swift - 使用 DateComponents 创建日期

Question

我想得到一周的第一天和最后一天。但我的结果与苹果的文档不符: https://developer.apple.com/documentation/foundation/nsdatecomponents/1410442-weekday

这是我的功能:

func startAndEndDateOfWeek(weekOfYearWithYear: (week: Int,year: Int)) -> (start: Date, end: Date) {
    var output = (start: Date.init(), end: Date.init())

    let calendar = Calendar(identifier: .gregorian)
    var firstDayComponents = DateComponents()
    firstDayComponents.weekOfYear = weekOfYearWithYear.week
    firstDayComponents.yearForWeekOfYear = weekOfYearWithYear.year
    firstDayComponents.weekday = 1

    let firstDay = calendar.date(from: firstDayComponents)

    var lastDayComponents = DateComponents()
    lastDayComponents.weekOfYear = weekOfYearWithYear.week
    lastDayComponents.yearForWeekOfYear = weekOfYearWithYear.year
    lastDayComponents.weekday = 2

    let lastDay = calendar.date(from: lastDayComponents)
    output = (start: firstDay!, end: lastDay!)
    return output
}

.weekday = 2 -> 导致星期日而不是 0。

我也想要一整天而不是 16:00。

Answer 1

一些观察:

1. 在公历中，weekday = 1 表示星期日； weekday = 2 表示星期一；等。您可以查看 calendar.maximumRange(of: .weekday) 以获得有效值的范围，您可以查看 calendar.weekdaySymbols 以了解这些 weekDay 值表示(例如“Sun”、“Mon”、“Tue”、“Wed”、“Thu”、“Fri”和“Sat”)。

2. 你说:

   I also want to have the entire day and not 16:00.

   Date 对象引用一个时间点。所以它不能代表“一整天”。但它可以表示午夜(在 GMT/UTC/Zulu 中，您所在时区的午夜可能是下午 4 点)。

   或者，您可以返回一个 DateInterval，它代表一个时间范围。

   func interval(ofWeek week: Int, in year: Int) -> DateInterval {
       let calendar = Calendar.current
   
       let date = DateComponents(calendar: calendar, weekOfYear: week, yearForWeekOfYear: year).date!
       return calendar.dateInterval(of: .weekOfYear, for: date)!
   }
   

   然后

   let formatter = DateIntervalFormatter()
   formatter.dateStyle = .short
   formatter.timeStyle = .short
   
   let year = Calendar.current.component(.year, from: Date())
   let dateInterval = interval(ofWeek: 2, in: year)
   print(formatter.string(from: dateInterval))
   

   在美国地区，间隔从 1 月 6 日开始:

   1/6/19, 12:00 AM – 1/13/19, 12:00 AM

   而在德语语言环境中，间隔从 7 日开始:

   07.01.19, 00:00 – 14.01.19, 00:00

3. 如果你想要一周的第一天和一周的最后一天开始，你可以这样做:

   func startAndEndDate(ofWeek week: Int, in year: Int) -> (Date, Date) {
       let date = DateComponents(calendar: calendar, weekOfYear: week, yearForWeekOfYear: year).date!
       let lastDate = calendar.date(byAdding: .day, value: 6, to: date)!
   
       return (date, lastDate)
   }
   

   然后

   let formatter = DateFormatter()
   formatter.dateStyle = .short
   
   let year = Calendar.current.component(.year, from: Date())
   let (start, end) = startAndEndDate(ofWeek: 2, in: year)
   print(formatter.string(from: start), "-", formatter.string(from: end))