计算时间差

gistfile1.m

#import "NSDate+Formatting.h"

#define SECONDS_PER_MINUTE 60.0
#define SECONDS_PER_HOUR   3600.0
#define SECONDS_PER_DAY    86400.0
#define SECONDS_PER_MONTH  2592000.0
#define SECONDS_PER_YEAR   31536000.0

@implementation NSDate (formatting)

- (NSString *)formatWithString:(NSString *)format {
  NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
  [formatter setDateFormat:format];
  NSString *string = [formatter stringFromDate:self];
  [formatter release];
  return string;
}

- (NSString *)formatWithStyle:(NSDateFormatterStyle)style {
  NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
  [formatter setDateStyle:style];
  NSString *string = [formatter stringFromDate:self];
  [formatter release];
  return string;
}

- (NSString *)distanceOfTimeInWords {
  return [self distanceOfTimeInWords:[NSDate date]];
}

- (NSString *)distanceOfTimeInWords:(NSDate *)date {
  NSString *Ago      = NSLocalizedString(@"ago", @"Denotes past dates");
  NSString *FromNow  = NSLocalizedString(@"from now", @"Denotes future dates");
  NSString *LessThan = NSLocalizedString(@"Less than", @"Indicates a less-than number");
  NSString *About    = NSLocalizedString(@"About", @"Indicates an approximate number");
  NSString *Over     = NSLocalizedString(@"Over", @"Indicates an exceeding number");
  NSString *Almost   = NSLocalizedString(@"Almost", @"Indicates an approaching number");
  //NSString *Second   = NSLocalizedString(@"second", @"One second in time");
  NSString *Seconds  = NSLocalizedString(@"seconds", @"More than one second in time");
  NSString *Minute   = NSLocalizedString(@"minute", @"One minute in time");
  NSString *Minutes  = NSLocalizedString(@"minutes", @"More than one minute in time");
  NSString *Hour     = NSLocalizedString(@"hour", @"One hour in time");
  NSString *Hours    = NSLocalizedString(@"hours", @"More than one hour in time");
  NSString *Day      = NSLocalizedString(@"day", @"One day in time");
  NSString *Days     = NSLocalizedString(@"days", @"More than one day in time");
  NSString *Month    = NSLocalizedString(@"month", @"One month in time");
  NSString *Months   = NSLocalizedString(@"months", @"More than one month in time");
  NSString *Year     = NSLocalizedString(@"year", @"One year in time");
  NSString *Years    = NSLocalizedString(@"years", @"More than one year in time");
  
  NSTimeInterval since = [self timeIntervalSinceDate:date];
  NSString *direction = since <= 0.0 ? Ago : FromNow;
  since = fabs(since);
  
  int seconds   = (int)since;
  int minutes   = (int)round(since / SECONDS_PER_MINUTE);
  int hours     = (int)round(since / SECONDS_PER_HOUR);
  int days      = (int)round(since / SECONDS_PER_DAY);
  int months    = (int)round(since / SECONDS_PER_MONTH);
  int years     = (int)floor(since / SECONDS_PER_YEAR);
  int offset    = (int)round(floor((float)years / 4.0) * 1440.0);
  int remainder = (minutes - offset) % 525600;
  
  int number;
  NSString *measure;
  NSString *modifier = @"";
  
  switch (minutes) {
    case 0 ... 1:
      measure = Seconds;
      switch (seconds) {
        case 0 ... 4:
          number = 5;
          modifier = LessThan;
          break;
        case 5 ... 9:
          number = 10;
          modifier = LessThan;
          break;
        case 10 ... 19:
          number = 20;
          modifier = LessThan;
          break;
        case 20 ... 39:
          number = 30;
          modifier = About;
          break;
        case 40 ... 59:
          number = 1;
          measure = Minute;
          modifier = LessThan;
          break;
        default:
          number = 1;
          measure = Minute;
          modifier = About;
          break;
      }
      break;
    case 2 ... 44:
      number = minutes;
      measure = Minutes;
      break;
    case 45 ... 89:
      number = 1;
      measure = Hour;
      modifier = About;
      break;
    case 90 ... 1439:
      number = hours;
      measure = Hours;
      modifier = About;
      break;
    case 1440 ... 2529:
      number = 1;
      measure = Day;
      break;
    case 2530 ... 43199:
      number = days;
      measure = Days;
      break;
    case 43200 ... 86399:
      number = 1;
      measure = Month;
      modifier = About;
      break;
    case 86400 ... 525599:
      number = months;
      measure = Months;
      break;
    default:
      number = years;
      measure = number == 1 ? Year : Years;
      if (remainder < 131400) {
        modifier = About;
      } else if (remainder < 394200) {
        modifier = Over;
      } else {
        ++number;
        measure = Years;
        modifier = Almost;
      }
      break;
  }
  if ([modifier length] > 0) {
    modifier = [modifier stringByAppendingString:@" "];
  }
  return [NSString stringWithFormat:@"%@%d %@ %@", modifier, number, measure, direction];
}

@end