使用 DateComponents 创建日期

问题描述

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匹配:

我也想要一整天而不是 16:00.

解决方案

几点观察:

1. 在公历中，weekday = 1 表示周日；weekday = 2 表示星期一；等你可以查看 calendar.maximumRange(of: .weekday) 来获取有效值的范围，你可以查看 calendar.weekdaySymbols 看看这些 weekDay 值表示(例如Sun"、Mon"、Tue"、Wed"、Thu"、Fri"和Sat").

2. 你说:

   我也想要一整天而不是 16:00.

   Date 对象引用了某个时刻.所以它不能代表一整天".但它可以代表午夜(您所在时区的午夜可能是 GMT/UTC/Zulu 下午 4 点).

   您也可以返回一个 DateInterval，它确实代表一个时间范围.

   func interval(ofWeek week: Int, in year: Int) ->日期间隔 {让日历 = Calendar.current让 date = DateComponents(calendar: calendar, weekOfYear: week, yearForWeekOfYear: year).date！返回 calendar.dateInterval(of: .weekOfYear, for: date)！}

   然后

   让 formatter = DateIntervalFormatter()格式化程序.dateStyle = .short格式化程序.timeStyle = .short让 year = Calendar.current.component(.year, from: Date())让 dateInterval = interval(ofWeek: 2, in: year)打印(formatter.string(来自:dateInterval))

   在美国地区，时间间隔从 1 月 6 日开始:

   19 年 1 月 6 日上午 12:00 – 19 年 1 月 13 日上午 12:00

   而在德国语言环境中，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的开始，你可以这样做:

   func startAndEndDate(ofWeek week: Int, in year: Int) ->(日期，日期){让 date = DateComponents(calendar: calendar, weekOfYear: week, yearForWeekOfYear: year).date！让 lastDate = calendar.date(byAdding: .day, value: 6, to: date)！返回(日期，最后日期)}

   然后

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

I want to get the first day and the last day of the week. But my results do not match the documentation from apple:https://developer.apple.com/documentation/foundation/nsdatecomponents/1410442-weekday

This is my function:

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 -> leads to the sunday and not 0.

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

解决方案

A couple of observations:

1. In the Gregorian calendar, weekday = 1 means Sunday; weekday = 2 means Monday; etc. You can look at calendar.maximumRange(of: .weekday) to get the range of valid values, and you can look at calendar.weekdaySymbols to see what these weekDay values mean (e.g. "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", and "Sat").

2. You said:

   A Date object references a moment in time. So it can’t represent an "entire day". But it can represent midnight (and midnight in your time zone is likely 4pm in GMT/UTC/Zulu).

   You can, alternatively, return a DateInterval, which does represent a range of time.

   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)!
   }
   

   And then

   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))
   

   In a US locale, the interval starts on January 6th:

   Whereas in a German locale, the interval starts on the 7th:

3. If you want the start of the first day of the week and the last day of the week, you can do:

   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)
   }
   

   And then

   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))
   

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