MainActivity.java

viewModel.login()
         .subscribeWith(new DisposableSingleObserver<Result>() {
                    @Override
                    public void onSuccess(Result result) {
                        //Handle Success
                    }

                    @Override
                    public void onError(Throwable e) {
                          if (e instanceof NetworkInterceptor.NoNetworkException) {
                            //Handle Network error
                          }
                    }
                }));