ChronoActivity2.java

public class ChronoActivity2 extends AppCompatActivity {

    @Overrideprotected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // The ViewModelStore provides a new ViewModel or one previously created.

        ChronometerViewModel chronometerViewModel
                = ViewModelProviders.of(this).get(ChronometerViewModel.class);

        // Get the chronometer referenceChronometer chronometer = findViewById(R.id.chronometer);

        if (chronometerViewModel.getStartTime() == null) {
            // If the start date is not defined, it's a new ViewModel so set it.
            long startTime = SystemClock.elapsedRealtime();
            chronometerViewModel.setStartTime(startTime);
            chronometer.setBase(startTime);
        } else {
            // Otherwise the ViewModel has been retained, set the chronometer's base to the original// starting time.
            chronometer.setBase(chronometerViewModel.getStartTime());
        }

        chronometer.start();
    }
}