Swift - Weekday by current location by currentCale

问题:

Today is Wednesday and I have this code

let calendar:NSCalendar = NSCalendar.currentCalendar()
let dateComps:NSDateComponents = calendar.components(.CalendarUnitWeekday , fromDate: NSDate())
let dayOfWeek:Int = dateComps.weekday

dayOfWeek is 4, but today is 3rd day of the week in Bulgaria. Is in USA today is 4th day of the week? And how to determine when the week starts in different countries and regions ? On my iPhone locale and calendar are set to Bulgarian calendar and locale and it knows that the week starts on Monday on my iMac also, but when I execute code it writes me 4...

回答1:

For the Gregorian calendar, the weekday property of NSDateComponents is always 1 for Sunday, 2 for Monday etc.

NSCalendar.currentCalendar().firstWeekday

gives the (index of the) first weekday in the current locale, that could be 1 in USA and 2 in Bulgaria. Therefore

var dayOfWeek = dateComps.weekday + 1 - calendar.firstWeekday
if dayOfWeek <= 0 {
    dayOfWeek += 7
}

is the day of the week according to your locale. As a one-liner:

let dayOfWeek = (dateComps.weekday + 7 - calendar.firstWeekday) % 7 + 1

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Update for Swift 3:

let calendar = Calendar.current
var dayOfWeek = calendar.component(.weekday, from: Date()) + 1 - calendar.firstWeekday
if dayOfWeek <= 0 {
    dayOfWeek += 7
}