Speech-to-text and Text-to-speech with Android

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical"
    android:padding="24dp"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btn_stt"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Speak" />

    <EditText
        android:id="@+id/et_text_input"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_marginTop="24dp"
        android:layout_marginBottom="24dp"
        android:layout_weight="1"
        android:gravity="center"
        android:hint="Text from STT or for TTS goes here." />

    <Button
        android:id="@+id/btn_tts"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Listen" />

</LinearLayout>

    companion object {
        private const val REQUEST_CODE_STT = 1
    }

    btn_stt.setOnClickListener {
        // Get the Intent action
        val sttIntent = Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH)
        // Language model defines the purpose, there are special models for other use cases, like search.
        sttIntent.putExtra(RecognizerIntent.EXTRA_LANGUAGE_MODEL, RecognizerIntent.LANGUAGE_MODEL_FREE_FORM)
        // Adding an extra language, you can use any language from the Locale class.
        sttIntent.putExtra(RecognizerIntent.EXTRA_LANGUAGE, Locale.getDefault())
        // Text that shows up on the Speech input prompt.
        sttIntent.putExtra(RecognizerIntent.EXTRA_PROMPT, "Speak now!")
        try {
            // Start the intent for a result, and pass in our request code.
            startActivityForResult(sttIntent, REQUEST_CODE_STT)
        } catch (e: ActivityNotFoundException) {
            // Handling error when the service is not available.
            e.printStackTrace()
            Toast.makeText(this, "Your device does not support STT.", Toast.LENGTH_LONG).show()
        }
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        when (requestCode) {
            // Handle the result for our request code.
            REQUEST_CODE_STT -> {
                // Safety checks to ensure data is available.
                if (resultCode == Activity.RESULT_OK && data != null) {
                    // Retrieve the result array.
                    val result = data.getStringArrayListExtra(RecognizerIntent.EXTRA_RESULTS)
                    // Ensure result array is not null or empty to avoid errors.
                    if (!result.isNullOrEmpty()) {
                        // Recognized text is in the first position.
                        val recognizedText = result[0]
                        // Do what you want with the recognized text.
                        et_text_input.setText(recognizedText)
                    }
                }
            }
        }
    }

    private val textToSpeechEngine: TextToSpeech by lazy {
        // Pass in context and the listener.
        TextToSpeech(this,
            TextToSpeech.OnInitListener { status ->
                // set our locale only if init was success.
                if (status == TextToSpeech.SUCCESS) {
                    textToSpeechEngine.language = Locale.UK
                }
            })
    }

btn_tts.setOnClickListener {
    // Get the text to be converted to speech from our EditText.
    val text = et_text_input.text.toString().trim()
    // Check if user hasn't input any text.
    if (text.isNotEmpty()) {
        // Lollipop and above requires an additional ID to be passed.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            // Call Lollipop+ function
            textToSpeechEngine.speak(text, TextToSpeech.QUEUE_FLUSH, null, "tts1")
        } else {
            // Call Legacy function
            textToSpeechEngine.speak(text, TextToSpeech.QUEUE_FLUSH, null)
        }
    } else {
        Toast.makeText(this, "Text cannot be empty", Toast.LENGTH_LONG).show()
    }
}

override fun onPause() {
    textToSpeechEngine.stop()
    super.onPause()
}

override fun onDestroy() {
    textToSpeechEngine.shutdown()
    super.onDestroy()
}