iOS - 倒计时封装

+(NSString *)countdownStartTime:(NSString *)startTime{
    
    
    NSString *TIME = [startTime substringToIndex:10];
    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:0];
    
    float sec = [dateComponents hour]*3600 + [dateComponents minute]*60+ [dateComponents second];
    
    float surplusMin = (30*60 - sec)/60;
    
    if (surplusMin == 00) {
        return @"订单关闭";
    }else{
         return [NSString stringWithFormat:@"剩余：%d分%d秒", [dateComponents minute],[dateComponents second]];
    }
}