Having Issue with store non property object - ios

Question

I am trying to save store a custom file using UserDefaults, but my app crashesh due to :
fatal error: unexpectedly found nil while unwrapping an Optional value
Here is my code , in my custom class I declare an empty array
class AppDefualts: NSObject {
var downloadedURLArray = [DownloadFile]() //Declare an empty array
override init() {
super.init()
downloadedURLArray = loadStoredURL()
}
//Store data
func addStored(file:DownloadFile) {
//Add URL to array and save it
downloadedURLArray.append(file)
let data = NSKeyedArchiver.archivedData(withRootObject: downloadedURLArray)
UserDefaults.standard.set(data, forKey: "storedURL")
}
//Load:
func loadStoredURL() -> Array<DownloadFile> {
let data = UserDefaults.standard.data(forKey: "storedURL")
downloadedURLArray = NSKeyedUnarchiver.unarchiveObject(with: data!) as? [DownloadFile] ?? [DownloadFile]()
return downloadedURLArray
}
Any help would be great
EDIT 1 :
I added NSCoding protocols :
func encode(with aCoder: NSCoder) {
aCoder.encode(downloadedURLArray, forKey: "storedURL")
}
required init?(coder aDecoder: NSCoder) {
downloadedURLArray = aDecoder.decodeObject(forKey: "storedURL") as! [DownloadFile]
}
now app crashes due to this :
* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '* -encodeObject:forKey:
cannot be sent to an abstract object of class NSCoder: Create a
concrete instance!'

Answer 1

If you want to store the custom object in UserDefault then you have to do Encoding/Decoding. Your custom object suppose to confirm to the NSCoding Protocol.
Store into UserDefault : You have to convert you object in to NSData and store them into UserDefault by using NSKeyedArchiver
Get from UserDefault : Get the NSData from USerDefault and convert into Custom object by using NSKeyedUnArchiver
Refer the link to convert custom object into NSData and vice versa
Example: custom object which confirms NSCoding protocol
class Book: NSObject, NSCoding {
var title: String
var author: String
var pageCount: Int
var categories: [String]
var available: Bool
// Memberwise initializer
init(title: String, author: String, pageCount: Int, categories: [String], available: Bool) {
self.title = title
self.author = author
self.pageCount = pageCount
self.categories = categories
self.available = available
}
// MARK: NSCoding
required convenience init?(coder decoder: NSCoder) {
guard let title = decoder.decodeObjectForKey("title") as? String,
let author = decoder.decodeObjectForKey("author") as? String,
let categories = decoder.decodeObjectForKey("categories") as? [String]
else { return nil }
self.init(
title: title,
author: author,
pageCount: decoder.decodeIntegerForKey("pageCount"),
categories: categories,
available: decoder.decodeBoolForKey("available")
)
}
func encodeWithCoder(coder: NSCoder) {
coder.encodeObject(self.title, forKey: "title")
coder.encodeObject(self.author, forKey: "author")
coder.encodeInt(Int32(self.pageCount), forKey: "pageCount")
coder.encodeObject(self.categories, forKey: "categories")
coder.encodeBool(self.available, forKey: "available")
}
}