Realm in an Android Background Service

Question

I am using Realm in my android application.I am receiving a notification from google drive via CompletionEvent so I need to modify my realm database in a service.

The exception I get is:

java.lang.IllegalStateException: Realm access from incorrect thread. Realm objects can only be accessed on the thread they were created.

I have set my default configuration in my Application class the next way:

RealmConfiguration realmConfiguration = new RealmConfiguration.Builder(getApplicationContext())
            .deleteRealmIfMigrationNeeded()
            .build();
Realm.setDefaultConfiguration(realmConfiguration);

And in the onCreate from my service I am getting my Realm instance like this:

mRealm = Realm.getDefaultInstance();

And then I use this realm instance in the service:

mRealm.executeTransaction(realm -> {
        DocumentFileRealm documentFileRealm = realm.where(DocumentFileRealm.class)
                .equalTo("id", documentFileId)
                .findFirst();
        documentFileRealm.setDriveId(driveId);
    });

But when executing this last one the app launches the IllegalStateException. I don't know why. I am not sure if it has something to do with the way I have declared the service in my android manifest so I leave it here:

<service android:name=".package.UploadCompletionService" android:exported="true">
    <intent-filter>
        <action android:name="com.google.android.gms.drive.events.HANDLE_EVENT"/>
    </intent-filter>
</service>

Is it possible calling Realm from a background service? What is wrong with the way I am using this?

Thanks in advance.

Answer 1

In an IntentService, you're supposed to treat the onHandleIntent method like the doInBackground method of an AsyncTask.

So it runs on the background thread and you should make sure you close the Realm in a finally block.

public class PollingService extends IntentService {
    @Override
    public void onHandleIntent(Intent intent) {
        Realm realm = null;
        try {
            realm = Realm.getDefaultInstance();
            // go do some network calls/etc and get some data 
            realm.executeTransaction(new Realm.Transaction() {
                @Override
                public void execute(Realm realm) {
                     realm.createAllFromJson(Customer.class, customerApi.getCustomers()); // Save a bunch of new Customer objects
                }
            });
        } finally {
            if(realm != null) {
                realm.close();
            }
        }
    }
    // ...
}

onCreate runs on the UI thread, so your initialization of the Realm happens on a different thread, which is a no-go.