如何从 NSDate 中找到一周的开始？

Question

我正在实现一个日历视图，我希望它在包含特定日期的一周开始时开始。例如。如果目标日期是 2016 年 2 月 29 日星期一，并且当前日历设置为从星期日开始，我希望我的视图从 2 月 28 日星期日开始。

这看起来应该很简单：

let calendar = NSCalendar.currentCalendar()
let firstDate = calendar.nextDateAfterDate(targetDate, 
                    matchingUnit: .Weekday,
                           value: calendar.firstWeekday,
                         options: .SearchBackwards)

但这失败了：

由于未捕获的异常“NSInvalidArgumentException”而终止应用，原因：“必须指定集合 {NSCalendarMatchPreviousTimePreservingSmallerUnits, NSCalendarMatchNextTimePreservingSmallerUnits, NSCalendarMatchNextTime} 中的一个选项。”

我基本上可以得到我想要的：

let firstDate = calendar.nextDateAfterDate(firstDate, 
                    matchingUnit: .Weekday,
                           value: calendar.firstWeekday,
                        options: .MatchPreviousTimePreservingSmallerUnits)?
                    .dateByAddingTimeInterval(-7 * 84600)

但这似乎是一种不好的做法，因为有时一天中的秒数不是 86400。

有没有更好的办法？

Answer 1

您可以使用Calendar 方法date(from: DateComponents) 从任何日期传递[.yearForWeekOfYear, .weekOfYear] 组件，它将从使用的日历返回一周的第一天。因此，如果您想获得星期天，只需使用公历。如果您想将星期一作为一周的第一天，您可以使用日历 .iso8601，正如您在 answer 中看到的那样

Xcode 12 • Swift 5.3 或更高版本（也适用于以前的 Swift 版本）

extension Calendar {
    static let gregorian = Calendar(identifier: .gregorian)
}

---

extension Date {
    func startOfWeek(using calendar: Calendar = .gregorian) -> Date {
        calendar.dateComponents([.calendar, .yearForWeekOfYear, .weekOfYear], from: self).date!
    }
}

---

用法：

Date().startOfWeek()  // "Sep 20, 2020 at 12:00 AM"

---

---

如果您想在特定时区获得一周的开始，您只需要使用自定义日历：

var gregorianUTC = Calendar.gregorian
gregorianUTC.timeZone = TimeZone(identifier: "UTC")!
print(Date().startOfWeek(using: gregorianUTC))  // "2020-09-20 00:00:00 +0000\n"

Answer 2

Swift 4 解决方案

我已经根据我的要求想通了，我在哪里找到了关注的日期。

1. Today

2. Tomorrow 

3. This Week 

4. This Weekend 

5. Next Week 

6. Next Weekend

所以，我创建了Date Extension 来获取当前周和下周的日期。

代码

extension Date {

    func getWeekDates() -> (thisWeek:[Date],nextWeek:[Date]) {
        var tuple: (thisWeek:[Date],nextWeek:[Date])
        var arrThisWeek: [Date] = []
        for i in 0..<7 {
            arrThisWeek.append(Calendar.current.date(byAdding: .day, value: i, to: startOfWeek)!)
        }
        var arrNextWeek: [Date] = []
        for i in 1...7 {
            arrNextWeek.append(Calendar.current.date(byAdding: .day, value: i, to: arrThisWeek.last!)!)
        }
        tuple = (thisWeek: arrThisWeek,nextWeek: arrNextWeek)
        return tuple
    }

    var tomorrow: Date {
        return Calendar.current.date(byAdding: .day, value: 1, to: noon)!
    }
    var noon: Date {
        return Calendar.current.date(bySettingHour: 12, minute: 0, second: 0, of: self)!
    }

    var startOfWeek: Date {
        let gregorian = Calendar(identifier: .gregorian)
        let sunday = gregorian.date(from: gregorian.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self))
        return gregorian.date(byAdding: .day, value: 1, to: sunday!)!
    }

    func toDate(format: String) -> String {
        let formatter = DateFormatter()
        formatter.dateFormat = format
        return formatter.string(from: self)
    }
}

用法：

let arrWeekDates = Date().getWeekDates() // Get dates of Current and Next week.
let dateFormat = "MMM dd" // Date format
let thisMon = arrWeekDates.thisWeek.first!.toDate(format: dateFormat)
let thisSat = arrWeekDates.thisWeek[arrWeekDates.thisWeek.count - 2].toDate(format: dateFormat)
let thisSun = arrWeekDates.thisWeek[arrWeekDates.thisWeek.count - 1].toDate(format: dateFormat)

let nextMon = arrWeekDates.nextWeek.first!.toDate(format: dateFormat)
let nextSat = arrWeekDates.nextWeek[arrWeekDates.nextWeek.count - 2].toDate(format: dateFormat)
let nextSun = arrWeekDates.nextWeek[arrWeekDates.nextWeek.count - 1].toDate(format: dateFormat)

print("Today: \(Date().toDate(format: dateFormat))") // Sep 26
print("Tomorrow: \(Date().tomorrow.toDate(format: dateFormat))") // Sep 27
print("This Week: \(thisMon) - \(thisSun)") // Sep 24 - Sep 30
print("This Weekend: \(thisSat) - \(thisSun)") // Sep 29 - Sep 30
print("Next Week: \(nextMon) - \(nextSun)") // Oct 01 - Oct 07
print("Next Weekend: \(nextSat) - \(nextSun)") // Oct 06 - Oct 07

您可以根据需要修改Extension。

谢谢！

Answer 3

您可以将其实现为 Date 类扩展或其他东西。它应该返回类似2020-01-06 00:00:00 +0000

Xcode 11.3 Swift 5

func firstDayOfWeek() -> Date {
    var c = Calendar(identifier: .iso8601)
    c.timeZone = TimeZone(secondsFromGMT: 0)!
    print(
        c.date(from: c.dateComponents([.weekOfYear, .yearForWeekOfYear], from: Date()))!
    )
} 

Answer 4

日历有一种机制可以在包含给定日期的给定时间间隔（例如一年中的一周或一个月）的开始处查找日期：

let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let date = dateFormatter.date(from: "2017-01-07")

if let date = date {
    let calendar = Calendar(identifier: .gregorian)

    var startDate : Date = Date()
    var interval : TimeInterval = 0

    if calendar.dateInterval(of: .weekOfYear, start: &startDate, interval: &interval, for: date) {
        print("Start of week is \(startDate)")
        // prints "Start of week is 2017-01-01 06:00:00 +0000"
    }
}

Answer 5

基本使用

NSCalender

和

dateByAddingComponents

。为了解决您的问题，请尝试使用此代码示例：

let cal = NSCalendar.currentCalendar()

let components = NSDateComponents()
components.weekOfYear -= 1

if let date = cal.dateByAddingComponents(components, toDate: NSDate(), options: NSCalendarOptions(0)) {
    var beginningOfWeek: NSDate?
    var weekDuration = NSTimeInterval()
    if cal.rangeOfUnit(.CalendarUnitWeekOfYear, startDate: &beginningOfWeek, interval: &weekDuration, forDate: date) {
         print(beginningOfWeek) 
    }
}

Answer 6

我之前的所有解决方案都有问题，因为它们没有考虑用户的日历设置。下一个代码将考虑到这一点。

extension Date {    

    var startOfWeek: Date? {
        let calendar = Calendar.current
        var components: DateComponents? = calendar.dateComponents([.weekday, .year, .month, .day], from: self)
        var modifiedComponent = components
        modifiedComponent?.day = (components?.day ?? 0) - ((components?.weekday ?? 0) - 1)

        return calendar.date(from: modifiedComponent!)
    }

    var endOfWeek: Date? {
        let calendar = Calendar.current
        var components: DateComponents? = calendar.dateComponents([.weekday, .year, .month, .day], from: self)
        var modifiedComponent = components
        modifiedComponent?.day = (components?.day ?? 0) + (7 - (components?.weekday ?? 0))
        modifiedComponent?.hour = 23
        modifiedComponent?.minute = 59
        modifiedComponent?.second = 59

        return calendar.date(from: modifiedComponent!)

    }
}

Answer 7

为了正确遵守用户的区域设置，您应该在DateComponents 中使用用户的Calendar firstWeekday 属性。这是我通常使用的：

// MARK: first day of week
extension Date {
  /**
    Finds the first day of the week the subject date falls into.
   
   - Parameter calendar: The calendar to use. Defaults to the user's current calendar.
   
   - Returns: The `Date` of the first day of the week into which the subject date falls.
   
   `startOfWeek()` respects the user's locale settings, i.e. will automatically use Sunday/Monday/etc. as first
   weekday based on the user's region and locale settings.
   */
  func startOfWeek(using calendar: Calendar = .current) -> Date? {
    var components = calendar.dateComponents([.weekday, .year, .month, .weekOfYear], from: self)
    components.weekday = calendar.firstWeekday
    return calendar.date(from: components)
  }
}