Jetpack Compose: Achieve Multiplatform Interoperability

Jetpack Compose has revolutionized Android UI development by offering a declarative and reactive approach. However, in many real-world scenarios, existing codebases might be written in traditional Android views, or even shared across different platforms with Kotlin Multiplatform. Compose multiplatform interoperability refers to the ability to seamlessly integrate Compose UI elements with existing Android View-based UIs and code shared via Kotlin Multiplatform.

Understanding Compose Multiplatform Interoperability

The ability to interoperate between Jetpack Compose and existing systems is crucial for the gradual adoption of Compose in large, established projects. Interoperability ensures that developers can migrate their UIs piece by piece, leveraging the benefits of Compose without rewriting entire applications from scratch. For Kotlin Multiplatform projects, this allows UI code to be shared across platforms while still integrating natively with platform-specific UI toolkits like Jetpack Compose on Android.

Why is Interoperability Important?

• Gradual Migration: Migrate existing Android View-based applications to Compose incrementally.
• Code Reusability: Reuse code written in traditional Android views or shared Kotlin Multiplatform modules.
• Flexibility: Choose the best UI framework for each specific component in your application.
• Reduced Risk: Minimize risk during migration by integrating Compose progressively.

Compose and Android Views Interoperability

1. Using ComposeView in an Android View

To embed Compose UI inside a traditional Android View, you can use ComposeView. This allows you to host Compose content within a standard Android layout.

Step 1: Add Dependencies

Make sure you have the necessary dependencies in your build.gradle file:

dependencies {
    implementation("androidx.compose.ui:ui:1.6.1")
    implementation("androidx.compose.ui:ui-tooling-preview:1.6.1")
    debugImplementation("androidx.compose.ui:ui-tooling:1.6.1")
    implementation("androidx.activity:activity-compose:1.9.0")
    implementation("androidx.appcompat:appcompat:1.7.0-alpha03")
}

Step 2: Integrate ComposeView in XML Layout

Add a ComposeView to your XML layout file:

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Traditional Android View" />

    <androidx.compose.ui.platform.ComposeView
        android:id="@+id/composeView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

Step 3: Set Content in Activity/Fragment

In your Activity or Fragment, find the ComposeView and set its content:

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.TextView
import androidx.compose.material.Text
import androidx.compose.ui.platform.ComposeView
import androidx.compose.ui.graphics.Color

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val textView: TextView = findViewById(R.id.textView)
        textView.text = "Hello from Android Views!"

        val composeView: ComposeView = findViewById(R.id.composeView)
        composeView.setContent {
            Text(text = "Hello from Jetpack Compose!", color = Color.Blue)
        }
    }
}

2. Using AndroidView in Compose

Conversely, to use an Android View inside Compose UI, you can use the AndroidView composable.

Step 1: Implement AndroidView

Embed an Android View in Compose:

import androidx.compose.runtime.Composable
import androidx.compose.ui.viewinterop.AndroidView
import android.widget.TextView
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.dp
import androidx.compose.foundation.layout.padding

@Composable
fun TextViewInCompose() {
    AndroidView(
        factory = { context ->
            TextView(context).apply {
                text = "Hello from Android View inside Compose!"
                textSize = 20f
            }
        },
        update = { textView ->
            // Update the view with new data or state changes
        },
        modifier = Modifier.padding(16.dp)
    )
}

Compose Multiplatform Interoperability

Sharing UI Components with Kotlin Multiplatform

Kotlin Multiplatform enables sharing business logic across different platforms. For UI, interoperability means sharing data and logic from the common module to platform-specific Compose UI.

Step 1: Set Up a Kotlin Multiplatform Project

Create a Kotlin Multiplatform project and define your UI-related data and logic in the common module.

Step 2: Define Common UI Data

In your common module (e.g., commonMain), define data classes and interfaces that describe the UI state:

package com.example.shared

data class UiState(val message: String)

interface UiController {
    fun updateMessage(newMessage: String)
}

Step 3: Implement UI Controller in Android

Implement the UiController in your Android Compose UI:

import androidx.compose.runtime.*
import com.example.shared.UiController
import com.example.shared.UiState
import androidx.compose.material.Text
import androidx.compose.ui.graphics.Color

class AndroidUiController : UiController {
    private val _uiState = mutableStateOf(UiState("Initial Message"))
    val uiState: State<UiState> = _uiState

    override fun updateMessage(newMessage: String) {
        _uiState.value = UiState(newMessage)
    }
}

@Composable
fun SharedTextComponent(uiController: AndroidUiController) {
    val state = uiController.uiState.value
    Text(text = state.message, color = Color.Green)
}

Step 4: Use Shared Components in Compose

In your Compose layout, use the shared UI component and the Android-specific controller:

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.compose.material.Button
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.ui.platform.ComposeView
import com.example.shared.UiState

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val composeView: ComposeView = findViewById(R.id.composeView)
        composeView.setContent {
            val uiController = remember { AndroidUiController() }
            
            Button(onClick = {
                uiController.updateMessage("Message updated from button click!")
            }) {
                Text("Update Message")
            }

            SharedTextComponent(uiController = uiController)
        }
    }
}

Best Practices for Interoperability

• Start Small: Migrate individual UI components to Compose incrementally.
• Encapsulate Compose Views: Use ComposeView to wrap Compose UI in existing Android layouts.
• Maintain a Clear Boundary: Define clear interfaces between Compose and traditional Android Views.
• Test Thoroughly: Ensure that interoperability doesn’t introduce regressions.

Conclusion

Compose multiplatform interoperability is crucial for modern Android development. It enables the gradual adoption of Compose and the reuse of existing code, including code shared with Kotlin Multiplatform. By strategically integrating Compose with traditional Android Views and adopting best practices, developers can leverage the benefits of both frameworks, creating robust and maintainable applications.