Asynchronous Worker in Android WorkManager

Question

Google recently announced new WorkManager architecture component. It makes it easy to schedule synchronous work by implementing doWork() in Worker class, but what if I want to do some asynchronous work in the background? For example, I want to make a network service call using Retrofit. I know I can make a synchronous network request, but it would block the thread and just feels wrong. Is there any solution for this or it is just not supported at the moment?

Answer 1

I used a countdownlatch and waited for this to reach 0, which will only happen once the asynchronous callback has updated it. See this code:

public WorkerResult doWork() {          final WorkerResult[] result = {WorkerResult.RETRY};         CountDownLatch countDownLatch = new CountDownLatch(1);         FirebaseFirestore db = FirebaseFirestore.getInstance();          db.collection("collection").whereEqualTo("this","that").get().addOnCompleteListener(task -> {             if(task.isSuccessful()) {                 task.getResult().getDocuments().get(0).getReference().update("field", "value")                         .addOnCompleteListener(task2 -> {                             if (task2.isSuccessful()) {                                 result[0] = WorkerResult.SUCCESS;                             } else {                                 result[0] = WorkerResult.RETRY;                             }                             countDownLatch.countDown();                         });             } else {                 result[0] = WorkerResult.RETRY;                 countDownLatch.countDown();             }         });          try {             countDownLatch.await();         } catch (InterruptedException e) {             e.printStackTrace();         }          return result[0];      } 

Answer 2

FYI there is now ListenableWorker, which is designed to be asynchronous.

Edit: Here are some snippets of example usage. I cut out big chunks of code that I think aren't illustrative, so there's a good chance there's a minor error or two here.

This is for a task that takes a String photoKey, retrieves metadata from a server, does some compression work, and then uploads the compressed photo. This happens off the main thread. Here's how we send the work request:

private void compressAndUploadFile(final String photoKey) {     Data inputData = new Data.Builder()             .putString(UploadWorker.ARG_PHOTO_KEY, photoKey)             .build();     Constraints constraints = new Constraints.Builder()             .setRequiredNetworkType(NetworkType.CONNECTED)             .build();     OneTimeWorkRequest request = new OneTimeWorkRequest.Builder(UploadWorker.class)             .setInputData(inputData)             .setConstraints(constraints)             .build();     WorkManager.getInstance().enqueue(request); } 

And in UploadWorker:

public class UploadWorker extends ListenableWorker {     private static final String TAG = "UploadWorker";     public static final String ARG_PHOTO_KEY = "photo-key";      private String mPhotoKey;      /**      * @param appContext   The application {@link Context}      * @param workerParams Parameters to setup the internal state of this worker      */     public UploadWorker(@NonNull Context appContext, @NonNull WorkerParameters workerParams) {         super(appContext, workerParams);         mPhotoKey = workerParams.getInputData().getString(ARG_PHOTO_KEY);     }      @NonNull     @Override     public ListenableFuture<Payload> onStartWork() {         SettableFuture<Payload> future = SettableFuture.create();         Photo photo = getPhotoMetadataFromServer(mPhotoKey).addOnCompleteListener(task -> {             if (!task.isSuccessful()) {                 Log.e(TAG, "Failed to retrieve photo metadata", task.getException());                 future.setException(task.getException());                 return;             }             MyPhotoType photo = task.getResult();             File file = photo.getFile();             Log.d(TAG, "Compressing " + photo);             MyImageUtil.compressImage(file, MyConstants.photoUploadConfig).addOnCompleteListener(compressionTask -> {                 if (!compressionTask.isSuccessful()) {                     Log.e(TAG, "Could not parse " + photo + " as an image.", compressionTask.getException());                     future.set(new Payload(Result.FAILURE));                     return;                 }                 byte[] imageData = compressionTask.getResult();                 Log.d(TAG, "Done compressing " + photo);                 UploadUtil.uploadToServer(photo, imageData);                 future.set(new Payload(Result.SUCCESS));             });         });         return future;     } } 

EDIT

Depending on the things you are using in your application, you can also extends RxWorker (if you are using RxJava) or CoroutineWorker (if you're using Coroutines). They both extend from ListenableWorker.