How to create a background thread with a looper

Question

Can someone please share the implementation of a background thread with a Looper that i can pass to the subscribeOn(AndroidScheduler.from(/backgroundThreadWithLooper/)).

I need this because i am trying to implement a DBService class that runs all of its operations in the background while still getting live objects updates. So when i apply an addChangeListener, an exception is thrown:

java.lang.IllegalStateException: Your Realm is opened from a thread without a Looper. Async queries need a Handler to send results of your query

or if i use findAll() instead of findAllAsync():

java.lang.IllegalStateException: You can't register a listener from a non-Looper thread or IntentService thread.

DBService code:

public Observable<List> getAll(Class clazz) {
    return Observable.defer(() -> {
        Realm realm = Realm.getDefaultInstance();
        return realm.where(clazz).findAll().asObservable()
                .map(o -> realm.copyFromRealm((RealmResults) o))
                .doOnUnsubscribe(() -> closeRealm(realm))
                .doOnTerminate(() -> closeRealm(realm));
    });
}

Answer 1

HandlerThread does the job.

HandlerThread handlerThread = new HandlerThread("backgroundThread");
if (!handlerThread.isAlive())
    handlerThread.start();
AndroidSchedulers.from(handlerThread.getLooper());