How to create a background thread with a looper

HandlerThread does the job.

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

this is an example of Thread with Looper:

public class GameLoop extends Thread {@Overridepublic void run() {    super.run();    Looper.prepare(); // at first write this line of code    //do something    Looper.loop(); //and at the end write this line}

}

This seems to be working for me

public class MainScopeListener        extends Fragment {    Realm realm;    HandlerThread handlerThread;    Scheduler looperScheduler;    Observable<Realm> realmObservable;    Subscription realmSubscription;    Handler handler = new Handler(Looper.getMainLooper());    public MainScopeListener() {        setRetainInstance(true);        realm = Realm.getDefaultInstance();        Injector.INSTANCE.initializeComponent(realm);        handlerThread = new HandlerThread("REALM_LOOPER") {            @Override            protected void onLooperPrepared() {                super.onLooperPrepared();                Log.i(getName(), "ON LOOPER PREPARED");                handler.post(() -> {                    looperScheduler = AndroidSchedulers.from(handlerThread.getLooper());                    realmObservable = Observable.create(new Observable.OnSubscribe<Realm>() {                        @Override                        public void call(Subscriber<? super Realm> subscriber) {                            final Realm observableRealm = Realm.getDefaultInstance();                            observableRealm.setAutoRefresh(true);                            final RealmChangeListener<Realm> listener = realm1 -> {                                if (!subscriber.isUnsubscribed()) {                                    subscriber.onNext(observableRealm);                                }                            };                            subscriber.add(Subscriptions.create(() -> {                                observableRealm.removeChangeListener(listener);                                observableRealm.setAutoRefresh(false);                                observableRealm.close();                            }));                            observableRealm.addChangeListener(listener);                            // Immediately call onNext with the current value, as due to Realm's auto-update, it will be the latest                            // value.                            subscriber.onNext(observableRealm);                        }                    });                    realmSubscription = realmObservable.unsubscribeOn(looperScheduler).subscribeOn(looperScheduler).subscribe(realm12 -> {                        Log.i("REALM SUBSCRIPTION", "An event occurred on background thread!");                    });                });            }        };        handlerThread.start();    }    public void configureRealmHolder(MainActivity.RealmHolder realmHolder) {        realmHolder.realm = this.realm;    }    @Override    public void onDestroy() {        if(realmSubscription != null && !realmSubscription.isUnsubscribed() ) {            realmSubscription.unsubscribe();        }        handlerThread.quit();        realm.close();        super.onDestroy();    }}

and

@SuppressWarnings("NewApi")private Subscription writePeriodic() {    return Observable.interval(2000, TimeUnit.MILLISECONDS, AndroidSchedulers.mainThread()) //            .takeWhile(aLong -> counter < DogNames.values().length) //            .observeOn(Schedulers.io())            .doOnNext(aLong -> {                try(Realm bgRealm = Realm.getDefaultInstance()) {                    bgRealm.executeTransaction(realm1 -> {                        long currentIndex = realm1.where(Dog.class).max(Dog.Fields.ID.getField()).longValue();                        Dog dog = new Dog();                        dog.setId(currentIndex + 1);                        dog.setName(DogNames.values()[((Long) dog.getId()).intValue() % DogNames.values().length].name());                        dog = realm1.copyToRealmOrUpdate(dog);                        Log.i(TAG, "Realm write successful [" + counter + "] :: [" + dog.getName() + "].");                        counter++;                    });                }            }).subscribe();}

Results in

01-21 00:58:51.672 2094-2127/com.zhuinden.rxrealm I/DogView: Realm write successful [1] :: [Munch].01-21 00:58:51.672 2094-2115/com.zhuinden.rxrealm I/REALM SUBSCRIPTION: An event occurred on background thread!

So the HandlerThread Realm is able to receive automatic updates.

Copying from the Realm still results in eager evaluation of results, so it is not an efficient way of handling large data sets.