How to get the day based on a time field (seconds since midnight 1970)?

问题

I'm grabbing data from an api, and one of the values I'm getting is for day of the week, the data returned from api looks like this:

"time": 1550376000

I created this function to get the date:

  func getDate(value: Int) -> String {
        let date = Calendar.current.date(byAdding: .day, value: value, to: Date())
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "E"

        return dateFormatter.string(from: date!)
    }

but was told there is a much safer way to get it instead of assuming we get consecutive days starting with today. Does anyone know how to build a date out of the time field (it is seconds since midnight 1970) and then use Calendar and DateComponent to figure out the day?

回答1:

Looks like you are receiving json data so you should structure your data and conform to Decodable protocol to convert your data to an object properly structured.

struct Object: Decodable {
    let time: Date
}

Don't forget to set the decoder dateDecodingStrategy property to secondsSince1970

do {
    let obj = try decoder.decode(Object.self, from: Data(json.utf8))
    let date = obj.time   // "Feb 17, 2019 at 1:00 AM"
    print(date.description(with: .current))// "Sunday, February 17, 2019 at 1:00:00 AM Brasilia Standard Time\n"
} catch {
    print(error)
}

Then you just need to get the weekday component (1...7 = Sun...Sat) and get the calendar shortWeekdaySymbols (localised), subtract 1 from the component value and use it as index to get correspondent symbol. Same approach I used in this post How to print name of the day of the week? to get the full week day name:

extension Date {
    var weekDay: Int {
        return Calendar.current.component(.weekday, from: self)
    }
    var weekdaySymbolShort: String {
        return Calendar.current.shortWeekdaySymbols[weekDay-1]
    }
}

print(date.weekdaySymbolShort)   // "Sun\n"

回答2:

You can use Calendar to get date component from the Date:

let date = Date(timeIntervalSince1970: time)// time is your value 1550376000
let timeComponents = Calendar.current.dateComponents([.weekday, .day, .month, .year], from: date)
print("\(timeComponents.weekday) \(timeComponents.day!) \(timeComponents.month!) \(timeComponents.year!)") // print "7 16 2 2019"
print("\(\(Calendar.current.shortWeekdaySymbols[timeComponents.weekday!-1]))") // print "Sat"

Hope this helps.

来源：https://stackoverflow.com/questions/54727924/how-to-get-the-day-based-on-a-time-field-seconds-since-midnight-1970

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ios

swift

nscalendar