Building a Multi-Platform Mobile App with Kotlin Multiplatform and Jetpack Compose

In today’s rapidly evolving tech landscape, developers face increasing pressure to create applications that work seamlessly across multiple platforms. Kotlin Multiplatform (KMP) paired with Jetpack Compose offers a powerful solution for building cross-platform mobile applications. This article will delve into the essentials of KMP and Jetpack Compose, providing you with actionable insights, coding examples, and step-by-step instructions to help you create your multi-platform mobile app.

What is Kotlin Multiplatform?

Kotlin Multiplatform is an innovative feature of the Kotlin programming language that allows developers to write shared code that runs on multiple platforms, including Android, iOS, web, and desktop. By enabling code sharing, KMP reduces development time and improves maintainability, as you can implement business logic once and reuse it across different platforms.

Key Benefits of Kotlin Multiplatform

• Code Reusability: Write business logic once and share it across platforms.
• Faster Development: Reduce duplication of effort, leading to quicker time-to-market.
• Flexibility: Use platform-specific APIs when needed while maintaining shared code.

What is Jetpack Compose?

Jetpack Compose is Android’s modern toolkit for building native user interfaces. It simplifies UI development by enabling developers to work with a declarative programming model rather than the traditional imperative model. This means you can describe the UI in a more intuitive way, leveraging Kotlin's features to create responsive and interactive applications.

Why Use Jetpack Compose?

• Less Boilerplate: Write less code to achieve the same functionality.
• Real-Time UI Updates: Efficiently update the UI in response to state changes.
• Seamless Integration: Easily combine with existing Android apps and libraries.

Setting Up Your Development Environment

Before diving into coding, ensure you have the following tools installed:

1. Android Studio: The official IDE for Android development.
2. Kotlin Plugin: Typically included with Android Studio.
3. Kotlin Multiplatform Plugin: To enable KMP features.
4. Gradle: For managing dependencies.

Step 1: Create a New Project

1. Open Android Studio and select “New Project.”
2. Choose “Kotlin Multiplatform App” as your project type.
3. Configure your project settings, then click “Finish.”

Step 2: Configure the Gradle Files

In your build.gradle.kts file, set up the shared module:

kotlin {
    // Define targets
    ios() // iOS target
    android() // Android target

    sourceSets {
        val commonMain by getting {
            dependencies {
                implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.5.1")
            }
        }
        val androidMain by getting
        val iosMain by getting
    }
}

This configuration allows you to share code between Android and iOS by defining common and platform-specific source sets.

Building Shared Logic

Let’s create a simple shared business logic component. This will be a ViewModel that fetches data from a remote server.

Step 3: Create a Shared ViewModel

In the commonMain source set, create a new Kotlin file named SharedViewModel.kt:

import kotlinx.coroutines.GlobalScope
import kotlinx.coroutines.launch

class SharedViewModel {
    private val dataRepository = DataRepository()

    fun fetchData(onResult: (List<String>) -> Unit) {
        GlobalScope.launch {
            val data = dataRepository.getData() // Fetch data from repository
            onResult(data)
        }
    }
}

class DataRepository {
    suspend fun getData(): List<String> {
        // Simulate network call
        return listOf("Item 1", "Item 2", "Item 3")
    }
}

Step 4: Create the UI with Jetpack Compose

Now that we have the shared logic in place, let’s build the UI using Jetpack Compose. In your Android-specific source set, create a new file named MainActivity.kt:

import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.remember
import androidx.compose.ui.tooling.preview.Preview

class MainActivity : ComponentActivity() {
    private val viewModel = SharedViewModel()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            MyApp()
        }
    }

    @Composable
    fun MyApp() {
        val data = remember { mutableStateListOf<String>() }

        LaunchedEffect(Unit) {
            viewModel.fetchData {
                data.clear()
                data.addAll(it)
            }
        }

        // Display the data
        DisplayData(data)
    }

    @Composable
    fun DisplayData(items: List<String>) {
        items.forEach { item ->
            Text(text = item)
        }
    }

    @Preview
    @Composable
    fun PreviewMyApp() {
        MyApp()
    }
}

Step 5: Run Your Application

1. Select your Android device or emulator.
2. Click on the “Run” button in Android Studio to build and deploy your application.

Troubleshooting Common Issues

Issue: Dependencies Not Found

Ensure that your Gradle files are correctly configured and that you have synced your project. If a dependency fails to resolve, try invalidating caches and restarting Android Studio.

Issue: UI Not Updating

If the UI does not reflect changes after data fetching, ensure that you are using state management correctly with mutableStateListOf.

Conclusion

Building a multi-platform mobile app with Kotlin Multiplatform and Jetpack Compose empowers developers to create efficient, maintainable applications across Android and iOS. By leveraging shared code and a declarative UI, you can significantly streamline your development process.

With the foundational concepts and practical coding examples provided in this article, you’re now equipped to embark on your cross-platform app development journey. Embrace the power of Kotlin Multiplatform and Jetpack Compose, and watch your productivity soar!