使用dateByAddingTimeInterval方法:

use dateByAddingTimeInterval method:

NSDate *now = [NSDate date];
NSDate *sevenDaysAgo = [now dateByAddingTimeInterval:-7*24*60*60];
NSLog(@"7 days ago: %@", sevenDaysAgo);

输出:

7 days ago: 2012-04-11 11:35:38 +0000

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