val builder = AlertDialog.Builder(this, R.style.AlertDialogStyle)
val inflater = this.layoutInflater
val dialogView: View = inflater.inflate(R.layout.alert_dialog_et_layout, null)

builder.apply {
    setMessage(R.string.dialog_msg)
    setPositiveButton(R.string.dialog_accept_label, null)
    setNegativeButton(R.string.dialog_close_label, null)
    setView(dialogView)
}

val alertDialog = builder.create()
val positiveBtn = alertDialog.getButton(AlertDialog.BUTTON_POSITIVE)
val negativeBtn = alertDialog.getButton(AlertDialog.BUTTON_NEGATIVE)
alertDialog.show()

positiveBtn.setOnClickListener {
    //do some stuff with data
}

negativeBtn.setOnClickListener {
    alertDialog.cancel()
}

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference