ios - iOS 上的冬至日期

Question

我正在组装一个应用程序，该应用程序在夏至和冬至时都利用了太阳的位置。虽然那里有大量数据表，但我想知道是否有任何标准 iOS 组件可用于计算或检索冬至日期，而无需嵌入然后查找数据。

Answer 1

从评论中吸取建议，以下是我为从儒略日期中获取带有小时和分钟的公历日期而实现的方法。

- (NSDate *) dateFromJulianDate:(double)julianDate
{
  NSCalendar *gregorianCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
  NSDate *gregorianDate;

  double datePart = floor(julianDate);
  double timePart = julianDate - datePart + 0.5;

  // Really the next calendar day?
  if (timePart >= 1.0) {
    timePart = timePart - 1.0;
    datePart = datePart + 1;
  }

  double l = datePart + 68569;
  double n = floor (4 * l / 146097);
  l = floor(l) - floor((146097 * n + 3) / 4);
  int year = floor(4000 * (l + 1) / 1461001);
  l = l - (floor(1461 * year / 4)) + 31;
  int month = floor(80 * l / 2447);
  int day = l - floor(2447 * month / 80);
  l = floor(month / 11);
  month = floor(month + 2 - 12 * l);
  year = floor(100 * (n - 49) + year + l);
  double hour = timePart * 24.0;
  double minutePart = hour - floor(hour);
  hour = floor(hour);
  double minute = minutePart * 60;
  NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
  [dateComponents setYear:year];
  [dateComponents setMonth:month];
  [dateComponents setDay:day];
  [dateComponents setHour:hour];
  [dateComponents setMinute:minute];
  [dateComponents setTimeZone:[NSTimeZone timeZoneWithName:@"GMT"]];
  gregorianDate = [gregorianCalendar dateFromComponents:dateComponents];

  return [gregorianDate copy];
}