Kotlin and Java Modules

Kotlin and Java Modules

The CLI calls this backend Native Module. Use it for Android APIs and Kotlin or Java libraries. Value-returning functions use Promises in JavaScript.

Create the module using Add a Module, choosing Native Module.

File to edit

Write .kt or .java files below:

local_modules/<package>/android/src/main/java/<namespace-path>/

The starter implementation is Example.kt.

Kotlin example

package com.example.calculator

import com.example.calculator.nativemodule.annotation.SupernoteExport

class Example {
  @SupernoteExport
  fun add(left: Double, right: Double): Double = left + right
}

Java example

If you prefer Java, replace the starter with Example.java:

package com.example.calculator;

import com.example.calculator.nativemodule.annotation.SupernoteExport;

public class Example {
  public Example() {}

  @SupernoteExport
  public double add(double left, double right) {
    return left + right;
  }
}

The annotation import changes with the Android namespace selected for the module.

Call it from JavaScript

import Calculator from 'local-calculator';

const total = await Calculator.add(20, 22);

Use await for Boolean/boolean, Double/double, or String returns. Functions returning Unit or void are called without await:

@SupernoteExport
fun setEnabled(enabled: Boolean) {
  // Apply the setting.
}

Calculator.setEnabled(true);

Constructor rules

An exported concrete public class needs one of these public constructors, used in this preference order:

1. ReactApplicationContext;
2. android.content.Context;
3. no arguments.

Activity injection and arbitrary constructor parameters are not supported.

After changing exports

supernote-module validate local-calculator --build

The Android/KSP build regenerates declarations and the bridge. Add --verbose when diagnosing a failed build.

Update preserves your Kotlin and Java implementation. See Files the Generator Creates for the files Update may replace, and Export Functions for all supported signatures.