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

Question

I am trying to combine retrofit 2 with RxJava and Realm, by saving the response of the service call returned by the retrofit observable to local database using realm. So i get an exception saying that Realm access from incorrect thread. Here is my code :

Trail 1:

restApi.userEntityList()
            .map(userEntityDataMapper::transformAllToRealm)
            .doOnNext(userRealmModels -> {
                if (userRealmModels != null){
                    mRealm = Realm.getInstance(mContext);
                    mRealm.asObservable()
                            .map(realm -> mRealm.copyToRealmOrUpdate(userEntity))
                            .subscribe(new Subscriber<Object>() {
                                @Override
                                public void onCompleted() {

                                }

                                @Override
                                public void onError(Throwable e) {
                                    e.printStackTrace();
                                }

                                @Override
                                public void onNext(Object o) {
                                    Log.d("RealmManager", "user added!");
                                }
                            });
                }})
            .map(userEntityDataMapper::transformAll)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(new Subscriber<List<User>>() {
                 @Override
                 public void onCompleted() {
                     hideViewLoading();
                 }

                 @Override
                 public void onError(Throwable e) {
                     hideViewLoading();
                     showErrorMessage(new DefaultErrorBundle((Exception) e));
                     showViewRetry();
                 }

                 @Override
                 public void onNext(List<User> users) {
                     showUsersCollectionInView(users);
                 }
            });

Trail 2:

restApi.userEntityList()
            .map(userEntityDataMapper::transformAllToRealm)
            .doOnNext(userRealmModels -> {
                if (userRealmModels != null) {
                    mRealm = Realm.getInstance(mContext);
                    mRealm.beginTransaction();
                    mRealm.copyToRealmOrUpdate(userEntity);
                    mRealm.commitTransaction();
                }
            })
            .map(userEntityDataMapper::transformAll)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(new Subscriber<List<User>>() {
                 @Override
                 public void onCompleted() {
                     hideViewLoading();
                 }

                 @Override
                 public void onError(Throwable e) {
                     hideViewLoading();
                     showErrorMessage(new DefaultErrorBundle((Exception) e));
                     showViewRetry();
                 }

                 @Override
                 public void onNext(List<User> users) {
                     showUsersCollectionInView(users);
                 }
            });

Logcat :

W/System.err: java.lang.IllegalStateException: Realm access from incorrect thread. Realm objects can only be accessed on the thread they were created.
at io.realm.BaseRealm.checkIfValid(BaseRealm.java:349)
at io.realm.BaseRealm.commitTransaction(BaseRealm.java:291)
at io.realm.Realm.commitTransaction(Realm.java:108)
at com.zeyad.cleanarchitecturet.data.db.RealmManagerImpl.put(RealmManagerImpl.java:66)
at com.zeyad.cleanarchitecturet.data.db.RealmManagerImpl.putAll(RealmManagerImpl.java:91)
at com.zeyad.cleanarchitecturet.data.repository.datasource.CloudUserDataStore$2.call(CloudUserDataStore.java:36)
at com.zeyad.cleanarchitecturet.data.repository.datasource.CloudUserDataStore$2.call(CloudUserDataStore.java:32)
at rx.Observable$11.onNext(Observable.java:4445)
at rx.internal.operators.OperatorDoOnEach$1.onNext(OperatorDoOnEach.java:80)
at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:54)
at rx.internal.operators.OperatorMerge$MergeSubscriber.emitScalar(OperatorMerge.java:477)
at rx.internal.operators.OperatorMerge$MergeSubscriber.tryEmit(OperatorMerge.java:435)
at rx.internal.operators.OperatorMerge$MergeSubscriber.onNext(OperatorMerge.java:228)
at rx.internal.operators.OperatorMerge$MergeSubscriber.onNext(OperatorMerge.java:142)
at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:54)
at retrofit.RxJavaCallAdapterFactory$CallOnSubscribe.call(RxJavaCallAdapterFactory.java:113)
at retrofit.RxJavaCallAdapterFactory$CallOnSubscribe.call(RxJavaCallAdapterFactory.java:88)
at rx.Observable$2.call(Observable.java:162)
at rx.Observable$2.call(Observable.java:154)
at rx.Observable$2.call(Observable.java:162)
at rx.Observable$2.call(Observable.java:154)
at rx.Observable$2.call(Observable.java:162)
at rx.Observable$2.call(Observable.java:154)
at rx.Observable$2.call(Observable.java:162)
at rx.Observable$2.call(Observable.java:154)
at rx.Observable$2.call(Observable.java:162)
at rx.Observable$2.call(Observable.java:154)
at rx.Observable$2.call(Observable.java:162)
at rx.Observable$2.call(Observable.java:154)
at rx.Observable$2.call(Observable.java:162)
at rx.Observable$2.call(Observable.java:154)
at rx.Observable.unsafeSubscribe(Observable.java:8098)
at rx.internal.operators.OperatorSubscribeOn$1$1.call(OperatorSubscribeOn.java:62)
at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)
at rx.schedulers.ExecutorScheduler$ExecutorSchedulerWorker.run(ExecutorScheduler.java:98)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)
Caused by: rx.exceptions.OnErrorThrowable$OnNextValue: OnError while emitting onNext value: java.util.ArrayList.class
at rx.exceptions.Exceptions.throwOrReport(Exceptions.java:187)
at rx.internal.operators.OperatorDoOnEach$1.onNext(OperatorDoOnEach.java:82)
... 29 more

Answer 1

I found out how to fix it. To save server responses from retrofit 2 to realm then pass to the UI. I made retrofit return realm objects by overriding the Gson Builder like this:

Retrofit.Builder()
            .baseUrl(RestApi.API_BASE_URL)
            .client(okHttpClient)
            .callbackExecutor(new JobExecutor())
            .addConverterFactory(GsonConverterFactory.create(new GsonBuilder()
                    .setExclusionStrategies(new ExclusionStrategy() {
                        @Override
                        public boolean shouldSkipField(FieldAttributes f) {
                            return f.getDeclaringClass().equals(RealmObject.class);
                        }

                        @Override
                        public boolean shouldSkipClass(Class<?> clazz) {
                            return false;
                        }
                    }).create()))
            .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
            .build();

Then:

restApi.userRealmList()
    .doOnNext(userRealmModels -> {
        if (userRealmModels != null) {
            Realm realm = Realm.getInstance(mContext);
            realm.beginTransaction();
            realm.copyToRealmOrUpdate(userRealmModels);
            realm.commitTransaction();
            realm.close();
        }})
    .map(userEntityDataMapper::transformAll)
    .subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe(new Subscriber<List<User>>() {
         @Override
         public void onCompleted() {
             hideViewLoading();
         }

         @Override
         public void onError(Throwable e) {
             hideViewLoading();
             showErrorMessage(new DefaultErrorBundle((Exception) e));
             showViewRetry();
         }

         @Override
         public void onNext(List<User> users) {
             showUsersCollectionInView(users);
         }
    });