class AuthenticatorTask extends AsyncTask<Void, Void, Integer> {
        String username;
        String password;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            EditText usernameText = (EditText) findViewById(R.id.edit_text_username);
            EditText passwordText = (EditText) findViewById(R.id.edit_text_password);
            username = usernameText.getText().toString();
            password = passwordText.getText().toString();
        }


        @Override
        protected Integer doInBackground(Void... voids) {
            return new Authenticator().getUserId(username, password);
        }

        @Override
        protected void onPostExecute(Integer userId) {
            if (userId == -1) {
                Toast.makeText(SignInActivity.this, "Invalid username or password", Toast.LENGTH_SHORT).show();
            } else {
                startActivity(new Intent(SignInActivity.this, DashboardActivity.class));
                finish();
            }
        }
    }