Develop Reference

Android paging works not as expected

I tried to use paging in my project. Unfortunately, it works not as I expected. I expected that the liveDataObserver will work after callBack.onResult.But in fact, the liveDataObserver observes immediately when the loadInitial finished.The callBack works later, and didn't post data to the observer.
The code:
First I wrote a class extend PageKeyedDataSource and interface SingleCreator
public class MyPagingDataSource<T> extends PageKeyedDataSource<Integer, T>
public interface SingleCreator<T> {
SingleSubscribeProxy<Page<T>> createSingle(int page, int pageSize);
}
Then the constructor of MyPagingDataSource:
public MyPagingDataSource(SingleCreator<T> singleCreator) {
this.singleCreator = singleCreator;
}
And override loadInitial:
#Override
public void loadInitial(#NonNull LoadInitialParams<Integer> params, #NonNull LoadInitialCallback<Integer, T> callback) {
singleCreator.createSingle(1, params.requestedLoadSize)
.subscribe(new SingleObserver<Page<T>>() {
#Override
public void onSubscribe(Disposable d) {
}
#Override
public void onSuccess(Page<T> ts) {
callback.onResult(ts.list, ts.pageNumber, ts.total, ts.pageNumber - 1, ts.pageNumber + 1);
Timber.d("registerLiveData" + ts.list.size());
}
#Override
public void onError(Throwable e) {
e.printStackTrace();
}
});
try {
//when I add this, observer will work after callback
//And if not observer works before callback.onResult
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
Then the datasourceFactory is just newInstanced in viewModel:
public LiveData<PagedList<MyData>> page = loadPageData();
public LiveData<PagedList<MyData>> loadPageData() {
return new LivePagedListBuilder<>(new DataSource.Factory<Integer, MyData>() {
#Override
public DataSource<Integer, MyData> create() {
return new HBPagingDataSource<>((page, pageSize) -> loadPageSingle(page, pageSize));
}
}, 2).build();
}
the single
private SingleSubscribeProxy<Page<MyData>> loadPageSingle(int pageNum, int pageSize) {
return mModel.loadMyDates(pageNum, pageSize)
.doOnError(Throwable::printStackTrace)
.as(autoDisposable(this));
}
at fragment
mViewModel.page.observe(this, myDatas -> {
Timber.d("registerLiveData%s", myDatas.size());
myAdapter.submitList(myDatas);
});
Maybe related things:
I wrote subscribeOn and observeOn in retrofit's callAdapter
The viewModel is a scopeProvider since I'm using autoDispose
I tried some example in github. And it seems, the setValue for pageLivedata is always work after loadInitial. In this case, how can I use single?

It's seems solved.
The error is because schedule the thread using rxjava.
It makes single and datasource work in different thread.
In this case, callback onResult run after the observer.
So, I updated the callAdapter where I wrote subscribeOn and observeOn for single.
Filter by className when It's Page class, it won't do subscribeOn and observeOn.
Now the conclusion is, let paging handle the thread.

Rxjava + Realm access from incorrect thread

I'm getting this exception reading/writing from Realm
06-19 09:49:26.352 11404-11404/****** E/ContentValues: loadData: OnError Realm access from incorrect thread. Realm objects can only be accessed on the thread they were created.
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:385)
at io.realm.RealmResults.isLoaded(RealmResults.java:115)
at io.realm.OrderedRealmCollectionImpl.size(OrderedRealmCollectionImpl.java:307)
at io.realm.RealmResults.size(RealmResults.java:60)
at java.util.AbstractCollection.isEmpty(AbstractCollection.java:86)
at /****** .lambda$loadData$0(SplashPresenter.java:42)
at /****** $$Lambda$1.test(Unknown Source)
at io.reactivex.internal.operators.observable.ObservableFilter$FilterObserver.onNext(ObservableFilter.java:45)
at io.reactivex.observers.SerializedObserver.onNext(SerializedObserver.java:111)
at io.reactivex.internal.operators.observable.ObservableDelay$DelayObserver$1.run(ObservableDelay.java:84)
at io.reactivex.internal.schedulers.ScheduledRunnable.run(ScheduledRunnable.java:59)
at io.reactivex.internal.schedulers.ScheduledRunnable.call(ScheduledRunnable.java:51)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:272)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
at java.lang.Thread.run(Thread.java:761)
This is the code:
mSubscribe = Observable.just(readData())
.delay(DELAY, TimeUnit.SECONDS)
.filter(value -> !value.isEmpty())
.switchIfEmpty(createRequest())
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread()).subscribe(data -> {
getView().hideLoading();
writeData(data);
},
(throwable -> {
}));
Read data
private List<CategoryModel> readData() {
Realm defaultInstance = Realm.getDefaultInstance();
List<CategoryModel> title = defaultInstance.where(CategoryModel.class).findAllSorted("title");
defaultInstance.close();
return title;
}
Write data
private void writeData(List<CategoryModel> categoryModels) {
try {
Realm defaultInstance = Realm.getDefaultInstance();
defaultInstance.executeTransactionAsync(realm -> realm.insertOrUpdate(categoryModels));
defaultInstance.close();
} finally {
getView().notifyActivity(categoryModels);
}
}
How can I follow this logic using the proper threads?

The only rule to using Realm across threads is to remember that Realm, RealmObject or RealmResults instances cannot be passed across threads.
When you want to access the same data from a different thread, you should simply obtain a new Realm instance (i.e. Realm.getDefaultInstance()) and get your objects through a query (then close Realm at the end of the thread).
The objects will map to the same data on disk, and will be readable & writeable from any thread! You can also run your code on a background thread using realm.executeTransactionAsync() like this
.

How can i follow this logic using the proper threads?
By not trying to read on Schedulers.io() for your UI thread (Realm gives auto-updating lazy-loaded proxy views that provide change notifications for your data on the UI thread, after all).
So instead of this
mSubscribe = Observable.just(readData())
.delay(DELAY, TimeUnit.SECONDS)
.filter(value -> !value.isEmpty())
.switchIfEmpty(createRequest())
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread()).subscribe(data -> {
getView().hideLoading();
writeData(data);
},
(throwable -> {
}));
private List<CategoryModel> readData() {
Realm defaultInstance = Realm.getDefaultInstance();
List<CategoryModel> title = defaultInstance.where(CategoryModel.class).findAllSorted("title");
defaultInstance.close();
return title;
}
private void writeData(List<CategoryModel> categoryModels) {
try {
Realm defaultInstance = Realm.getDefaultInstance();
defaultInstance.executeTransactionAsync(realm -> realm.insertOrUpdate(categoryModels));
defaultInstance.close();
} finally {
getView().notifyActivity(categoryModels);
}
}
You're supposed to have something like
private Observable<List<CategoryModel>> readData() { // Flowable with LATEST might be better.
return io.reactivex.Observable.create(new ObservableOnSubscribe<List<CategoryModel>>() {
#Override
public void subscribe(ObservableEmitter<List<CategoryModel>> emitter)
throws Exception {
final Realm observableRealm = Realm.getDefaultInstance();
final RealmResults<CategoryModel> results = observableRealm.where(CategoryModel.class).findAllSortedAsync("title");
final RealmChangeListener<RealmResults<CategoryModel>> listener = results -> {
if(!emitter.isDisposed() && results.isLoaded()) {
emitter.onNext(results);
}
};
emitter.setDisposable(Disposables.fromRunnable(() -> {
if(results.isValid()) {
results.removeChangeListener(listener);
}
observableRealm.close();
}));
results.addChangeListener(listener);
}
}).subscribeOn(AndroidSchedulers.mainThread())
.unsubscribeOn(AndroidSchedulers.mainThread());
}
private void setSubscription() {
mSubscribe = readData()
.doOnNext((list) -> {
if(list.isEmpty()) {
Single.fromCallable(() -> this::createRequest)
.subscribeOn(Schedulers.io())
.subscribe((data) -> {
writeData(data);
});
}
}).subscribe(data -> {
if(!data.isEmpty()) {
getView().hideLoading();
getView().notifyActivity(data);
}
}, throwable -> {
throwable.printStackTrace();
});
}
private void writeData(List<CategoryModel> categoryModels) {
try(Realm r = Realm.getDefaultInstance()) {
r.executeTransaction(realm -> realm.insertOrUpdate(categoryModels));
}
}
void unsubscribe() {
mSubscribe.dispose();
mSubscribe = null;
}
This way (if I didn't mess anything up), you end up with the reactive data layer described here and here, except without the additional overhead of mapping out the entire results.
EDIT:
Since Realm 4.0, it is possible to expose a RealmResults directly as a Flowable (on the UI thread, or background looper thread).
public Flowable<List<MyObject>> getLiveResults() {
try(Realm realm = Realm.getDefaultInstance()) {
return realm.where(MyObject.class)
.findAllAsync()
.asFlowable()
.filter(RealmResults::isLoaded);
}
}

You need to extract required data from realm objects into POJO and emit POJOs using map operator, so that view objects can updated with data from realm using pojo on android main thread.

You can only manipulate Realm objects in a transaction or only in the thread you read/write these objects. In your case you are getting a RealmResult from the readData method and using RxJava you are switching threads which caused the exception. Use copyFromRealm to get the data from realm which will return them as plain objects rather than realm objects.

Realm accessed from incorrect thread, with Dagger

I am currently learning Dagger, RxJava, Realm and MVP in a simple project.
Basically what this app can do is it can view, add, delete and update data from database, which I'm using Realm.
I have decided to follow MVP architecture and applied repository pattern as well for data manipulation at the back end layer.
For an extra learning, I added Dagger for the dependency injection in the architecture.
Before this, I have developed an app without applying MVP nor repository pattern, not even Dagger and RxJava in mind. All seems to work well without any errors from Realm threading system. Maybe because I tied everything in a single class.
So, now that I'm moving away from that approach, I'm now having trouble implementing it in the new approach, which I think is more loosely coupled and should be better if implemented correctly.
Enough of introduction, let's get back to the topic.
The issue I'm facing right now is Realm always giving me this error:
Exception has been thrown: Realm accessed from incorrect thread.
I was suspecting that my Dagger graph isn't properly managed (especially on providing Realm instance), thus whenever I make query for data, it gives me the error.
So, my Dagger component looks like this:
#Singleton
#Component(modules = {ContextModule.class, RepositoryModule.class, PresenterModule.class})
public interface AppComponent {
/* Inejct application */
void inject(FourdoApp fourdoApp);
/* Realm Helper */
void inject(DatabaseRealm databaseRealm);
/* Activity */
void inject(MainActivity mainActivity);
void inject(TaskDetailActivity taskDetailActivity);
/* Presenter*/
void inject(MainPresenter mainPresenter);
void inject(TaskDetailPresenter taskDetailPresenter);
/* Model repository*/
void inject(TaskRepositoryImpl taskRepository);
}
Inside RepositoryModule.class;
#Module
public class RepositoryModule {
#Provides
#Singleton
Repository<Task> provideTaskRepository() {
return new TaskRepositoryImpl();
}
// Here I provide DatabaseRealm class instance
#Provides
#Singleton
public DatabaseRealm provideDatabaseRealm() {
return new DatabaseRealm();
}
}
Not sure whether I did this correctly or not. You can view the source for DI here.
For the data request to happen, inside MainActivity, I injected MainPresenter and call onRequestData interface to request it from the Presenter. From there, Presenter will make the call to Repository for the said data.
public class MainActivity extends BaseActivity implements MainContract.View {
#Inject
MainPresenter mainPresenter;
// ...
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Injecting MainActivity class
Injector.getAppComponent().inject(this);
mainPresenter.attachView(this);
// Requesting for data from Presenter
mainPresenter.onRequestData();
}
// ...
#Override
public void onRequestDataSuccess(List<String> taskList) {
doAdapter.addAll(taskList);
doAdapter.notifyDataSetChanged();
}
}
Inside MainPresenter, I injected Repository interface to make request from TaskRepositoryImpl for the real data from database.
public class MainPresenter extends BasePresenter<MainContract.View> implements MainContract.Presenter {
#Inject
Repository<Task> taskRepository;
public MainPresenter() {
Injector.getAppComponent().inject(this);
}
#Override
public void onRequestData() {
requestData();
}
private void requestData() {
taskRepository.findAll()
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(Schedulers.io())
.map(this::mapToStringList)
.subscribe(new Observer<List<String>>() {
#Override
public void onNext(List<String> strings) { // Error in this line
if (strings.size() > 0) {
mView.onRequestDataSuccess(strings);
} else {
mView.showEmpty();
}
}
});
}
}
Inside TaskRepositoryImpl, here is how I did the findAll and it should return data from DatabaseRealm:
#Override
public Observable<List<Task>> findAll() {
return Observable.create(subscriber -> {
try {
List<Task> models = databaseRealm.findAll(Task.class);
subscriber.onNext(models);
subscriber.onComplete();
} catch (Exception e) {
subscriber.onError(e);
}
});
}
Code for DatabaseRealm are as follows:
public class DatabaseRealm {
#Inject
Context context;
RealmConfiguration realmConfiguration;
public DatabaseRealm() {
Injector.getAppComponent().inject(this);
}
public void setup() {
if (realmConfiguration == null) {
Realm.init(context);
realmConfiguration = new RealmConfiguration.Builder()
.deleteRealmIfMigrationNeeded()
.build();
Realm.setDefaultConfiguration(realmConfiguration);
} else {
throw new IllegalStateException("Realm already configured");
}
}
public Realm getRealmInstance() {
return Realm.getDefaultInstance();
}
public <T extends RealmObject> T add(T model) {
Realm realm = getRealmInstance();
realm.beginTransaction();
realm.copyToRealm(model);
realm.commitTransaction();
return model;
}
public <T extends RealmObject> T update(T model) {
Realm realm = getRealmInstance();
realm.beginTransaction();
realm.copyToRealmOrUpdate(model);
realm.commitTransaction();
return model;
}
public <T extends RealmObject> T remove(T model) {
Realm realm = getRealmInstance();
realm.beginTransaction();
realm.copyToRealm(model);
realm.deleteAll();
realm.commitTransaction();
return model;
}
public <T extends RealmObject> List<T> findAll(Class<T> clazz) {
return getRealmInstance().where(clazz).findAll();
}
public void close() {
getRealmInstance().close();
}
}
Full source code for this flawed code is right here.
I'd like to make it clear that I have limited knowledge on Realm instances being used in Dagger.
I followed this tutorial for the Repository Design Pattern with Realm, but it doesn't include Dagger for its dependency injection.
Can someone guide me on why it is always telling I'm calling Realm from incorrect thread?

I think you get this error because of this:
#Override
public Observable<List<Task>> findAll() {
return Observable.create(subscriber -> {
try {
List<Task> models = databaseRealm.findAll(Task.class);
subscriber.onNext(models);
subscriber.onComplete();
} catch (Exception e) {
subscriber.onError(e);
}
});
}
You are subscribing to io Thread but you inject your databaseRealm in Main Thread.
if you get instance in your observable's create you'll not get this error.
#Override
public Observable<List<Task>> findAll() {
return Observable.create(subscriber -> {
try {
Realm realm = getRealmInstance();
List<Task> models = realm.findAll(Task.class);
subscriber.onNext(models);
subscriber.onComplete();
} catch (Exception e) {
subscriber.onError(e);
}
});
}

You need to setup RealmConfigration only once in the Application class and use the Realm.getDeafultInstance() method to access Realm Database
With Dagger you need to Pass only realm instance in constructor
You can follow this Example and fork it
Its not exactly the same code you posted here.But it might help to understand dagger better with MVP ,RxJava and Realm

Android, Retrofit , & RxJava: "Realm access from incorrect thread"

I have a realm object stored locally that I need to change > then upload to my backend. So inside userService.updateUser() I get my current user object by calling: Realm realm = Realm.getDefaultInstance() and passing that User object on to my retrofit2 call, but I get the Realm error:
Realm access from incorrect thread. Realm objects can only be accessed on the thread they were created.
So I'm subscribing on Schedulers.newThread() and observing on AndroidSchedulers.mainThread() so I'm thinking thats why the error is thrown...how can I avoid this issue?
mCompositeDisposable.add( userService.updateUser()
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribeWith(new DisposableObserver<User>(){
#Override
public void onNext(User user) {
if(mProgressDlg != null) mProgressDlg.dismiss();
}
#Override
public void onError(Throwable t) {
if(mProgressDlg != null) mProgressDlg.dismiss();
alertDlg.showIt(mResources.getString(R.string.err_saving_profile),
stringFormatter.getApiErrorMsg(t), "",
"", mParentActivity, JAlertDialog.POSITIVE,null);
}
#Override
public void onComplete() { }
}));

This works:
mCompositeDisposable.add( userService.updateUser( Realm.getDefaultInstance().copyFromRealm(mUser) )
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribeWith
...

Verify mock interactions within anonymous inner class

I am trying to test my ViewModel in my application, here is the constructor:
#Inject
public SearchUserViewModel(#Named("searchUser") UseCase searchUserUseCase) {
this.searchUserUseCase = searchUserUseCase;
}
In my test I create a SearchUserUseCase with mocks like this:
Observable error = Observable.error(new Throwable("Error"));
when(gitHubService.searchUser(MockFactory.TEST_USERNAME_ERROR)).thenReturn(error);
when(ObserverThread.getScheduler()).thenReturn(Schedulers.immediate());
when(SubscriberThread.getScheduler()).thenReturn(Schedulers.immediate());
searchUserUseCase = new SearchUserUseCase(gitHubService, SubscriberThread, ObserverThread);
In my ViewModel class I have this snippet which I want to test:
public void onClickSearch(View view) {
loadUsers();
}
private void loadUsers() {
if (username == null) {
fragmentListener.showMessage("Enter a username");
} else {
showProgressIndicator(true);
searchUserUseCase.execute(new SearchUserSubscriber(), username);
}
}
private final class SearchUserSubscriber extends DefaultSubscriber<SearchResponse> {
#Override
public void onCompleted() {
showProgressIndicator(false);
}
#Override
public void onError(Throwable e) {
showProgressIndicator(false);
fragmentListener.showMessage("Error loading users");
}
#Override
public void onNext(SearchResponse searchResponse) {
List<User> users = searchResponse.getUsers();
if (users.isEmpty()) {
fragmentListener.showMessage("No users found");
} else {
fragmentListener.addUsers(users);
}
}
}
Finally in my test I have this:
#Test
public void shouldDisplayErrorMessageIfErrorWhenLoadingUsers() {
SearchUserViewModel searchUserViewModel = new SearchUserViewModel(searchUserUseCase);
searchUserViewModel.setFragmentListener(mockFragmentListener);
searchUserViewModel.setUsername(MockFactory.TEST_USERNAME_ERROR);
searchUserViewModel.onClickSearch(view);
verify(mockFragmentListener).showMessage("Error loading users");
}
I get this error from Mockito:
Wanted but not invoked:
fragmentListener.showMessage(
"Error loading users"
);
I am not sure if this is a good test, but I somehow want to test the SearchUserSubscriber one way or another. Thanks
Edit: I have found similar questions to this problem here: Can't verify mock method call from RxJava Subscriber (which still isn't answered) and here: Verify interactions in rxjava subscribers. The latter question is similar but does not execute the subscriber in a separate class (which happens in SearchUserUseCase here).
I also tried RobolectricGradleTestRunner instead of MockitoJunitRunner and changed to Schedulers.io() and AndroidSchedulers.mainThread(), but I still get the same error.
Tried mocking SearchUserUseCase instead of GitHubService (which feels cleaner), but I'm not sure on how to test the subscriber that way since that is passed as an argument to the void method execute() in UseCase.
public void execute(Subscriber useCaseSubscriber, String query) {
subscription = buildUseCase(query)
.observeOn(postExecutionThread.getScheduler())
.subscribeOn(threadExecutor.getScheduler())
.subscribe(useCaseSubscriber);
}
And buildUseCase()
#Override
public Observable buildUseCase(String username) throws NullPointerException {
if (username == null) {
throw new NullPointerException("Query must not be null");
}
return getGitHubService().searchUser(username);
}

For me it worked out to add a Observable.Transformer<T, T> as followed:
void gatherData() {
service.doSomeMagic()
.compose(getSchedulerTransformer())
.subscribe(view::displayValue);
}
private <T> Observable.Transformer<T, T> getSchedulerTransformer() {
if (mTransformer == null) {
mTransformer = (Observable.Transformer<T, T>) observable -> observable.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
return mTransformer;
}
void setSchedulerTransformer(Observable.Transformer<Observable<?>, Observable<?>> transformer) {
mTransformer = transformer;
}
And to set the Transformer. I just passed this:
setSchedulerTransformer(observable -> {
if (observable instanceof Observable) {
Observable observable1 = (Observable) observable;
return observable1.subscribeOn(Schedulers.immediate())
.observeOn(Schedulers.immediate());
}
return null;
});
So just add a #Before method in your test and call presenter.setSchedulerTransformer and it should be able to test this. If you want more detail check this answer.

If you are using Mockito, you can probably get hold of a SearchUserSubscriber using an ArgumentCaptor, for example...
#Captor
private ArgumentCaptor<SearchUserSubscriber> subscriberCaptor;
private SearchUserSubscriber getSearchUserSubscriber() {
// TODO: ...set up the view model...
...
// Execute the code under test (making sure the line 'searchUserUseCase.execute(new SearchUserSubscriber(), username);' gets hit...)
viewModel.onClickSearch(view);
verify(searchUserUseCase).execute(subscriberCaptor.capture(), any(String.class));
return subscriberCaptor.getValue();
}
Now you can have test cases such as...
#Test
public void shouldDoSomethingWithTheSubscriber() {
SearchUserSubscriber subscriber = getSearchUserSubscriber();
...
}