Implementation Example:

Here is the ViewModel for a simple counter application.

import androidx.lifecycle.ViewModel
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.asStateFlow

class CounterViewModel : ViewModel() {
    private val _count = MutableStateFlow(0)
    val count: StateFlow = _count.asStateFlow()

    fun increment() {
        _count.value = _count.value + 1
    }

    fun decrement() {
        _count.value = _count.value - 1
    }
}

Here is the View.

import androidx.compose.runtime.collectAsState
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.material3.Button
import androidx.compose.material3.Text

@Composable
fun CounterView(viewModel: CounterViewModel) {
    val count by viewModel.count.collectAsState()

    Column {
        Text(text = "Count: $count")
        Row {
            Button(onClick = { viewModel.increment() }) {
                Text("Increment")
            }
            Button(onClick = { viewModel.decrement() }) {
                Text("Decrement")
            }
        }
    }
}

@Preview
@Composable
fun PreviewCounterView() {
    CounterView(viewModel = CounterViewModel())
}

3. Clean Architecture

Clean Architecture aims to create loosely coupled, independent modules, enhancing testability and maintainability. The core principle involves dividing the application into layers:

• Entities: Business objects of the application.
• Use Cases: Defines business rules.
• Interface Adapters: Converts data from use cases to a format suitable for UI.
• Frameworks and Drivers: External libraries, UI frameworks, and other infrastructure components.

In a Compose Multiplatform context, the UI layer (Composables) sits within the Frameworks and Drivers layer, interacting with the ViewModel in the Interface Adapters layer, which then invokes Use Cases and utilizes Entities.

Due to its complexity, implementing a complete Clean Architecture example here is not feasible. However, the essence is to decouple layers using interfaces and dependency injection. Each layer is testable in isolation, making the system more robust.

4. Feature-First Architecture

The Feature-First architecture organizes code by features, which can be advantageous in Compose Multiplatform because different platforms may need variations of specific features. This pattern focuses on creating self-contained modules that encapsulate all aspects of a single feature, from UI components to business logic.

Example:

Suppose you’re building a multiplatform application with an authentication feature. You might structure your project like this:

- src/
  - commonMain/
    - Authentication/
      - ui/
        - LoginScreen.kt
        - RegistrationScreen.kt
      - domain/
        - models/
          - User.kt
        - usecases/
          - LoginUseCase.kt
          - RegistrationUseCase.kt
      - data/
        - AuthRepository.kt

This isolates the authentication logic into its own module, making it easier to modify or extend without affecting other parts of the application. Each feature (module) contains all necessary UI components, business logic, and data access layers.

Choosing the Right Architecture

Selecting an architecture pattern depends on the complexity and scale of your project:

• MVI: Best for applications requiring strict unidirectional data flow and fine-grained control over state management.
• MVVM: A good balance between simplicity and testability, ideal for medium-sized projects.
• Clean Architecture: Suitable for large, complex applications that require high levels of testability and maintainability.
• Feature-First Architecture: Beneficial for modular projects where features may vary significantly across platforms.

Conclusion

Developing Compose Multiplatform applications demands careful consideration of architectural patterns. Whether you choose MVI, MVVM, Clean Architecture, or a Feature-First approach, the key is to establish clear separations of concerns and maintainability from the outset. Each pattern offers different advantages and tradeoffs, so align your architectural choices with your project’s specific needs and long-term goals. Properly implemented, these architecture patterns ensure scalability, maintainability, and a high degree of code reuse across multiple platforms.