rx java - android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views. (RxJava)

Question

I found many articles regarding the error I am getting, I know we can only update UI from the main thread only. Let me tell you the whole error I am getting:

E/RxEroor: The exception could not be delivered to the consumer because it has already cancelled/disposed of the flow or the exception has nowhere to go, to begin with. Further reading: https://github.com/ReactiveX/RxJava/wiki/What's-different-in-2.0#error-handling | android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

I am getting the error by using this:

  RxJavaPlugins.setErrorHandler(throwable -> {
        Log.e("RxEroor",throwable.getLocalizedMessage());
    });

I am using rxjava to observe things from a retrofit network call. Here is my call to ViewModel from fragment to fetch data.

compositeDisposable.add(songsOfCategoryViewModel.getAllSongs(1)
            .subscribeOn(AndroidSchedulers.mainThread())
            .subscribeWith(new DisposableSingleObserver<ServerResponse<JsonObject>>() {
                @Override
                public void onSuccess(@io.reactivex.rxjava3.annotations.NonNull ServerResponse<JsonObject> jsonObjectServerResponse) {

                    if (jsonObjectServerResponse.isStatus()){
                        Log.i("Songs Of Category",jsonObjectServerResponse.getData().toString());
                        List<SongModel> serverSongList = new Gson()
                                .fromJson(jsonObjectServerResponse.getData().get("songs")
                                        .getAsJsonArray(),new TypeToken<List<SongModel>>(){}.getType());

                        localSongList.addAll(serverSongList);
                        songAdapter.notifyDataSetChanged();
                      /*  Observable
                                .fromIterable(serverSongList)
                                .observeOn(Schedulers.io())
                                .subscribeOn(AndroidSchedulers.mainThread())
                                .subscribe(new DisposableObserver<SongModel>() {
                                    @Override
                                    public void onNext(@io.reactivex.rxjava3.annotations.NonNull SongModel songModel) {
                                        Log.i("Song",songModel.getTitle());
                                        localSongList.add(songModel);
                                        songAdapter.notifyDataSetChanged();

                                    }

                                    @Override
                                    public void onError(@io.reactivex.rxjava3.annotations.NonNull Throwable e) {

                                    }

                                    @Override
                                    public void onComplete() {
                                        Log.i("onComplete","Called");

                                    }
                                });
                        */

                    }else {
                        Log.e("Error",jsonObjectServerResponse.getMessage());
                    }
                }

                @Override
                public void onError(@io.reactivex.rxjava3.annotations.NonNull Throwable e) {
                    Log.e("Error",e.getMessage());

                }
            }));

As you can see I have provided AndroidSchedulers.mainThread() to subscribeOn. I m getting the data on onSucces method but recyclerview adapter not updating it on UI.

And let me tell you most tricky part: if I switch the app to the foreground by locking the screen or pressing the home button and return to the app, my UI get updated with the data which I have received.

Answer 1

You should be using observeOn(AndroidSchedulers.mainThread()) not subscribeOn(AndroidSchedulers.mainThread()) . Use as

.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())

subscribeOn used to specify the Scheduler on which an Observable will operate. In your case it will be an IO scheduler.

ObserveOn is used specify the Scheduler on which an observer will observe this Observable i.e the completion in this case it will be Main thread