Swift-从一年中的日期获取日期

如果您知道年份，则可以获取DateComponents date属性，如下所示：

extension Calendar {    static let iso8601 = Calendar(identifier: .iso8601)}let now = Date()let day  = Calendar.iso8601.ordinality(of: .day, in: .year, for: now)!  // 121let year = Calendar.iso8601.component(.year, from: now)  // 2017let date = DateComponents(calendar: .iso8601, year: year, day: day).date   //  "May 1, 2017, 12:00 AM"

或使用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"}