code: @Override
      public void onCheckedChanged(RadioGroup group, int checkedId) {
          if (checkedId == R.id.repeatMonthlyByNthDayOfMonth) {
              mModel.monthlyRepeat = RecurrenceModel.MONTHLY_BY_DATE;
          } else if (checkedId == R.id.repeatMonthlyByNthDayOfTheWeek) {
              mModel.monthlyRepeat = RecurrenceModel.MONTHLY_BY_NTH_DAY_OF_WEEK;
          }
          updateDialog();
      }
docs: Month repeat by radio buttons