获取3个月前的时间(获取某一天的时间 NSDate) --NSCalendar--NSDateComponents

-(void)getThreeMonthDate:(NSDate *)mydate

{

NSLog(@"%@",mydate);

//1.创建NSCalendar

NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];

//2.改变NSDateComponents

NSDateComponents *adcomps = [[NSDateComponents alloc] init];

[adcomps setYear:0];

[adcomps setMonth:-3];

[adcomps setDay:0];

//3.获取NSDate

NSDate *newdate = [calendar dateByAddingComponents:adcomps toDate:mydate options:0];

NSLog(@"%@",newdate);

}