NSDate-常用操作及控制
对于NSDate常用操作整理，如有不足请补充

1，获取当前时区时间

NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];     NSInteger unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit |   NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;          NSDateComponents *comps  = [calendar components:unitFlags fromDate:date];          int year = [comps year];   int month = [comps month];   int day = [comps day];   int hour = [comps hour];   int min = [comps minute];   int sec = [comps second];