Unarchive Array with NSKeyedUnarchiver unarchivedObject(ofClass:from:)

Question

Since upgrading to Swift 4.2 I've found that many of the NSKeyedUnarchiver and NSKeyedArchiver methods have been deprecated and we must now use the type method static func unarchivedObject<DecodedObjectType>(ofClass: DecodedObjectType.Type, from: Data) -> DecodedObjectType? to unarchive data.

I have managed to successfully archive an Array of my bespoke class WidgetData, which is an NSObject subclass:

private static func archiveWidgetDataArray(widgetDataArray : [WidgetData]) -> NSData {

    guard let data = try? NSKeyedArchiver.archivedData(withRootObject: widgetDataArray as Array, requiringSecureCoding: false) as NSData
        else { fatalError("Can't encode data") }

    return data

}

The problem comes when I try to unarchive this data:

static func loadWidgetDataArray() -> [WidgetData]? {

    if isKeyPresentInUserDefaults(key: USER_DEFAULTS_KEY_WIDGET_DATA) {

        if let unarchivedObject = UserDefaults.standard.object(forKey: USER_DEFAULTS_KEY_WIDGET_DATA) as? Data {

            //THIS FUNCTION HAS NOW BEEN DEPRECATED:
            //return NSKeyedUnarchiver.unarchiveObject(with: unarchivedObject as Data) as? [WidgetData]

            guard let nsArray = try? NSKeyedUnarchiver.unarchivedObject(ofClass: NSArray.self, from: unarchivedObject as Data) else {
                fatalError("loadWidgetDataArray - Can't encode data")
            }

            guard let array = nsArray as? Array<WidgetData> else {
                fatalError("loadWidgetDataArray - Can't get Array")
            }

            return array

        }

    }

    return nil

}

But this fails, as using Array.self instead of NSArray.self is disallowed. What am I doing wrong and how can I fix this to unarchive my Array?

Answer 1

You can use unarchiveTopLevelObjectWithData(_:) to unarchive the data archived by archivedData(withRootObject:requiringSecureCoding:). (I believe this is not deprecated yet.)

But before showing some code, you should better:

• Avoid using NSData, use Data instead

• Avoid using try? which disposes error info useful for debugging

• Remove all unneeded casts

---

Try this:

private static func archiveWidgetDataArray(widgetDataArray : [WidgetData]) -> Data {
    do {
        let data = try NSKeyedArchiver.archivedData(withRootObject: widgetDataArray, requiringSecureCoding: false)

        return data
    } catch {
        fatalError("Can't encode data: \(error)")
    }

}

static func loadWidgetDataArray() -> [WidgetData]? {
    guard
        isKeyPresentInUserDefaults(key: USER_DEFAULTS_KEY_WIDGET_DATA), //<- Do you really need this line?
        let unarchivedObject = UserDefaults.standard.data(forKey: USER_DEFAULTS_KEY_WIDGET_DATA)
    else {
        return nil
    }
    do {
        guard let array = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(unarchivedObject) as? [WidgetData] else {
            fatalError("loadWidgetDataArray - Can't get Array")
        }
        return array
    } catch {
        fatalError("loadWidgetDataArray - Can't encode data: \(error)")
    }
}

---

But if you are making a new app, you should better consider using Codable.

Answer 2

unarchiveTopLevelObjectWithData(_:) 

is deprecated as well. So to unarchive data without secure coding you need to:

1. Create NSKeyedUnarchiver with init(forReadingFrom: Data)
2. Set requiresSecureCoding of created unarchiver to false.
3. Call decodeObject(of: [AnyClass]?, forKey: String) -> Any? to get your object, just use proper class and NSKeyedArchiveRootObjectKeyas key.

Answer 3

 if #available(iOS 12.0, *) {
        guard let unarchivedFavorites = try? NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(favoritesData!)
            else {
                return
        }
        self.channelFavorites = unarchivedFavorites as! [ChannelFavorite]
    } else {
        if let unarchivedFavorites = NSKeyedUnarchiver.unarchiveObject(with: favoritesData!) as? [ChannelFavorite] {
            self.channelFavorites = unarchivedFavorites
        }

// Achieving data

 if #available(iOS 12.0, *) {
            // use iOS 12-only feature
            do {
                let data = try NSKeyedArchiver.archivedData(withRootObject: channelFavorites, requiringSecureCoding: false)
                UserDefaults.standard.set(data, forKey: "channelFavorites")
            } catch {
                return
            }
        } else {
            // handle older versions
            let data = NSKeyedArchiver.archivedData(withRootObject: channelFavorites)
            UserDefaults.standard.set(data, forKey: "channelFavorites")
        }

This is the way I have updated my code and its working for me

Answer 4

You are likely looking for this:

if let widgetsData = UserDefaults.standard.data(forKey: USER_DEFAULTS_KEY_WIDGET_DATA) {
        if let widgets = (try? NSKeyedUnarchiver.unarchivedObject(ofClasses: [NSArray.self, WidgetData.self], from: widgetsData)) as? [WidgetData] {
            // your code
        }
    }