updateSecondIndex method
更新第二列索引
Implementation
@override
void updateSecondIndex(int index) {
super.updateSecondIndex(index);
int minSemiannual = getSemiannual(_minMonthOfCurrentYear());
int month = getMonthBySemiannual(minSemiannual + index);
currentTime = currentTime.isUtc
? DateTime.utc(currentTime.year, month)
: DateTime(currentTime.year, month);
}