Exploring Kotlin's Multiplatform Projects with Kotlin/Native

In this tutorial, we will explore Kotlin's multiplatform projects and how to use Kotlin/Native to create cross-platform applications. Kotlin multiplatform projects allow developers to write shared code that can be used across different platforms, such as iOS, Android, and desktop. We will cover the advantages of Kotlin multiplatform projects, setting up Kotlin/Native, writing shared code, building and running the project, interoperability between Kotlin and native code, and testing the shared code.

What are Kotlin Multiplatform Projects?

Kotlin multiplatform projects enable developers to write shared code that can be used across multiple platforms. This means that a single codebase can be shared between iOS, Android, and desktop applications, reducing code duplication and improving code maintenance. Kotlin multiplatform projects achieve this by providing a common API that can be used by platform-specific implementations.

Advantages of Kotlin Multiplatform Projects

There are several advantages to using Kotlin multiplatform projects:

1. Code Sharing: Kotlin multiplatform projects allow developers to write shared code that can be used across different platforms, reducing code duplication and improving code reuse.
2. Consistent APIs: Kotlin multiplatform projects provide a common API that can be used by platform-specific implementations, ensuring consistent behavior across different platforms.
3. Platform-specific optimizations: Kotlin multiplatform projects allow developers to write platform-specific implementations that can take advantage of platform-specific optimizations, improving performance and user experience.
4. Simplified maintenance: With a single codebase for multiple platforms, developers can make changes and updates more easily, reducing the time and effort required for maintenance.

Getting Started

Before we can start exploring Kotlin multiplatform projects, we need to set up Kotlin/Native.

Setting up Kotlin/Native

To set up Kotlin/Native, follow these steps:

1. Install Kotlin. You can download the Kotlin compiler from the official Kotlin website or use a package manager like Homebrew (for macOS) or SDKMAN (for Linux).
2. Install Kotlin/Native. Kotlin/Native is included in the Kotlin distribution, so you don't need to install anything extra.
3. Verify the installation. Open a terminal and run the following command to verify that Kotlin/Native is installed correctly:

$ kotlinc-native -version

If everything is set up correctly, you should see the Kotlin/Native version information.

Creating a Kotlin Multiplatform Project

Once Kotlin/Native is set up, we can create a Kotlin multiplatform project.

1. Create a new directory for your project and navigate to it in the terminal.
2. Run the following command to create a new Kotlin multiplatform project:

$ kotlin-native-multiplatform init

This command initializes a new Kotlin multiplatform project and creates the necessary project structure.

Sharing Code

Now that we have set up Kotlin/Native and created a Kotlin multiplatform project, let's start writing shared code that can be used across different platforms.

Writing Shared Code

Shared code in Kotlin multiplatform projects is written in Kotlin and can be used by platform-specific implementations. To write shared code, follow these steps:

1. Create a new Kotlin file in the shared module of your project.
2. Write the shared code in this file.

For example, let's create a file called "Calculator.kt" in the shared module and write a simple addition function:

// Calculator.kt

fun add(a: Int, b: Int): Int {
    return a + b
}

This code defines a function called "add" that takes two integers as parameters and returns their sum.

Platform-Specific Implementations

In addition to shared code, Kotlin multiplatform projects also allow developers to write platform-specific implementations. These implementations can use the shared code and provide platform-specific functionality.

To create platform-specific implementations, follow these steps:

1. Create a new Kotlin file in the platform-specific module for the desired platform.
2. Write the platform-specific code in this file.

For example, let's create a file called "Calculator.kt" in the Android module and write an implementation that uses the shared addition function:

// Calculator.kt (Android)

actual fun showResult(result: Int) {
    Toast.makeText(context, "Result: $result", Toast.LENGTH_SHORT).show()
}

This code defines an "actual" function called "showResult" that takes an integer as a parameter and displays a toast message on the Android platform.

Building and Running

Now that we have written shared code and platform-specific implementations, let's learn how to build and run the Kotlin multiplatform project.

Building the Project

To build the project, follow these steps:

1. Open a terminal and navigate to the root directory of the project.
2. Run the following command to build the project:

$ ./gradlew build

This command builds the project and generates the necessary artifacts for each platform.

Running the Project

To run the project, follow these steps:

1. Open a terminal and navigate to the root directory of the project.
2. Run the following command to run the project:

$ ./gradlew run

This command runs the project and launches the application on the specified platform.

Interoperability

Kotlin multiplatform projects allow developers to call native code from Kotlin and vice versa. This enables seamless interoperability between Kotlin and native code.

Calling Native Code from Kotlin

To call native code from Kotlin, follow these steps:

1. Import the native code module or library into your Kotlin code.
2. Use the imported native code in your Kotlin code.

For example, let's assume we have a native library called "NativeLibrary" that provides a native function called "nativeFunction". We can call this function from Kotlin as follows:

// NativeFunction.kt

import com.example.NativeLibrary

fun callNativeFunction() {
    NativeLibrary.nativeFunction()
}

This code imports the "NativeLibrary" and calls the "nativeFunction" from Kotlin.

Calling Kotlin Code from Native

To call Kotlin code from native code, follow these steps:

1. Declare the Kotlin code as "external" or "expect" in the shared module.
2. Implement the Kotlin code in the platform-specific module.

For example, let's assume we have a shared function called "sharedFunction" that we want to call from native code. In the shared module, we can declare this function as "expect":

// SharedFunction.kt

expect fun sharedFunction()

In the Android module, we can implement this function as follows:

// SharedFunction.kt (Android)

actual fun sharedFunction() {
    // Implementation for Android
}

This code implements the "sharedFunction" in the Android module.

Testing

Testing is an important part of software development, and Kotlin multiplatform projects provide support for testing shared code as well as platform-specific testing.

Unit Testing Shared Code

To unit test shared code, follow these steps:

1. Create a new Kotlin test file in the shared module of your project.
2. Write the unit tests for the shared code in this file.

For example, let's create a file called "CalculatorTest.kt" in the shared module and write a unit test for the shared addition function:

// CalculatorTest.kt

import kotlin.test.Test
import kotlin.test.assertEquals

class CalculatorTest {
    @Test
    fun testAddition() {
        assertEquals(4, add(2, 2))
    }
}

This code defines a test class called "CalculatorTest" with a single test method called "testAddition". The test method asserts that the result of adding 2 and 2 is equal to 4.

Platform-Specific Testing

In addition to testing shared code, Kotlin multiplatform projects also allow developers to write platform-specific tests. These tests can test platform-specific functionality and ensure that the platform-specific implementations work correctly.

To create platform-specific tests, follow these steps:

1. Create a new Kotlin test file in the platform-specific module for the desired platform.
2. Write the tests for the platform-specific code in this file.

For example, let's create a file called "CalculatorTest.kt" in the Android module and write a test for the Android-specific implementation of the addition function:

// CalculatorTest.kt (Android)

import androidx.test.ext.junit.runners.AndroidJUnit4
import org.junit.runner.RunWith

@RunWith(AndroidJUnit4::class)
class CalculatorTest {
    // Tests for Android-specific functionality
}

This code sets up an AndroidJUnit4 test class for testing Android-specific functionality.

Conclusion

In this tutorial, we explored Kotlin's multiplatform projects and learned how to use Kotlin/Native to create cross-platform applications. We discussed the advantages of Kotlin multiplatform projects and how to set up Kotlin/Native. We also covered writing shared code, building and running the project, interoperability between Kotlin and native code, and testing the shared code. With Kotlin multiplatform projects, developers can write shared code that can be used across different platforms, reducing code duplication and improving code maintenance.