Networking in Compose Multiplatform: A Comprehensive Guide

Building multiplatform applications with Jetpack Compose allows developers to target multiple platforms (Android, iOS, Desktop, Web) using a single codebase. When these applications need to communicate with external services, networking becomes a crucial aspect. This blog post explores how to handle networking in a Compose Multiplatform app using Kotlin Multiplatform libraries and Jetpack Compose.

Understanding Networking in Compose Multiplatform

Networking in a Compose Multiplatform app involves making HTTP requests, handling responses, and managing data serialization and deserialization. Due to the platform-specific nature of networking, Kotlin Multiplatform provides mechanisms to abstract these differences and offer a unified API.

Why Kotlin Multiplatform Networking?

• Code Reusability: Share networking logic across multiple platforms.
• Unified API: Use consistent APIs for making network requests, regardless of the platform.
• Platform-Specific Implementations: Leverage native networking capabilities for each platform when necessary.

Implementing Networking in a Compose Multiplatform App

To implement networking, we’ll use a combination of Kotlin Multiplatform libraries such as Ktor for making HTTP requests and kotlinx.serialization for handling data serialization and deserialization.

Step 1: Set Up Dependencies

In your build.gradle.kts file (or build.gradle), add the necessary dependencies. Here’s how to set up dependencies in the commonMain source set:

kotlin {
    sourceSets {
        val commonMain by getting {
            dependencies {
                implementation("io.ktor:ktor-client-core:2.3.2")
                implementation("io.ktor:ktor-client-serialization:2.3.2")
                implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.0")
            }
        }
        val androidMain by getting {
            dependencies {
                implementation("io.ktor:ktor-client-android:2.3.2")
            }
        }
        val iosMain by getting {
            dependencies {
                implementation("io.ktor:ktor-client-darwin:2.3.2")
            }
        }
    }
}

For native platforms (iOS and Android), include the respective platform-specific Ktor client engines (ktor-client-android for Android and ktor-client-darwin for iOS).

Step 2: Define Data Models

Define the data models using kotlinx.serialization. These models represent the data you will receive from the API.

import kotlinx.serialization.Serializable

@Serializable
data class Post(
    val userId: Int,
    val id: Int,
    val title: String,
    val body: String
)

Step 3: Create a Networking Client

Create a networking client using Ktor to make HTTP requests. Encapsulate the client within a class or object for reusability.

import io.ktor.client.*
import io.ktor.client.call.*
import io.ktor.client.plugins.contentnegotiation.*
import io.ktor.client.request.*
import io.ktor.serialization.kotlinx.json.*
import kotlinx.serialization.json.Json

object NetworkingClient {
    private val httpClient = HttpClient {
        install(ContentNegotiation) {
            json(Json {
                ignoreUnknownKeys = true
                isLenient = true
            })
        }
    }

    private const val BASE_URL = "https://jsonplaceholder.typicode.com"

    suspend fun getPosts(): List<Post> {
        return httpClient.get("$BASE_URL/posts").body()
    }
}

Key aspects of this networking client:

• Ktor HttpClient: The core client for making HTTP requests.
• Content Negotiation: Configured to handle JSON serialization using kotlinx.serialization.
• Base URL: A constant for the base URL of the API.
• getPosts Function: An example function to fetch a list of posts from a sample API.

Step 4: Implement Data Fetching in Compose UI

In your Compose UI, use the networking client to fetch data and display it.

import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.items
import androidx.compose.material.Text
import androidx.compose.runtime.*

@Composable
fun PostListScreen() {
    var posts by remember { mutableStateOf(emptyList<Post>()) }
    var errorMessage by remember { mutableStateOf<String?>(null) }

    LaunchedEffect(Unit) {
        try {
            posts = NetworkingClient.getPosts()
        } catch (e: Exception) {
            errorMessage = "Failed to fetch posts: ${e.message}"
        }
    }

    if (errorMessage != null) {
        Text("Error: ${errorMessage!!}")
    } else {
        LazyColumn {
            items(posts) { post ->
                Text("${post.title}")
            }
        }
    }
}

Here’s what this code does:

• State Management: Uses remember and mutableStateOf to store the list of posts and any error messages.
• LaunchedEffect: Launches a coroutine to fetch posts when the composable is first launched.
• Error Handling: Catches any exceptions that occur during the networking operation and displays an error message.
• UI Display: Uses LazyColumn to efficiently display the list of posts.

Step 5: Platform-Specific Considerations

Each platform may require specific configurations to handle networking properly.

Android

Ensure your Android app has the necessary permissions to access the internet. Add the INTERNET permission to your AndroidManifest.xml file.

<uses-permission android:name="android.permission.INTERNET&"/>

iOS

In iOS, you may need to configure the Info.plist file to allow arbitrary loads or specify the domains your app is allowed to communicate with. Add the following entry to your Info.plist.

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSAllowsArbitraryLoads</key>
    <true/>
</dict>

Handling Errors and Loading States

Proper error handling and loading state management are essential for providing a good user experience. Implement UI elements to indicate loading and display error messages when necessary.

import androidx.compose.material.CircularProgressIndicator
import androidx.compose.ui.Alignment
import androidx.compose.foundation.layout.*
import androidx.compose.ui.Modifier

@Composable
fun PostListScreen() {
    var posts by remember { mutableStateOf(emptyList<Post>()) }
    var errorMessage by remember { mutableStateOf<String?>(null) }
    var isLoading by remember { mutableStateOf(true) }

    LaunchedEffect(Unit) {
        isLoading = true
        try {
            posts = NetworkingClient.getPosts()
        } catch (e: Exception) {
            errorMessage = "Failed to fetch posts: ${e.message}"
        } finally {
            isLoading = false
        }
    }

    if (isLoading) {
        Box(modifier = Modifier.fillMaxSize(), contentAlignment = Alignment.Center) {
            CircularProgressIndicator()
        }
    } else if (errorMessage != null) {
        Text("Error: ${errorMessage!!}")
    } else {
        LazyColumn {
            items(posts) { post ->
                Text("${post.title}")
            }
        }
    }
}

Conclusion

Building networking capabilities in a Compose Multiplatform application requires leveraging Kotlin Multiplatform libraries such as Ktor and kotlinx.serialization. By abstracting platform-specific details, you can create reusable networking logic that works across multiple platforms. Properly handling errors and managing loading states are crucial for providing a seamless user experience. By following these steps, you can create robust and efficient networking layers in your Compose Multiplatform applications.