Creating a date with DateComponents

问题

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.

回答1:

A couple of observations:

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”).

You said:

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

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:

1/6/19, 12:00 AM – 1/13/19, 12:00 AM

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

07.01.19, 00:00 – 14.01.19, 00:00

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))

来源：https://stackoverflow.com/questions/54938512/creating-a-date-with-datecomponents

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swift

calendar

nsdatecomponents