Compose Multiplatform Architecture: Building Scalable Jetpack Compose Apps

Jetpack Compose has revolutionized Android UI development with its declarative approach, making UI creation more intuitive and efficient. Building upon this, Compose Multiplatform allows you to share your UI code across various platforms such as Android, iOS, Desktop (JVM), and Web. However, developing a multiplatform application demands a well-thought-out architecture to ensure code maintainability, testability, and scalability. This blog post explores robust architecture patterns tailored for Compose Multiplatform projects.

Why a Solid Architecture Matters for Compose Multiplatform

When creating multiplatform applications, architectural decisions significantly impact the project’s long-term success. A well-structured architecture can lead to:

• Code Reusability: Maximize code sharing across different platforms.
• Maintainability: Simplify updates and debugging across the project.
• Testability: Enable comprehensive testing of shared components.
• Scalability: Support future growth and additional features without overwhelming the codebase.

Core Architectural Principles

Before diving into specific architectural patterns, let’s establish some foundational principles:

1. Separation of Concerns (SoC): Divide the application into distinct sections, each handling a specific responsibility.
2. Single Responsibility Principle (SRP): Ensure that each class, function, or module has one specific job to do.
3. Dependency Inversion Principle (DIP): Depend upon abstractions rather than concretions to enable flexibility and testing.
4. Layered Architecture: Organize the codebase into distinct layers (e.g., UI, Business Logic, Data).

Proposed Architecture Layers for Compose Multiplatform

A suitable architecture for Compose Multiplatform can be divided into three primary layers:

1. Presentation Layer (UI):
   • Composables and related UI elements are placed here. This layer focuses on displaying data and handling user interactions.
   • Leverage Jetpack Compose for building UIs across multiple platforms.
2. Business Logic Layer (Domain):
   • Contains business rules, state management, and interaction logic.
   • Houses ViewModels, Use Cases/Interactors, and other components that coordinate data flow between UI and Data layers.
3. Data Layer:
   • Deals with data retrieval and persistence from various sources (e.g., APIs, databases, local storage).
   • Contains repositories, data sources, and model classes responsible for data operations.

Architectural Patterns for Compose Multiplatform

Here are the architectural patterns to consider for your Jetpack Compose Multiplatform Project.

1. Model-View-ViewModel (MVVM)

MVVM is a widely used pattern in modern Android development and can be effectively applied to Compose Multiplatform. MVVM enhances UI testability, maintainability, and separation of concerns.

Components of MVVM in Compose Multiplatform:

• Model:
  • Represents the data required to display or operate in the UI. These can be simple data classes.
• View:
  • The composable functions render UI components, observe state changes from ViewModel, and propagate user actions to ViewModel.
• ViewModel:
  • A class that holds and manages UI-related data in a lifecycle-conscious way.
  • It exposes data streams for the UI to observe and mediates between the View and the Model layers.

Implementation:

Consider a simple counter app. Here is the Kotlin Code.

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

// ViewModel (Shared Code)
import dev.icerock.moko.mvvm.viewmodel.ViewModel
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.launch

class CounterViewModel : ViewModel() {
    private val _state = MutableStateFlow(CounterState())
    val state: StateFlow<CounterState> = _state

    fun increment() {
        viewModelScope.launch {
            _state.value = _state.value.copy(count = _state.value.count + 1)
        }
    }
}

// View (Composable - Platform Specific)
import androidx.compose.foundation.layout.Column
import androidx.compose.material.Button
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.collectAsState
import androidx.compose.runtime.getValue

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

    Column {
        Text("Count: ${state.count}")
        Button(onClick = { viewModel.increment() }) {
            Text("Increment")
        }
    }
}

Benefits:

• Improved testability due to separated concerns.
• Clear separation between UI logic and business logic.
• Easy state management and UI updates with StateFlow.

2. Model-View-Intent (MVI)

MVI is a reactive architectural pattern that focuses on unidirectional data flow. It introduces the concept of “Intents,” representing the user’s intention to perform an action.

Components of MVI in Compose Multiplatform:

• Model (State):
  • Represents the immutable state of the UI.
• View:
  • Renders UI based on the current state and emits user Intents.
• Intent:
  • Represents a user action or intention to change the state.
• ViewModel (Reducer/Processor):
  • Processes Intents, updates the State, and notifies the View.

Implementation:

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

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

// ViewModel
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow

class CounterViewModel {
    private val _state = MutableStateFlow(CounterState())
    val state: StateFlow<CounterState> = _state

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

// View (Composable)
import androidx.compose.foundation.layout.Column
import androidx.compose.material.Button
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.collectAsState
import androidx.compose.runtime.getValue

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

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

Benefits:

• Enforces a clear unidirectional data flow.
• Simplified debugging due to immutable state.
• Supports advanced features like time-travel debugging and state restoration.

3. Clean Architecture

Clean Architecture is a comprehensive architectural pattern that aims to build highly maintainable, testable, and independent systems. It enforces clear boundaries between different application layers and isolates business logic from UI and external dependencies.

Key Components:

• Entities:
  • Represent the core business objects with application-independent logic.
• Use Cases:
  • Describe how entities are used in different operations of the application.
• Interface Adapters:
  • Convert data from formats convenient for Use Cases and Entities to formats convenient for external agencies like the Database or the Web.
• Frameworks and Drivers:
  • Composed of UI, tools, and external libraries/frameworks.

Benefits:

• High level of abstraction and separation of concerns.
• Enhanced testability as each layer can be tested independently.
• Better maintainability and adaptability to changes in external frameworks.

Common Components Across Patterns

Irrespective of the architecture chosen, some key components remain consistent across different patterns.

Repositories

Repositories mediate between data sources and the domain layer. They encapsulate data access logic, making it easier to switch between different data sources without affecting the rest of the application.

Use Cases/Interactors

Use Cases define specific interactions in the system. They orchestrate data flow using the repositories, enabling reusability of business logic across different UI components.

Dependency Injection (DI)

Dependency Injection helps manage dependencies within the application, facilitating loose coupling and improving testability. Common DI frameworks in Kotlin include Koin, Dagger/Hilt, and Kodein.

Key Multiplatform Libraries

Consider incorporating these libraries into your multiplatform project to boost efficiency and code reusability.

• Ktor: For building networking layers.
• SQLDelight: For database management across platforms.
• Kotlinx.serialization: For serializing data in JSON or other formats.
• moko-mvvm: For implementing MVVM pattern in Kotlin Multiplatform projects
• Decompose: A Kotlin Multiplatform library for implementing UI Navigation and lifecycle-aware components.

Example of Folder Structure

- shared
  - src
    - commonMain
      - kotlin
        - data
          - api
          - db
          - repository
        - domain
          - model
          - usecase
        - presentation
          - viewmodel
        - CommonConstants.kt
    - androidMain
    - iosMain

Conclusion

Crafting a solid architecture for your Compose Multiplatform project is crucial for ensuring code reusability, maintainability, and scalability. Whether you opt for MVVM, MVI, Clean Architecture, or a blend of these, understanding the underlying principles and utilizing appropriate libraries is key. Adopt these architectural patterns, use essential libraries, and organize the folder structure to achieve a flexible and robust multiplatform app. This will streamline development efforts and offer better testability for long-term success.