iOS开发 字符串转化为NSDate格式比较时间

求助 "2015/10/15 9:00:00" 这是一个网络解析下来的时间我想将她转化为NSDate格式,然后和当前时间进行比较,请问我应该怎么做?在线等

#define kShortTimeFormat @"yyyy-MM-dd"
//输入的日期字符串形如：@"1992-05-21 13:08:08"

• (NSDate *)dateFromString:(NSString *)dateString format:(NSString *)format
  {
  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

  [dateFormatter setDateFormat: format];
  dateFormatter.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"zh_CN"];

  NSDate *destDate= [dateFormatter dateFromString:dateString];

  return destDate;
  }
  //计算两个NSDate相差多少天

• (int)daysAwayFrom:(NSDate *)dateFirst dateSecond:(NSDate *)dateSecond {
  double timezoneFix = [NSTimeZone localTimeZone].secondsFromGMT;
  return (int)(([dateFirst timeIntervalSince1970] + timezoneFix)/(24*3600)) - (int)(([dateSecond timeIntervalSince1970] + timezoneFix)/(24*3600));
  }
  //比较两个NSString的时间(datefirst 比datesecond 早)

• (BOOL)daysAwayFromString:(NSString *)dateFirst dateSecondString:(NSString *)dateSecond
  {
  NSDate *firstDate = [self dateFromString:dateFirst format:kShortTimeFormat];
  NSDate *secondDate = [self dateFromString:dateSecond format:kShortTimeFormat];
  if([self daysAwayFrom:firstDate dateSecond:secondDate] < 0){
  return YES;
  }
  return NO;
  }

NSString *time = @"2015/10/15 9:00:00";
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd HH:mm"];
NSDate *date = [formatter dateFromString:time];