将日期格式iso-8601更改为自定义格式

Question

I have a json file being parsed using JSONDecoder(). However, I receive the variable timestamp of type Date in iso-8601-format ("yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX") but on my view, I want to display it in a custom format: "dd/mm/yy HH:mm:ss".

I have written the following code, but I get nil for timestamp and furthermore I assume "date" is not the correct type to use when timestamp comes in iso-8601 format:

Error json: typeMismatch(Swift.Double, Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: "timestamp", intValue: nil)], debugDescription: "Expected to decode Double but found a string/data instead.", underlyingError: nil))

swift4

import UIKit

enum Type : String, Codable {
    case organizational, planning
}

// structure from json file
struct News: Codable{
    let type: Type
    let timestamp: Date //comes in json with ISO-8601-format
    let title: String
    let message: String

    enum  CodingKeys: String, CodingKey { case type, timestamp, title, message}

    let dateFormatter : DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateFormat = "dd/MM/yy HH:mm:ss"  // change format ISO-8601 to dd/MM/yy HH:mm:ss
        return formatter
    }()

    var dateString : String {
        return dateFormatter.string(from:timestamp) // take timestamp variable of type date and make it a string -> lable.text
    }
}

Answer 1

When you are decoding a Date the decoder expects an UNIX timestamp (a Double ) by default, this is what the error message tells you.

However you can indeed decode an ISO8601 string as Date if you add the decoder.dateDecodingStrategy = .iso8601 but this decodes only standard ISO8601 strings without milliseconds.

There are two options:

1. Add a formatted dateDecodingStrategy with a DateFormatter .

    let dateFormatter = DateFormatter() dateFormatter.locale = Locale(identifier: "en_US_POSIX") dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX" let decoder = JSONDecoder() decoder.dateDecodingStrategy = .formatted(dateFormatter) try decoder.decode(... 

2. Declare timestamp as

    let timestamp: String 

   and convert the string back and forth with two formatters or two date formats in dateString .