Convert AsyncTask to RxAndroid

Question

I have the following method to post response to UI using otto and AsyncTask.

private static void onGetLatestStoryCollectionSuccess(final StoryCollection storyCollection, final Bus bus) {
    new AsyncTask<Void, Void, Void>() {
        @Override
        protected Void doInBackground(Void... params) {
            bus.post(new LatestStoryCollectionResponse(storyCollection));
            return null;
        }
    }.execute();
}

I need help to convert this AsyncTask to RxJava using RxAndroid library.

Answer 1

Don't use .create() but use .defer()

Observable<File> observable = Observable.defer(new Func0<Observable<File>>() {
  @Override public Observable<File> call() {

    File file = downloadFile();

    return Observable.just(file);
  }
});

to know more details see https://speakerdeck.com/dlew/common-rxjava-mistakes

Answer 2

This is an example for a file download task using RxJava

Observable<File> downloadFileObservable() {
    return Observable.create(new OnSubscribeFunc<File>() {
        @Override
        public Subscription onSubscribe(Observer<? super File> fileObserver) {
            try {
                byte[] fileContent = downloadFile();
                File file = writeToFile(fileContent);
                fileObserver.onNext(file);
                fileObserver.onCompleted();
            } catch (Exception e) {
                fileObserver.onError(e);
            }
            return Subscriptions.empty();
        }
    });
}

Usage:

downloadFileObservable()
  .subscribeOn(Schedulers.newThread())
  .observeOn(AndroidSchedulers.mainThread())
  .subscribe(observer); // you can post your event to Otto here

This would download the file on a new thread and notify you on the main thread.

OnSubscribeFunc was deprecated. Code updated to use OnSubscribe insted. For more info see issue 802 on Github.

Code from here.

Answer 3

In your case you can use fromCallable. Less code and automatic onError emissions.

Observable<File> observable = Observable.fromCallable(new Callable<File>() {
        @Override
        public File call() throws Exception {
            File file = downloadFile();
            return file;
        }
    });

Using lambdas:

Observable<File> observable = Observable.fromCallable(() -> downloadFile());