iOS日期的加减

NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    
    NSDateComponents *comps = nil;
    NSDate*nowDate = [NSDate  dateWithString:self.timeStamp formatterString:@"yyyy-MM"];
    comps = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit fromDate:nowDate];
    
    NSDateComponents *adcomps = [[NSDateComponents alloc] init];
    
    [adcomps setMonth:-1];
    NSDate *newdate = [calendar dateByAddingComponents:adcomps toDate:nowDate options:0];