Conforming Class to NSCoding

Question

I conformed my following Person class to NSCoding protocol.

class Person: NSObject, NSCoding{

    var age:Int
    var height: Double
    var name: String

    init(age:Int, height: Double, name:String){
        self.age = age
        self.height = height
        self.name = name
    }

    func encode(with aCoder: NSCoder){
        aCoder.encode(age, forKey: "age")
        aCoder.encode(height, forKey: "height")
        aCoder.encode(name, forKey: "name")
    }

    required init?(coder aDecoder: NSCoder){
        age = aDecoder.decodeObject(forKey: "age") as! Int **//error**
        height = aDecoder.decodeObject(forKey: "height") as! Double
        name = aDecoder.decodeObject(forKey: "name") as! String
        super.init()
    }


}

Then, I created an array of this class. I archived it to a plist using NSKeyedArchiver and everything was fine. However, when I tried to unarchive it I got an error involving unwrapping a optional which was nil. The error showed up in the Person class where marked. This is the code I used:

 if let people = unarchive(){
            print(people)
 }

Here's the function for unarchiving:

func unarchive()->[Person]?{
    let paths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)
    let documentDirectory = paths[0]
    let path = documentDirectory.appending("ObjectData.plist")
    let fileManager = FileManager.default
    if(!fileManager.fileExists(atPath: path)){
        if let bundlePath = Bundle.main.path(forResource: "ObjectData", ofType: "plist"){
            do{
                try fileManager.copyItem(atPath: bundlePath, toPath: path)
            }catch{
                print("problem copying")
            }
        }
    }
    if let objects = NSKeyedUnarchiver.unarchiveObject(withFile: path){
        if let people = objects as? [Person]{
            return people
        }else{
            return nil
        }
    }else{
        return nil
    }
}

Answer 1

Int and Double are not archived as objects. aDecoder.decodeObject(forKey: <key>) for them will always return nil, and using as! with nil will crash your app.

So, instead use this:

aDecoder.decodeInteger(forKey: "age")
aDecoder.decodeDouble(forKey: "height")

For name field you may keep your code.

Answer 2

You should use the proper decoding methods for Int and Double. You could paste the following code in a playground and test it :

import Foundation

class Person: NSObject, NSCoding{

    var age:Int
    var height: Double
    var name: String

    init(age:Int, height: Double, name:String){
        self.age = age
        self.height = height
        self.name = name
    }

    func encode(with aCoder: NSCoder) {
        aCoder.encode(age, forKey: "age")
        aCoder.encode(height, forKey: "height")
        aCoder.encode(name, forKey: "name")
    }

    required init?(coder aDecoder: NSCoder) {
        age = aDecoder.decodeInteger(forKey: "age")
        height = aDecoder.decodeDouble(forKey: "height")
        name = aDecoder.decodeObject(forKey: "name") as! String
        super.init()
    }
}

let john = Person(age: 30, height: 170, name: "John")
let mary = Person(age: 25, height: 140, name: "Mary")

let guys = [john, mary]

let data = NSKeyedArchiver.archivedData(withRootObject: guys)
let people = NSKeyedUnarchiver.unarchiveObject(with: data)

dump (people)