iOS日期加减计算

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

[dateFormatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"UTC"]];//格林尼治，世界标准时间
[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm"];

日期加

        NSDate *Date_sub = [NSDate  date];//格林尼治时间
        NSTimeInterval interval = 60 * 60 * 2; //秒数

        NSString *titleString = [dateFormatter stringFromDate:[Date_sub  initWithTimeInterval:interval  sinceDate:  Date_sub]];

日期减

         NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

         unsigned int unitFlags = NSHourCalendarUnit;//年、月、日、时、分、秒、周等等都可以
         NSDateComponents *comps = [gregorian components:unitFlags fromDate:Date1 toDate:Date2 options:0];

         int hours = [comps hour];//时间差