swift - 在没有 WeekCalendarUnit 的情况下获取一周的第一天

Question

我想根据 NSDate 获取一周的第一天。

它工作正常，但我有一个警告，因为 WeekCalendarUnit 已被弃用。

我做了一些研究，并尝试将 WeekCalendarUnit 替换为:

static var CalendarUnitWeekday: NSCalendarUnit { get }
static var CalendarUnitWeekdayOrdinal: NSCalendarUnit { get }
static var CalendarUnitWeekOfMonth: NSCalendarUnit { get }
static var CalendarUnitWeekOfYear: NSCalendarUnit { get }

但我没有得到相同的结果。这是我的代码垃圾:

var date = NSDate()
dateFormatter.dateFormat = "dd/YY"
let calendar = NSCalendar.currentCalendar()
let currentDateComponents = calendar.components(.CalendarUnitYear | .WeekCalendarUnit , fromDate: date)
let startOfWeek = calendar.dateFromComponents(currentDateComponents)
var dteString = dateFormatter.stringFromDate(startOfWeek!)
// Output is "17/15" 

有什么想法吗？

Answer 1

您可以结合使用 .CalendarUnitWeekOfYear.CalendarUnitYearForWeekOfYear，这应该会给出预期的结果:

let currentDateComponents = calendar.components(.CalendarUnitYearForWeekOfYear | .CalendarUnitWeekOfYear , fromDate: date)
let startOfWeek = calendar.dateFromComponents(currentDateComponents)

或者，使用 rangeOfUnit()(我个人觉得更容易使用):

var startOfWeek : NSDate?
calendar.rangeOfUnit(.CalendarUnitWeekOfYear, startDate: &startOfWeek, interval: nil, forDate: date)

在 Swift 2 中，这必须更改为

let currentDateComponents = calendar.components([.YearForWeekOfYear, .WeekOfYear ], fromDate: date)
let startOfWeek = calendar.dateFromComponents(currentDateComponents)

和

var startOfWeek : NSDate?
calendar.rangeOfUnit(.WeekOfYear, startDate: &startOfWeek, interval: nil, forDate: date)