Solution: The problem here was that I was using android.app.DialogFragment instead of android.support.v4 .app.Dialog.Fragment. So, I imported android.support.v4 library to my three classes (MainActivity, DatePickerFragment and TimePickerFragment.
Next step was changing the extends of my MainActivity class from Activity to FragmentActivity (changing the imports statements):
public class MainActivity extends FragmentActivity implements
DatePickerDialog.OnDateSetListener, TimePickerDialog.OnTimeSetListener {}
Finally, I changed getFragmentManager() for getSupportFragmentManager() in both classes:
public void showDatePickerDialog(View v) {
DatePickerFragment newFragment = new DatePickerFragment();
newFragment.show(getSupportFragmentManager(), "datePicker");
}
public void showTimePickerDialog(View v) {
DialogFragment newFragment = new TimePickerFragment();
newFragment.show(getSupportFragmentManager(), "timePicker");
}
Last step was testing on the android 2.3.3 emulator and it worked correctly.