checkNL.java

String enabledNotificationListeners = Settings.Secure.getString(context.getContentResolver(), "enabled_notification_listeners");

// check to see if the enabledNotificationListeners String contains our package name
if (enabledNotificationListeners == null || !enabledNotificationListeners.contains(context.getPackageName())) {
    // in this situation we know that the user has not granted the app the Notification access permission
    throw new Exception();
} else {
    doSomethingThatRequiresNotificationAccessPermission();
}