同一日期的NSDate和NSDateComponent值的差异

Question

我创建了一个简单的函数来获取一周的第一天和最后一天。查看NSLog输出，我发现同一日期的NSDate描述符和组件日期返回了不同的值，为什么？

这里的NSLog输出：

NSDATE: 2011-04-03 22:00:00 +0000, DAY COMPONENT: 4 
NSDATE: 2011-04-09 22:00:00 +0000, DAY COMPONENT: 10 

正如您所看到的，第一行的NSDATE为3，day分量为4，第二行的NSDATE为9和10。

代码如下：

NSDate *date = [NSDate date]; //Today is  April 5th 2011
NSCalendar *cal =[[NSCalendar alloc]initWithCalendarIdentifier:NSGregorianCalendar];

[cal setFirstWeekday:2]; //My week starts from Monday

//DEFINE BEGINNING OF THE WEEK
NSDate *beginningOfWeek = nil;
[cal rangeOfUnit:NSWeekCalendarUnit startDate:&beginningOfWeek interval:nil forDate:date];
NSDateComponents *beginComponents = [cal components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekCalendarUnit | NSWeekdayCalendarUnit) fromDate:beginningOfWeek];

//DEFINE END OF THE WEEK, WITH 6 days OFFSET FROM BEGINNING
NSDateComponents *offset = [[NSDateComponents alloc]init];
[offset setDay:6];
NSDate *endOfWeek = [cal dateByAddingComponents:offset toDate:beginningOfWeek options:0];
NSDateComponents *endComponents = [cal components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekCalendarUnit | NSWeekdayCalendarUnit) fromDate:endOfWeek];

NSLog(@"NSDATE: %@, DAY COMPONENT: %d",beginningOfWeek, [beginComponents day]);
NSLog(@"NSDATE: %@, DAY COMPONENT: %d",endOfWeek,       [endComponents day]);

Answer 1

您的日期打印时区为+0000 (协调世界时)，而您的NSCalendar实例(以及您的NSDateComponents)使用的是设备的默认时区(我猜是UTC+2)。