LoginActivity.java

public class LoginActivity extends AppCompatActivity {

    //... some fields here

    private BroadcastReceiver mLoginBroadcastReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);

        mLogin = (TextView) findViewById(R.id.login);
        mPassword = (TextView) findViewById(R.id.password);

        Button performLoginButton = (Button) findViewById(R.id.perform_login);
        performLoginButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                String login = mLogin.getText().toString();
                String password = mPassword.getText().toString();

                performLoginViaService(login, password);
            }
        });
    }

    private void performLoginViaService(String login, String password) {
        mLoginBroadcastReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                unregisterReceiver(this);
                mLoginBroadcastReceiver = null;

                LoginResponse loginResponse = LoginResponse.getLoginResponse(intent);
                handleLoginResponse(loginResponse);
            }
        };
        registerReceiver(mLoginBroadcastReceiver, new IntentFilter(LOGIN_RECEIVER_FILTER));
        LoginService.performAsyncLogin(this, LOGIN_RECEIVER_FILTER, login, password);
    }

    /**
     * This is a method that will be overridden in order to test response.
     */
    @VisibleForTesting
    public void handleLoginResponse(LoginResponse loginResponse) {
        // handle login response here
    }
    // some code here
}

This is a LoginActivity that perform simple login with a help of service.