计算当前时间和指定时间的时间差

 *  计算剩余时间
 *
 *  @param endTime   结束日期
 *
 *  @return 剩余时间
 */
-(NSString *)getCountDownStringWithEndTime:(NSString *)endTime {
    
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm"];
    
    NSDate *now = [NSDate date];
    NSTimeZone *zone = [NSTimeZone systemTimeZone];//设置时区
    NSInteger interval = [zone secondsFromGMTForDate: now];
    NSDate *localDate = [now  dateByAddingTimeInterval: interval];
    endTime = [NSString stringWithFormat:@"%@ 23:59", endTime];
    NSDate *endDate = [dateFormatter dateFromString:endTime];
    NSInteger endInterval = [zone secondsFromGMTForDate: endDate];
    NSDate *end = [endDate dateByAddingTimeInterval: endInterval];
    NSUInteger voteCountTime = ([end timeIntervalSinceDate:localDate]) / 3600 / 24;

     NSString *timeStr = [NSString stringWithFormat:@"%d", voteCountTime];
    
    return timeStr;
}