我正在尝试NSDate使用以下代码获取一年中的第几周：
int which = NSYearCalendarUnit | NSMonthCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit | NSWeekOfYearCalendarUnit | NSQuarterCalendarUnit;
NSDate* date= [NSDate date];
NSDateComponents* comps= [[NSCalendar currentCalendar] components:which fromDate:date];
today.weekNumber= comps.weekOfYear;
但是，由于某种原因，它正在崩溃并声明：
reason: -[NSDateComponents weekOfYear]: unrecognized selector sent to instance
当我取消注释 weeknumber 部分时，其他组件工作得很好：
int which = NSYearCalendarUnit | NSMonthCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit | NSWeekOfYearCalendarUnit | NSQuarterCalendarUnit;
NSDate* date= [NSDate date];
NSDateComponents* comps= [[NSCalendar currentCalendar] components:which fromDate:date];
// today.weekNumber= comps.weekOfYear;
today.month= comps.month;
today.year= comps.year;
today.quarter= comps.quarter;
today.hour= comps.hour;
today.minute= comps.minute;
today.second= comps.second;
根据文档，NSDateComponents应该有一个名为 的属性weekOfYear，不是吗？
我很困惑，真的。