Native Module Android

How to Create a Native Module in Android

This detailed guide explains how to create a expo module for the Android platform within a Expo application. The process follows the step-by-step instructions from the official documentation.

1. Open the Android Project in Android Studio

You can include this in your package.json under the scripts section:

"scripts": {
    "open:android": "open -a \"Android Studio\" android"
},

This script ensures that the Expo module opens correctly in Android Studio.

2. Create the Native Module

Create a file named CafSmartAuthBridgeModule.kt in the directory modules/caf-smart-auth-react-native/android/app/src/main/java/com/your-app-name/. This file will contain the class that implements the native module.

Key Functions of the CafSmartAuthBridgeModule Class

• build: The build function is responsible for configuring and instantiating the CafSmartAuth object using the provided parameters. This function applies various settings, such as defining stages and facial authentication, to prepare the SDK for use.

• setupListener: Sets up a listener to monitor the status of verification operations, such as success, pending, error, cancellation, and others.

• requestPermission: Requests the necessary permissions, such as location permissions, for the proper functioning of the SDK.

• startSmartAuth: Exposed to JavaScript, this function starts the smart authentication process using the received parameters.

• requestLocationPermissions: Exposed to JavaScript, allows the application to request location permissions from the user.

Example Implementation of the CafSmartAuthBridgeModule.kt File

class CafSmartAuthBridgeModule : Module() {
    private val context
        get() = requireNotNull(appContext.reactContext)
    private val activity
        get() = requireNotNull(appContext.currentActivity)

    // Each module class must implement the definition function. The definition consists of components
    // that describes the module's functionality and behavior.
    // See https://docs.expo.dev/modules/module-api for more details about available components.
    override fun definition() = ModuleDefinition {
        // Sets the name of the module that JavaScript code will use to refer to the module. Takes a string as an argument.
        // Can be inferred from module's class name, but it's recommended to set it explicitly for clarity.
        // The module will be accessible from `requireNativeModule('CafSmartAuthBridgeModule')` in JavaScript.
        Name(CAF_SMART_AUTH_MODULE_NAME)

        // Defines event names that the module can send to JavaScript.
        Events(
            CAF_SMART_AUTH_SUCCESS_EVENT,
            CAF_SMART_AUTH_PENDING_EVENT,
            CAF_SMART_AUTH_ERROR_EVENT,
            CAF_SMART_AUTH_CANCEL_EVENT,
            CAF_SMART_AUTH_LOADING_EVENT,
            CAF_SMART_AUTH_LOADED_EVENT
        )

        // Defines a JavaScript synchronous function that runs the native code on the JavaScript thread.
        Function(CAF_SMART_AUTH_FUNCTION_START_SMART_AUTH) { mfaToken: String, faceAuthToken: String, personId: String, policyId: String, jsonString: String ->
            Handler(Looper.getMainLooper()).post {
                val smartAuth = build(
                    mfaToken = mfaToken,
                    faceAuthToken = faceAuthToken,
                    settings = jsonString
                )

                smartAuth.verifyPolicy(personId, policyId, setupListener())
            }
        }

        // Defines a JavaScript asynchronous function that runs the native code on the JavaScript thread.
        AsyncFunction(CAF_SMART_AUTH_FUNCTION_REQUEST_LOCATION_PERMISSIONS) {
            Handler(Looper.getMainLooper()).post {
                try {
                    requestPermission(
                        permission = Manifest.permission.ACCESS_FINE_LOCATION,
                        activity = activity
                    )
                    requestPermission(
                        permission = Manifest.permission.ACCESS_COARSE_LOCATION,
                        activity = activity
                    )
                } catch (e: Exception) {
                    throw IllegalStateException("$PERMISSION_ERROR_DESCRIPTION ${e.message}")
                }
            }
        }
    }

    private fun build(mfaToken: String, faceAuthToken: String, settings: String): CafSmartAuth {
        val faceAuthenticationSettings = CafSmartAuthBridgeSettings(settings = settings)

        return CafSmartAuth.CafBuilder(mfaToken, context)
            .apply {
                setSdkPlatform(CafSdkPlatform.REACT_NATIVE)
                faceAuthenticationSettings.cafStage?.let { setStage(it) }
                setFaceAuthenticatorSettings(
                    CafFaceAuthenticatorSettings(
                        faceAuthToken,
                        faceAuthenticationSettings.faceAuthenticatorSettings?.loadingScreen,
                        faceAuthenticationSettings.faceAuthenticatorSettings?.enableScreenCapture,
                        faceAuthenticationSettings.faceAuthenticatorSettings?.filter
                    )
                )
            }
            .build()
    }

    private fun setupListener() = object : CafVerifyPolicyListener {
        override fun onSuccess(
            isAuthorized: Boolean,
            attemptId: String?,
            attestation: String?
        ) {
            sendEvent(CAF_SMART_AUTH_SUCCESS_EVENT, mapOf(
                CAF_MAP_KEY_IS_AUTHORIZED to isAuthorized,
                CAF_MAP_KEY_ATTEMPT_ID to (attemptId ?: ""),
                CAF_MAP_KEY_ATTESTATION to (attestation ?: "")
            ))
        }

        override fun onPending(isAuthorized: Boolean, attestation: String?) {
            sendEvent(CAF_SMART_AUTH_PENDING_EVENT, mapOf(
                CAF_MAP_KEY_IS_AUTHORIZED to isAuthorized,
                CAF_MAP_KEY_ATTESTATION to (attestation ?: "")
            ))
        }

        override fun onError(failure: CafFailure) {
            sendEvent(CAF_SMART_AUTH_ERROR_EVENT, mapOf(
                CAF_MAP_KEY_ERROR_MESSAGE to failure.message
            ))
        }

        override fun onCancel() {
            sendEvent(CAF_SMART_AUTH_CANCEL_EVENT, mapOf(CAF_MAP_KEY_IS_CANCELLED to true))
        }

        override fun onLoading() {
            sendEvent(CAF_SMART_AUTH_LOADING_EVENT, mapOf(CAF_MAP_KEY_IS_LOADING to true))
        }

        override fun onLoaded() {
            sendEvent(CAF_SMART_AUTH_LOADED_EVENT, mapOf(CAF_MAP_KEY_IS_LOADED to true))
        }
    }

    private fun requestPermission(permission: String, activity: Activity) {
        if (ContextCompat.checkSelfPermission(
                context,
                permission
            ) != PackageManager.PERMISSION_GRANTED
        ) {
            ActivityCompat.requestPermissions(activity, arrayOf(permission), REQUEST_CODE)
        }
    }

    companion object {
        private const val REQUEST_CODE = 1234

        private const val CAF_SMART_AUTH_MODULE_NAME = "CafSmartAuthBridgeModule"
        private const val CAF_SMART_AUTH_FUNCTION_START_SMART_AUTH = "startSmartAuth"
        private const val CAF_SMART_AUTH_FUNCTION_REQUEST_LOCATION_PERMISSIONS = "requestLocationPermissions"

        private const val CAF_SMART_AUTH_SUCCESS_EVENT = "CafSmartAuth_Success"
        private const val CAF_SMART_AUTH_PENDING_EVENT = "CafSmartAuth_Pending"
        private const val CAF_SMART_AUTH_ERROR_EVENT = "CafSmartAuth_Error"
        private const val CAF_SMART_AUTH_CANCEL_EVENT = "CafSmartAuth_Cancel"
        private const val CAF_SMART_AUTH_LOADING_EVENT = "CafSmartAuth_Loading"
        private const val CAF_SMART_AUTH_LOADED_EVENT = "CafSmartAuth_Loaded"

        private const val CAF_MAP_KEY_IS_AUTHORIZED = "isAuthorized"
        private const val CAF_MAP_KEY_ATTEMPT_ID = "attemptId"
        private const val CAF_MAP_KEY_ATTESTATION = "attestation"
        private const val CAF_MAP_KEY_ERROR_MESSAGE = "errorMessage"
        private const val CAF_MAP_KEY_IS_CANCELLED = "isCancelled"
        private const val CAF_MAP_KEY_IS_LOADING = "isLoading"
        private const val CAF_MAP_KEY_IS_LOADED = "isLoaded"

        private const val PERMISSION_ERROR_DESCRIPTION = "Error checking location permissions:"
    }
}

3. Create the CafSmartAuthBridgeSettings.kt File

This file will handle the interpretation of data sent from React Native to the native module.

Example Implementation:

internal data class CafFaceAuthenticationSettingsModel(
    val loadingScreen: Boolean?,
    val enableScreenCapture: Boolean?,
    val filter: CafFilterStyle?
)

internal class CafSmartAuthBridgeSettings(settings: String) : Serializable {
    val cafStage: CafStage?
    val faceAuthenticatorSettings: CafFaceAuthenticationSettingsModel?

    init {
        val jsonObject = JSONObject(settings)

        cafStage = if (jsonObject.has(STAGE)) CafStage.entries[jsonObject.getInt(STAGE)]
        else null

        faceAuthenticatorSettings = if (jsonObject.has(FACE_AUTHENTICATION_SETTINGS)) {
            val faceAuthenticatorSettings = jsonObject.getJSONObject(FACE_AUTHENTICATION_SETTINGS)

            val filterStyle = if (faceAuthenticatorSettings.has(FILTER)) {
                CafFilterStyle.entries[faceAuthenticatorSettings.getInt(FILTER)]
            } else null

            CafFaceAuthenticationSettingsModel(
                faceAuthenticatorSettings.optBoolean(LOADING_SCREEN),
                faceAuthenticatorSettings.optBoolean(ENABLE_SCREEN_CAPTURE),
                filterStyle ?: CafFilterStyle.LINE_DRAWING
            )
        } else null
    }

    private companion object {
        const val STAGE = "stage"
        const val FACE_AUTHENTICATION_SETTINGS = "faceAuthenticationSettings"
        const val LOADING_SCREEN = "loadingScreen"
        const val ENABLE_SCREEN_CAPTURE = "enableScreenCapture"
        const val FILTER = "filter"
    }
}

With this, your native module is configured and ready to be used in React Native.