IOS 时间和时间戳之间转化示例

- (NSString *)timeWithTimeIntervalString:(NSString *)timeString
{
  // 格式化时间
  NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
  formatter.timeZone = [NSTimeZone timeZoneWithName:@"shanghai"];
  [formatter setDateStyle:NSDateFormatterMediumStyle];
  [formatter setTimeStyle:NSDateFormatterShortStyle];
  [formatter setDateFormat:@"yyyy年MM月dd日 HH:mm"];
  
  // 毫秒值转化为秒
  NSDate* date = [NSDate dateWithTimeIntervalSince1970:[timeString doubleValue]/ 1000.0];
  NSString* dateString = [formatter stringFromDate:date];
  return dateString;
}

    // 当前时间
   NSDate* date = [NSDate dateWithTimeIntervalSinceNow:0];
  NSTimeInterval a=[date timeIntervalSince1970]*1000; // *1000 是精确到毫秒，不乘就是精确到秒
  NSString *timeString = [NSString stringWithFormat:@"%.0f", a]; //转为字符型

- (void)getBabyDetailAge:(NSString *)date
{
  // 获得日期对象
  NSDateFormatter *formatter_ = [[NSDateFormatter alloc] init];
  formatter_.dateFormat = @"yyyy-MM-dd HH:mm:ss";
  NSDate *createDate = [formatter_ dateFromString:date];
  
  NSCalendar *gregorian = [[ NSCalendar alloc ] initWithCalendarIdentifier : NSCalendarIdentifierGregorian];
  NSUInteger unitFlags = NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear;
  NSDateComponents *components = [gregorian components:unitFlags fromDate:createDate toDate:[NSDate date] options: 0 ];
  
  NSInteger years = [components year];
  NSInteger months = [components month ];
  NSInteger days = [components day ];
}