创建单个 weekOfYear NSDate 对象

Question

我正在用这个函数创建 NSDate 对象

-(NSDate *)createDate:(int)Year :(int)WeekOfYear{
    NSDateComponents *components = [[NSDateComponents alloc] init];
    [components setYear:Year];
    [components setWeekOfYear:WeekOfYear];
    NSDate *date = [_calendar dateFromComponents:components];
    return date;
}

当我循环插入 2015 年，然后是第 1 周到第 52 周。 它只用这个创建 52 个 NSDate 对象

2014-12-31 13:00:00 +0000

我怎样才能让它有效地创造一年中每个星期的开始？

Answer 1

这对你来说可能为时已晚，但也许对其他人有用。

因此，您不能这样做，因为 weekOfYear 是根据完全构造的 NSDateComponents 计算的，该组件是从完全构造的 NSDate 创建的。 你可以做的是这样的：

func getFirstDaysOfWeekInYear(year: Int) -> [NSDate] {
  var arrayOfFirstDayOfWeek : [NSDate] = []
  let calendar = NSCalendar.currentCalendar()
  let firstDayOfYearComponents = NSDateComponents()
  firstDayOfYearComponents.day = 1
  firstDayOfYearComponents.month = 1
  firstDayOfYearComponents.year = year
  let firstDayOfYearDate = calendar.dateFromComponents(firstDayOfYearComponents)!

  // if the first day of the year is not a monday, this will give you the first day of
  // the last week of the previous year, it's up to you if you want to remove it or not
  let firstWeekOfYearDate = self.roundWeekDayToFirstWeekDay(firstDayOfYearDate)

  arrayOfFirstDayOfWeek.append(firstWeekOfYearDate)
  for i in 1 ... 52 {
    let componentsToAdd = NSDateComponents()
    componentsToAdd.weekOfYear = i
    arrayOfFirstDayOfWeek.append(calendar.dateByAddingComponents(componentsToAdd, toDate: firstWeekOfYearDate, options: [])!)
  }
  return arrayOfFirstDayOfWeek
}

func roundWeekDayToFirstWeekDay(date: NSDate) -> NSDate {
  let calendar = NSCalendar.currentCalendar()
  let dateComponents : NSDateComponents = calendar
    .components([NSCalendarUnit.Year, NSCalendarUnit.Month, NSCalendarUnit.Day],
      fromDate: date)
  let keyDateComponents = NSDateComponents()
  let dayOfWeek = Int(date.stringFromDate(format: "e"))!
  let differenceToMonday = (dayOfWeek == 1 ? 6 : dayOfWeek - 2)
  keyDateComponents.day = dateComponents.day - differenceToMonday
  keyDateComponents.month = dateComponents.month
  keyDateComponents.year = dateComponents.year
  return calendar.dateFromComponents(keyDateComponents)!
}