Using Kotlin in a .NET MAUI App (Android)

 To use Android native Kotlin code in a .NET MAUI app, you need to bridge between the two worlds—.NET (C#) and the Android Java/Kotlin world. In .NET MAUI, this is possible on Android using the Java Native Interface (JNI) or by creating a Java/Kotlin library (AAR) and binding it via a Binding Library.

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Example: Using Kotlin in a .NET MAUI App (Android)

Goal: Call a Kotlin function from a .NET MAUI app on Android.

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Step 1: Create a Kotlin Library (AAR)

Use Android Studio to create a Kotlin library:

MyKotlinLibrary.kt

package com.example.mykotlinlib

class MyKotlinHelper {
    fun greet(name: String): String {
        return "Hello from Kotlin, $name!"
    }
}

Build the AAR:

• Go to Build > Make Module 'mykotlinlibrary'.

• The AAR file is located in build/outputs/aar/mykotlinlibrary-release.aar.

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Step 2: Create a .NET MAUI Android Binding Library

In your MAUI solution:

1. Right-click on the solution → Add > New Project.

2. Choose Android Bindings Library.

3. Name it something like MyKotlinBinding.

Add the AAR file:

• Add the AAR to the Jars folder (create it if needed).

• Right-click → Build Action → LibraryProjectZip.

Example Directory:

MyKotlinBinding/
└── Jars/
    └── mykotlinlibrary-release.aar

Now build the binding project. It will auto-generate C# bindings to the Kotlin class.

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Step 3: Use the Kotlin Code in Your .NET MAUI App

In your .NET MAUI app project:

• Add a project reference to the MyKotlinBinding library.

Then, you can access the Kotlin class:

Example: MainPage.xaml.cs

#if ANDROID
using Com.Example.Mykotlinlib; // Namespace auto-generated from the Kotlin AAR
#endif

...

public partial class MainPage : ContentPage
{
    public MainPage()
    {
        InitializeComponent();

#if ANDROID
        var helper = new MyKotlinHelper();
        string message = helper.Greet("MAUI Developer");
        Console.WriteLine(message); // Output: Hello from Kotlin, MAUI Developer!
#endif
    }
}

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Output

On Android, when you run the app, you'll see in the logs or debugger:

Hello from Kotlin, MAUI Developer!

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🔧 Notes

• The Kotlin class must be public, and its methods should not be inline or internal.

• If the Kotlin code uses Kotlin-only features like coroutines or default parameters, you may need extra configuration in your binding project.