CRUD of Room in Java android, how to return the count of deleted rows from Dao and AsyncTask in Ripository through viewmodel back to CatalogActivity?

Question

I am trying to develop this small app to do CRUD operations using Room, Repository, LiveData, and ViewModel and Listview, if you want to see development of the app or commit line of Java, here in this my github repository

The original app which is called Pets at original repository of Pets is developed by using ContentProvider and ContentResolver in the subclass of SQLiteOpenHelper in Android with Java

---

the question is

Small App of android in Java to do CRUD operations by Room, Repository, LiveData, and ViewModel and Listview, how to return the count of deleted rows from Dao and AsyncTask in Repository through ViewModel back to CatalogActivity?

This is what in PetDao.java

@Query("DELETE FROM pets")
int deleteAllPets();

This is what in PetRepository.java

// this class is inside repository
    private static class DeleteAllPetsAsyncTask extends AsyncTask<Void, Void, Integer>
    {
        private PetDao petDaoOfDeleteAllAsyncTask;

        DeleteAllPetsAsyncTask(PetDao petDao)
        {
            this.petDaoOfDeleteAllAsyncTask = petDao;
        }

        @Override
        protected Integer doInBackground(Void... voids)
        {
            int countOfDeletedRows = this.petDaoOfDeleteAllAsyncTask.deleteAllPets();
            return countOfDeletedRows;
        }

        /**
         * <p>Runs on the UI thread after {@link #doInBackground}. The
         * specified result is the value returned by {@link #doInBackground}.</p>
         *
         * <p>This method won't be invoked if the task was cancelled.</p>
         *
         * @param integer The result of the operation computed by {@link #doInBackground}.
         * @see #onPreExecute
         * @see #doInBackground
         * @see #onCancelled(Object)
         */
        @Override
        protected void onPostExecute(Integer integer) {
            //super.onPostExecute(integer);
            // TODO: how to return this integer
        }
    }

    // this function is inside repository
    public void deleteAllPets()
    {
        new DeleteAllPetsAsyncTask(this.petDao).execute();
    }

This is what in PetViewModel.java

public void deleteAllPets()
{
    this.petRepository.deleteAllPets();
}

This is what in CatalogActivity.java

    private void deleteAllPets() {
        // TODO: Implement this method
        //
        Log.v(this.LOG_TAG, "rows deleted from pet database count is: ");

        this.petViewModel.deleteAllPets();
        // Show a toast message depending on whether or not the delete was successful.
        if (0 == 0) {
            // If no rows were deleted, then there was an error with the delete.
            Toast.makeText(this, super.getString(R.string.catalog_delete_all_pets_failed) +
                    " ", Toast.LENGTH_LONG).show();
        } else {
            // Otherwise, the delete was successful and we can display a toast.
            Toast.makeText(this, super.getString(R.string.catalog_delete_all_pets_successful) +
                    " ", Toast.LENGTH_LONG).show();
        }
        // Close the activity
        //super.finish();

    }

I am also expecting an answer from @EpicPandaForce

Thank you all very much

Answer 1

this is what in PetDao.java

@Query("DELETE FROM pets")
int deleteAllPets();

In your PetRepository.java

private static class DeleteAllPetsAsyncTask extends AsyncTask<Void, Void, Integer>
    {
        private PetDao petDaoOfDeleteAllAsyncTask;
        public MutableLiveData<Integer> resultLiveData = new MutableLiveData();

        DeleteAllPetsAsyncTask(PetDao petDao)
        {
            this.petDaoOfDeleteAllAsyncTask = petDao;
        }

        @Override
        protected Integer doInBackground(Void... voids)
        {
            int countOfDeletedRows = this.petDaoOfDeleteAllAsyncTask.deleteAllPets();
            return countOfDeletedRows;
        }

        /**
         * <p>Runs on the UI thread after {@link #doInBackground}. The
         * specified result is the value returned by {@link #doInBackground}.</p>
         *
         * <p>This method won't be invoked if the task was cancelled.</p>
         *
         * @param integer The result of the operation computed by {@link #doInBackground}.
         * @see #onPreExecute
         * @see #doInBackground
         * @see #onCancelled(Object)
         */
        @Override
        protected void onPostExecute(Integer integer) {
            //super.onPostExecute(integer);
            // TODO: how to return this integer
            resultLiveData.postValue(integer);
        }
    }

    // this function is inside repository
    public LiveData<Integer> deleteAllPets()
    {
        DeleteAllPetsAsyncTask task = new DeleteAllPetsAsyncTask(this.petDao);
        task.execute();
        // I edited here
        return task.resultLiveData;
    }

In PetViewModel.java

public LiveData<Integer> deleteAllPets() {
    return this.petRepository.deleteAllPets();
}

In CatalogActivity.java

//
    private void deleteAllPets() {
        // TODO: Implement this method
        //
        Log.v(this.LOG_TAG, "rows deleted from pet database count is: ");

        this.petViewModel.deleteAllPets().observe(this,new Observer<Integer>(){
            @Override
            public void onChanged(final Integer result) {
                // here you will get result
                if (result == 0) {
                    // If no rows were deleted, then there was an error with the delete.
                    Toast.makeText(this, super.getString(R.string.catalog_delete_all_pets_failed) +
                    " ", Toast.LENGTH_LONG).show();
                } else {
                    // Otherwise, the delete was successful and we can display a toast.
                    Toast.makeText(this, super.getString(R.string.catalog_delete_all_pets_successful) +
                    " ", Toast.LENGTH_LONG).show();
                }
               // Close the activity
               //super.finish();
            }
        });
        // Show a toast message depending on whether or not the delete was successful.
    }