iOS - 倒计时封装

+(NSString *)countdownStartTime:(NSString *)startTime{

    NSString *TIME = [startTime substringToIndex:];
    NSTimeInterval time = [TIME floatValue];
    NSDate *oldDate = [NSDate dateWithTimeIntervalSince1970:time];

    //    NSDate *oldDate = [NSDate date];
    NSDate *currentDate = [NSDate date];
    NSLog(@"lastDate == %@",currentDate);

    NSCalendar *cal = [NSCalendar currentCalendar];
    unsigned int unitFlags = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
    NSDateComponents *dateComponents = [cal components:unitFlags fromDate:oldDate toDate:currentDate options:];

    float sec = [dateComponents hour]* + [dateComponents minute]*+ [dateComponents second];

    float surplusMin = (* - sec)/;

    if (surplusMin == ) {
        return @"订单关闭";
    }else{
         return [NSString stringWithFormat:@"剩余：%d分%d秒", [dateComponents minute],[dateComponents second]];
    }
}