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

问题

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

回答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
    }

来源：https://stackoverflow.com/questions/44010721/saving-array-of-string-any-to-user-default-crash-occasionally

标签

swift

userdefaults