import com.prolificinteractive.materialcalendarview.OnMonthChangedListener; //导入依赖的package包/类
@Override
@UiThread
public void call(final Subscriber<? super YearMonth> subscriber) {
  checkUiThread();

  calendarView.setOnMonthChangedListener(new OnMonthChangedListener() {
    @Override
    public void onMonthChanged(MaterialCalendarView widget, CalendarDay date) {
      if (!subscriber.isUnsubscribed()) {
        subscriber.onNext(DateHelper.calendarDayToYearMonth(date));
      }
    }
  });

  subscriber.add(new MainThreadSubscription() {
    @Override
    protected void onUnsubscribe() {
      calendarView.setOnMonthChangedListener(null);
    }
  });
}