斯威夫特 - 从一年中获取日期 [英] Swift - Get date from day of year

问题描述

我们可以使用以下行获取日期的日期。

We can get day of year for date using below line.

let day = cal.ordinalityOfUnit(.Day, inUnit: .Year, forDate: date)

但我们如何才能从一年中的某一天获得日期？ / p>

But how can we get the date from day of year?

推荐答案

如果您知道年份，您可以获得DateComponents日期属性，如下所示：

If you know the year you can get DateComponents date property as follow:

extension Calendar {
    static let iso8601 = Calendar(identifier: .iso8601)
}


let now = Date()
let day  = Calendar.iso8601.ordinality(of: .day, in: .year, for: now)!  // 121
let year = Calendar.iso8601.ordinality(of: .year, in: .era, for: now)!  // 2017
let date = DateComponents(calendar: .iso8601, year: year, day: day).date   //  "May 1, 2017, 12:00 AM"

或使用DateFormatter

or using DateFormatter

let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy D"
if let date = dateFormatter.date(from: "\(year) \(day)") {
    dateFormatter.dateStyle = .medium
    dateFormatter.timeStyle = .short
    dateFormatter.string(from: date)    // "May 1, 2017, 12:00 AM"
}

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