-(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);
}