Save NSArray of Class to cacheDirectory

I'd like to NSArray of Class to the cacheDirectory. I've wrote as following, however it returns false. Could you tell me how to solve this problem? Thank you for your kindness.

let paths2 = NSSearchPathForDirectoriesInDomains(
        .CachesDirectory,
        .UserDomainMask, true)
    let cachesPath: AnyObject = paths2[0]

    var cachedQuestions:NSArray = questions as NSArray
    let filePath = cachesPath.stringByAppendingPathComponent("CachedQuestions")

    class Dog {
        var id:Int?
        var name:String?
        init(id:Int, name:String) {
            self.id = id
            self.name = name
        }
    }

    var dogs = [Dog]()
    dogs.append(Dog(id:1, name:"taro"))
    dogs.append(Dog(id:2, name:"jiro"))
    var nsArrayDogs:NSArray = dogs as NSArray

    let success = nsArrayDogs.writeToFile(filePath, atomically: true)

    if success {
        println("save success")
    }

Xcode 11 • Swift 5.1

You can make your Dog class NSCoding compliant:

class Dog: NSObject, NSCoding {
    let id: Int
    let name: String
    required init(id: Int, name: String) {
        self.id = id
        self.name = name
    }
    required init(coder decoder: NSCoder) {
        self.id = decoder.decodeInteger(forKey: "id")
        self.name = decoder.decodeObject(forKey: "name") as? String ?? ""
    }
    func encode(with coder: NSCoder) {
        coder.encode(id, forKey: "id")
        coder.encode(name, forKey: "name")
    }
}

Then you can save your array data to disk as follow:

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        let dog1 = Dog(id: 1, name: "taro")
        let dog2 = Dog(id: 2, name: "jiro")
        do {
            let cachesDirectoryURL = try FileManager.default.url(for: .cachesDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
            let array = [dog1, dog2]
            let fileURL = cachesDirectoryURL.appendingPathComponent("CachedQuestions.plist")
            let data = try NSKeyedArchiver.archivedData(withRootObject: array, requiringSecureCoding: false)
            try data.write(to: fileURL)
            print("saved")  // "saved\n"
            // to load it from disk
            if let dogs = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(Data(contentsOf: fileURL)) as? [Dog] {
                print(dogs.count)   // 2
            }
        } catch {
            print(error)
        }
    }
}