"Value for key 'root' was unexpected class 'NSArray'" error when retrieve an array of object in UserDefault, Swift

Question

I'm trying to retrieve an array of custom object in Swift, where i get the error

"UserInfo={NSDebugDescription=value for key 'root' was of unexpected class 'NSArray'. Allowed classes are '{(MusicCloud.Playlist)}"

My project is a music player, so I'm having a Song object and a Playlist object, which will have a name and list song songs.

I've already encode the object model:

class Playlist: NSObject, NSCoding{
    var name: String
    var songs: [Song]
    var image: UIImage

    override init() {
        self.name = ""
        self.songs = []
        self.image = UIImage()
    }

    init(name: String, songs: [Song], image: UIImage) {
        self.name = name
        self.songs = songs
        self.image = image
    }

    required convenience init(coder aDecoder: NSCoder) {
        let name = aDecoder.decodeObject(forKey: "name") as! String
        let songs = aDecoder.decodeObject(forKey: "songs") as! [Song]
        let image = aDecoder.decodeObject(forKey: "photo") as! UIImage
        self.init(name: name, songs: songs, image: image)
    }

    func encode(with aCoder: NSCoder) {
        aCoder.encode(name, forKey: "name")
        aCoder.encode(songs, forKey: "songs")
        aCoder.encode(image, forKey: "photo")
    }
}

Storing the playlists:

let playlist: Playlist = Playlist(name: txt.text!, songs: [], image: UIImage())
            MusicService.shared.playlists.append(playlist)
            do{
                let encodedData: Data = try NSKeyedArchiver.archivedData(withRootObject: MusicService.shared.playlists, requiringSecureCoding: false)
                self.userDefaults.set(encodedData, forKey: "playlist")
                self.userDefaults.synchronize()
            }catch let error{
                print("error when add  \(error)")
            }

And retrieving it:

do{
            let decodedPlaylists = try NSKeyedUnarchiver.unarchivedObject(ofClasses: [Playlist.self], from: decoded!) as! [Playlist]
            print("here is decoded playlist: \(decodedPlaylists)")
            MusicService.shared.playlists = decodedPlaylists
        }catch let error{
            print("error when retrieve \(error)")
        }

Full error description:

Domain=NSCocoaErrorDomain Code=4864 "value for key 'root' was of unexpected class 'NSArray'. Allowed classes are '{(
    MusicCloud.Playlist
)}'."

Can anyone show me if I'm missing something. Many thanks!

@DávidPásztor can you explain more? I'm new to this kind of local storage, many thanks — hrtlkr29, May 20 '19 at 09:02
See [this](https://stackoverflow.com/questions/52366070/how-to-save-a-dictionary-of-dictionaries-to-userdefaults-intintint/52366193?r=SearchResults&s=3|36.7859#52366193) and [this](https://stackoverflow.com/questions/49925692/save-an-object-in-nsuserdefaults-and-realm/49926513#49926513) answer on how to achieve that. `NSCoding` is the legacy way of saving custom objects to the file system, while `Codable` is a new, pure Swift solution, which is more type safe, so you should be using that instead of the legacy solution. — Dávid Pásztor, May 20 '19 at 09:04

score 8 · Accepted Answer · answered May 20 '19 at 08:58

8

I don't know why but changing from

let decodedPlaylists = try NSKeyedUnarchiver.unarchivedObject(ofClasses: [Playlist.self], from: decoded!) as! [Playlist]

to

let decodedPlaylists = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(decoded!) as! [Playlist]

will fix the issue for me. So I will close my ticket here. Thank you if you're noticing!

answered May 20 '19 at 08:58

hrtlkr29

383
1
7
21

`.unarchiveTopLevelObjectWithData` has been deprecated as of iOS 12.0, and `.unarchivedObject` should be used in its place. – YourManDan Aug 12 '23 at 21:08

score 3 · Answer 2 · answered Apr 12 '20 at 16:23

try this

let decodedPlaylists = try NSKeyedUnarchiver.unarchivedObject(ofClasses: [Playlist.self, NSArray.self], from: decoded!) as! [Playlist]

I guess,

the following decoding code contains the data structure of NSArray

let songs = aDecoder.decodeObject(forKey: "songs") as! [Song]

"Value for key 'root' was unexpected class 'NSArray'" error when retrieve an array of object in UserDefault, Swift

2 Answers2