Saving Array of Struct with NSKeyedArchiver and Userdefault in which object conform to NSCoding

Question

As a Protocol oriented programming concept, I have created my model with Struct.

I want to save Array of "Struct" into Userdefault. But I am having a problem in encode/decode of the array of this model.

Here is my model Struct

struct Room {
    let name : String
    let id : String
    let booked : Bool
}

Here I created a extension like this

extension Room {


func decode() -> Room? {
    let userClassObject = NSKeyedUnarchiver.unarchiveObject(withFile: RoomClass.path()) as? RoomClass
    return userClassObject?.room
}

func encode() {
    let personClassObject = RoomClass(room: self)
    NSKeyedArchiver.archiveRootObject(personClassObject, toFile: RoomClass.path())
}

class RoomClass: NSObject, NSCoding {

    var room : Room?

    init(room: Room) {
        self.room = room
        super.init()
    }

    class func path() -> String {
        let documentsPath = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true).first
        let path = documentsPath?.appending(("/Room"))
        return path!
    }

    func encode(with aCoder: NSCoder) {
        aCoder.encode(room!.name, forKey: "name")
        aCoder.encode(room!.id, forKey: "Id")
        aCoder.encode(room!.booked, forKey: "booked")
    }

    required init?(coder aDecoder: NSCoder) {
        let _name = aDecoder.decodeObject(forKey: "name") as? String
        let _id = aDecoder.decodeObject(forKey: "Id") as? String
        let _booked = aDecoder.decodeBool(forKey: "booked")

        room = Room(name: _name!, id: _id!, booked: _booked)

        super.init()
    }
}
}

When I am trying to save arrRoomList(a Array of Room objects) like this

        self.saveRooms(arrayRooms: arrRoomList)

I got this error

[_SwiftValue encodeWithCoder:]: unrecognized selector sent to instance

I have also tried to encode each object first and then try to save them in default, then also it gives an error.

Can anyone please guide me how to encode/decode the array of Struct in Userdefaults in a proper way without converting it into Dictionary?

Answer 1

you can setup the struct to use NSKeyedArchiver directly like this:

struct Room {
    let name : String
    let id : String
    let booked : Bool
}

extension Room {
    func encode() -> Data {
        let data = NSMutableData()
        let archiver = NSKeyedArchiver(forWritingWith: data)
        archiver.encode(name, forKey: "name")
        archiver.encode(id, forKey: "id")
        archiver.encode(booked, forKey: "booked")
        archiver.finishEncoding()
        return data as Data
    }

    init?(data: Data) {
        let unarchiver = NSKeyedUnarchiver(forReadingWith: data)
        defer {
            unarchiver.finishDecoding()
        }
        guard let name = unarchiver.decodeObject(forKey: "name") as? String else { return nil }
        guard let id = unarchiver.decodeObject(forKey: "id") as? String else { return nil }
        booked = unarchiver.decodeBool(forKey: "booked")
        self.name = name
        self.id = id
    }
}

to use with UserDefaults, call like this:

// to encode to data and save to user defaults
let room = Room(name: "asdf", id: "123", booked: true)
UserDefaults.standard.set(room.encode(), forKey: "room")

// to retrieve from user defaults
if let data = UserDefaults.standard.object(forKey: "room") as? Data {
    let room = Room(data: data)
}

Can save/retrieve an array of rooms like this:

func saveRooms(arrayRooms: [Room]) {
    let roomsData = arrayRooms.map { $0.encode() }
    UserDefaults.standard.set(roomsData, forKey: "rooms")
}

func getRooms() -> [Room]? {
    guard let roomsData = UserDefaults.standard.object(forKey: "rooms") as? [Data] else { return nil }
    return roomsData.flatMap { return Room(data: $0) }
}


// save 2 rooms to user defaults
let roomA = Room(name: "A", id: "123", booked: true)
let roomB = Room(name: "B", id: "asdf", booked: false)
saveRooms(arrayRooms: [roomA, roomB])

// get the rooms
print(getRooms())

Answer 2

You can try Model like

class CardModel: NSObject
{
    let name : String
    let id : String
    let booked : Bool

    override init()
    {
        self.name = ""
        self.id = ""
        self.booked = false
    }

    required init(coder aDecoder: NSCoder)
    {
        self.name = aDecoder.decodeObject(forKey: "name") as! String
        self.id = aDecoder.decodeObject(forKey: "id") as! String
        self.booked = aDecoder.decodeObject(forKey: "booked") as! Bool
     }

    func encodeWithCoder(_ aCoder: NSCoder)
    {
        aCoder.encode(name, forKey: "name")
        aCoder.encode(id, forKey: "id")
        aCoder.encode(booked, forKey: "booked")
    }
}

Use by Creating CardModel model Object

let objCardModel = CardModel()
objCardModel.name = "Shrikant"
objCardModel.id = "8"
objCardModel.booked = true

Access by object

let userName = objCardModel.name