我應該如何在目標C中找到過去的日期？

Question

如何獲得目標C中的過去日期？像，

NSDate *pastDate = //some date 2 weeks ago 

Answer 1

假設你不關心DST，

NSDate* pastDate = [NSDate dateWithTimeIntervalSinceNow:-2*7*24*60*60]; 

// Get the date which is exactly 2 weeks (14 days) ago. 

Answer 2

了我的頭頂部：

NSDate *today = [NSDate date]; 
NSDateComponents *dc = [[[NSDateComponents alloc] init] autorelease]; 
[dc setDay:-14]; 
NSCalendar *cal = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease]; 
NSDate *pastDate = [cal dateByAddingComponents:dc toDate:today options:0]; 

Answer 3

NSDate *today = [NSDate date]; 
NSLog(@"today: %@",today); 

NSDateComponents *dateComponents = [[NSDateComponents alloc] init]; 
[dateComponents setWeek:-2]; 
NSCalendar *currentCalendar = [NSCalendar currentCalendar]; 
NSDate *pastDate = [currentCalendar dateByAddingComponents:dateComponents toDate:today options:0]; 
NSLog(@"pastDate: %@",pastDate); 

的NSLog輸出：

today: 2011-12-07 11:52:15 +0000 
pastDate: 2011-11-23 11:52:15 +0000 

這個例子使用ARC。