// This method implements deleteAllBooks method of retrofit Interface. public void deleteAllBooks() { progressBar.setVisibility(ProgressBar.VISIBLE); RestAdapter adapter = new RestAdapter.Builder().setEndpoint(ENDPOINT).build(); retrofitInterface retro = adapter.create(retrofitInterface.class); retro.deleteAllBooks( new Callback<Book>() { @Override public void success(Book book, Response response) { bookList.clear(); updateDisplay(); Toast.makeText(getActivity(), R.string.delete_success, Toast.LENGTH_LONG).show(); progressBar.setVisibility(ProgressBar.GONE); } @Override public void failure(RetrofitError retrofitError) { progressBar.setVisibility(ProgressBar.GONE); Toast.makeText(getActivity(), R.string.delete_failed, Toast.LENGTH_LONG).show(); } }); }