将UNIX时间从json导入（swift结构）转换为日期作为字符串并填充表

Question

I have a json file being imported to my project ( https://api.myjson.com/bins/ywv0k ). The json attributes are decoded and stored in my struct class "News", which has the same attributes like the json file.

in a second step I populate a table with the string attribute "timestamp" from my struct class "News", which is actually a UNIX time.

My problem now is that I am lost how to change this UNIX time to a string of format "dd/mm/yy HH:mm:ss", since I get an error when I try to put a function

let date = NSDate(timeIntervalSince1970: timestamp) //error since timestamp is currently defined as string. If I make it a long variable, I cannot populate the table with it any more, since the label requires a text with string format.

let dayTimePeriodFormatter = NSDateFormatter()
dayTimePeriodFormatter.dateFormat = "dd/mm/yy HH:mm:ss"

 let dateString = dayTimePeriodFormatter.stringFromDate(date)

into the do-encoding-loop as well as when I put it into this table function: func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell.

Swift 4

import UIKit

// structure from json file
struct News: Codable{
    let type: String
    let timestamp: String // UNIX format, eg. "1531294146340"
    let title: String
    let message: String
}

class HomeVC: BaseViewController, UITableViewDelegate, UITableViewDataSource {
    var myNewsItems: [News] = []
    @IBOutlet weak var myNewTableView: UITableView!   

    override func viewDidLoad() {
        super.viewDidLoad()

        let nibName = UINib(nibName: "CustomTableViewCell", bundle: nil)
        myNewTableView.register(nibName, forCellReuseIdentifier: "tableViewCell")


// JSON Decoding

        let url=URL(string:"https://api.myjson.com/bins/ywv0k")
        let session = URLSession.shared
        let task = session.dataTask(with: url!) { (data, response, error) in

            guard let data = data else { return }

            do {
                let myNewsS = try
                    JSONDecoder().decode([News].self, from: data)
                print(myNewsS)

                self.myNewsItems = myNewsS
                DispatchQueue.main.async {
                    self.myNewTableView.reloadData()
                }
            } catch let jsonErr {
            }

        }
        task.resume()
    }

    func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return myNewsItems.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "tableViewCell", for: indexPath) as!
CustomTableViewCell

// populate table with json content
        cell.commonInit(timestamp: myNewsItems[indexPath.row].timestamp, message: myNewsItems[indexPath.row].message)

        return cell
    }

    func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
            cell.backgroundColor = UIColor(white: 1, alpha: 0.5)
    }
}

Answer 1

First of all the date format is wrong. It has to be "dd/MM/yy HH:mm:ss"

The most efficient solution – if you are responsible for the JSON – send the value for timestamp as Double . Then it's sufficient to declare timestamp

let timestamp: Date // UNIX format, eg. 1531294146340

and add the date decoding strategy

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .millisecondsSince1970

Another solution is to put the date conversion code into the struct

struct News: Codable{
    let type: String
    let timestamp: String // UNIX format, eg. "1531294146340"
    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"
        return formatter
    }()

    var dateString : String {
        let timeInterval = TimeInterval(timestamp)!
        let date = Date(timeIntervalSince1970: timeInterval / 1000)
        return dateFormatter.string(from:date)
    }
}

The computed property dateString contains the date string.

---

Further you could declare type as enum

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

struct News: Codable{
    let type: Type
...

Answer 2

You should be able to convert the timestamp to date and then format it to specific format and convert back to String to display on UILabel. See if the following helps

func string(from timestamp: String) -> String {
    if let timeInterval = TimeInterval(timestamp) {
        let date = Date(timeIntervalSince1970: timeInterval)
        let formatter = DateFormatter()
        formatter.dateFormat = "dd/MM/yy HH:mm:ss"
        return formatter.string(from: date)
    }
    return "" //return empty if somehow the timestamp conversion to TimeInterval (Double) fails
} 

Answer 3

1) As a first suggestion, do NOT store date as string for a number or reasons.

(Apple says to use the very basic type... so use a 64bit for UnixTimestamp OR NSDate.. far more flexible, for example performing calcs, difference, localisations and so on... (and far better memory usage.. (Ints do not even use ARC...))

(and use optional for fields.... far more secure..)

2) so use an extension to save as Date (for example)

Let's start from a int unixTimestamp:

(I added a complete sample for a controller...)

//
//  ViewController.swift
//  sampleDate
//
//  Created by ing.conti on 16/08/2018.
//  Copyright © 2018 com.ingconti. All rights reserved.
//

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        //sample with int...

        if let dm =
            // Thursday, January 1, 2015 12:00:00 AM GMT+01:00
            (1420066800000/1000).fromUnixTimeStamp(){
            // note: usual timestamp from server come with milliseincods..

            //now You get a date... use and format!
            print(dm.description)
        }

        let testString = "1420066800"
        if let n = Int(testString), let dm = n.fromUnixTimeStamp(){
                print(dm.description)
            }
        }

}





extension Int {

    func  fromUnixTimeStamp() -> Date? {
        let date = Date(timeIntervalSince1970: TimeInterval(self))
        return date
}

}

so use extension AND change your to use date.

A final note: codable is fine, but not fine for "edge cases"ad apple says in "Reflecting on Reflection" ( https://developer.apple.com/swift/blog/?id=37 ) sometimes is better to write parser by hand... for a small piece of JSON.

So for example use:

(I rewrote a bit your class...)

typealias Dict = [String : Any]



struct News{
    let type: String?
    // NO! let timestamp: String // UNIX format, eg. "1531294146340"
    let timestamp: Date?
    let title: String?
    let message: String?


    init?(dict : Dict?) {

        guard let d = dict else{
            return nil
        }

        if let s = d["timestamp"] as? String, let n = Int(s) {
            timestamp = n.fromUnixTimeStamp()
        }else{
            timestamp = nil // or other "default" ..
        }

        // go on parsing... other fields..


        if let s = d["type"] as? String{
            type = s
        }else{
            type = nil // or other "default" ..
        }

        if let s = d["title"] as? String {
            title = s
        }
        else{
            title = nil // or other "default" ..
        }

        if let s = d["message"] as? String {
            message = s
        }else{
            message = nil // or other "default" ..
        }
    }

}

so use in this way:

...

let new = News(dict: dict)

I usually extract data form JSON in this way:

...

      guard let json = try? JSONSerialization.jsonObject(with: data, options: []) as? Dict
                else{
                    return
            }

            guard let dict = json else{
                return
            }


..
        let new = News(dict: dict)