根据时间戳(或NSDate) 计算时间差

NSDateFormatter *date = [[NSDateFormatteralloc]init];

    [date setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

    NSDate *startD =[date dateFromString:startTime];

    NSDate *endD = [date dateFromString:endTime];

    NSTimeInterval start = [startD timeIntervalSince1970]*1;

    NSTimeInterval end = [endDtimeIntervalSince1970]*1;

    NSTimeInterval value = end - start;

    int second = (int)value %60;//秒

    int minute = (int)value /60%60;

    int house = (int)value / (24 *3600)%3600;

    int day = (int)value / (24 *3600);

    NSString *str;

    if (day != 0) {

        str = [NSString stringWithFormat:@"耗时%d天%d小时%d分%d秒",day,house,minute,second];

    }else if (day==0 && house !=0) {

        str = [NSString stringWithFormat:@"耗时%d小时%d分%d秒",house,minute,second];

    }else if (day==0 && house==0 && minute!=0) {

        str = [NSString stringWithFormat:@"耗时%d分%d秒",minute,second];

    }else{

        str = [NSString stringWithFormat:@"耗时%d秒",second];

    }