Saving array of [String: Any] to user default crash occasionally? - swift

Question

I try to save an array of [String: Any] to user default, and for some situations it works, but others do not. I use the following to save to the default:
static func savingQueueToDisk(){
let queueDict = App.delegate?.queue?.map({ (track) -> [String: Any] in
return track.dict
})
if let queueDict = queueDict{
UserDefaults.standard.set(queueDict, forKey: App.UserDefaultKey.queue)
UserDefaults.standard.synchronize()
}
}
Queue is an array of Track, which is defined as follows:
class Track {
var dict: [String: Any]!
init(dict: [String: Any]) {
self.dict = dict
}
var album: Album?{
guard let albumDict = self.dict[AlbumKey] as? [String: Any] else{
return nil
}
return Album(dict: albumDict)
}
var artists: [Artist]?{
guard let artistsDict = self.dict[ArtistsKey] as? [[String: Any]] else{
return nil
}
let artists = artistsDict.map { (artistdict) -> Artist in
return Artist(dict: artistdict)
}
return artists
}
var id: String!{
return self.dict[IdKey] as! String
}
var name: String?{
return self.dict[NameKey] as? String
}
var uri: String?{
return self.dict[URIKey] as? String
}
}
I got different output when retrieving from the same API
Crashing output:
http://www.jsoneditoronline.org/?id=cb45af75a79aff64995e01e5efc0e7b6
Valid output:
http://www.jsoneditoronline.org/?id=0939823a4ac261bd4cb088663c092b20

Answer 1

It turns out it's not safe to just store an array of [String: Any] to the user defaults directly, and it might break based on the data it contains, and hence complaining about can't set none-property-list to user defaults. I solve this by first convert the array of [String: Any] to Data using JSONSerializationand now it can be saved correctly.
Solution:
//saving current queue in the app delegate to disk
static func savingQueueToDisk(){
if let queue = App.delegate?.queue{
let queueDict = queue.map({ (track) -> [String: Any] in
return track.dict
})
if let data = try? JSONSerialization.data(withJSONObject: queueDict, options: []){
UserDefaults.standard.set(data, forKey: App.UserDefaultKey.queue)
UserDefaults.standard.synchronize()
}else{
print("data invalid")
}
}
}
//retriving queue form disk
static func retrivingQueueFromDisk() -> [Track]?{
if let queueData = UserDefaults.standard.value(forKey: App.UserDefaultKey.queue) as? Data{
guard let jsonObject = try? JSONSerialization.jsonObject(with: queueData, options: []) else{
return nil
}
guard let queueDicts = jsonObject as? [[String: Any]] else{
return nil
}
let tracks = queueDicts.map({ (trackDict) -> Track in
return Track(dict: trackDict)
})
return tracks
}
return nil
}